1
AAT1231
DATA SHEET
Step-Up DC/DC Converters for White LED Backlight Applications
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202109A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012
General Description
The AAT1231/1231-1 are high frequency, high efficiency
constant current boost converters capable of 24V maxi-
mum output voltage. Both devices are ideal power solu-
tions for backlight applications with up to six white LEDs
in series or up to twelve white LEDs in a parallel/series
configuration. The input voltage is 2.7V to 5.5V for single-
cell lithium-ion/polymer (Li-ion) based portable devices.
The LED current is digitally controlled across a 6x oper-
ating range using Skyworks' Simple Serial Control™
(S2Cwire™) interface. Programmability across 26 dis-
crete current steps provides high resolution, low noise,
flicker-free, constant LED outputs. In programming
AAT1231 operation, LED brightness increases based on
the data received at the EN/SET pin. In programming
AAT1231-1 operation, LED brightness decreases based
on the data received at the EN/SET pin. The SEL logic pin
changes the feedback voltage between two program-
mable ranges.
The AAT1231 and the AAT1231-1 feature high current
limit and fast, stable transitions for stepped or pulsed
current applications. The high switching frequency (up to
2MHz) provides fast response and allows the use of
ultra-small external components, including chip induc-
tors and capacitors. Fully integrated control circuitry
simplifies design and reduces total solution size. The
AAT1231 and the AAT1231-1 offer a true load disconnect
feature which isolates the load from the power source
while in the OFF or disabled state. This eliminates leak-
age current, making the devices ideally suited for bat-
tery-powered applications.
The AAT1231 and the AAT1231-1 are available in Pb-free,
thermally-enhanced 12-pin TSOPJW packages.
Features
• InputVoltageRange:2.7Vto5.5V
• MaximumContinuousOutput24V@50mA
• Drives 6 LEDs in Series, 12 LEDs in Parallel / Series
Configuration
▪ Constant LED Current with 6% Accuracy
• DigitalControlwithS2Cwire Single Wire Interface
▪ 26 Discrete Steps
▪ NoPWMControlRequired
▪ No Additional Circuitry
• Upto82%Efficiency
• Upto2MHzSwitchingFrequencyAllowsSmallExternal
Chip Inductor and Capacitors
• HystereticControl
▪ No External Compensation Components
▪ ExcellentLoadTransientResponse
▪ High Efficiency at Light Loads
• IntegratedSoftStartwithNoExternalCapacitor
• True Load Disconnect Guarantees <1.0µA Shutdown
Current
• SelectableFeedbackVoltageRangesforHighResolution
Control of Load Current
• Short-Circuit,Over-Voltage,andOver-Temperature
Protection
• 12-PinTSOPJWPackage
• -40°Cto+85°CTemperatureRange
Applications
• DigitalStillCameras(DSCs)
• MobileHandsets
• MP3Players
• PDAsandNotebookPCs
• WhiteLEDDrivers
Typical Application
LIN
C2
2.2µF
R2
226kΩ
R3
12kΩ
R1 (RBALLAST)
30.1Ω
C1
2.2µF
L = 2.2µH DS1
Capable of Driving
Six LEDs in Series
(see Applications Section)
OSRAM
LW M678
EN/SET
PGND
PVIN
AAT1231/
1231-1
SW
FB
SEL
Up to 24V/
50mA max
VIN
AGND
OVP
Li-Ion:
VIN = 2.7V to 4.2V
Enable/Set
Select
2
AAT1231
DATA SHEET
Step-Up DC/DC Converters for White LED Backlight Applications
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202109A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012
Pin Descriptions
Pin # Symbol Function
1 PVIN Input power pin; connected to the source of the P-channel MOSFET. Connect to the input
capacitor(s).
2 EN/SET IC enable pin and S2Cwire input control to set output current.
3 SEL
FB voltage range select.
FortheAAT1231,alogicLOWsetstheFBvoltagerangefrom0.1Vto0.4V;alogicHIGHsetsthe
FBvoltagerangefrom0.3Vto0.6V.
FortheAAT1231-1,alogicLOWsetstheFBvoltagerangefrom0.4Vto0.1V;alogicHIGHsetsthe
FBvoltagerangefrom0.6Vto0.3V.
4 VIN Input voltage for the converter. Connect directly to the PVIN pin.
5 N/C No connection.
6, 7 SW Boost converter switching node. Connect the power inductor between this pin and LIN.
8 PGND Power ground for the boost converter.
9AGND Groundpin.
10 FB Feedback pin. Connect a resistor to ground to set the maximum LED current.
11 OVP Feedback pin for over-voltage protection sense.
12 LIN Switched power input. Connect the power inductor between this pin and SW.
Pin Configuration
TSOPJW-12
(Top View)
1
2
3
4
5
6
12
11
10
9
8
7
PVIN
EN/SET
SEL
VIN
N/C
SW
LIN
OVP
FB
AGND
PGND
SW
3
AAT1231
DATA SHEET
Step-Up DC/DC Converters for White LED Backlight Applications
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202109A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012
Part Number Descriptions
Part Number
SEL Polarity
S2Cwire Feedback Voltage ProgrammingHIGH LOW
AAT1231ITP 0.3V≤ VFB ≤0.6V 0.1V≤ VFB ≤0.4V See Table 2
AAT1231ITP-1 0.6V≥ VFB ≥0.3V 0.4V≥ VFB ≥0.1V See Table 3
Absolute Maximum Ratings1
TA=25°Cunlessotherwisenoted.
Symbol Description Value Units
PVIN, VIN Input Voltage -0.3to6.0 V
SW Switching Node 28 V
LIN, EN/SET, SEL, FB MaximumRating VIN+0.3 V
TJOperatingTemperatureRange -40to150 °C
TSStorageTemperatureRange -65to150 °C
TLEAD MaximumSolderingTemperature(atleads,10sec) 300 °C
Thermal Information
Symbol Description Value Units
qJA ThermalResistance 160 °C/W
PDMaximum Power Dissipation 625 mW
1. StressesabovethoselistedinAbsoluteMaximumRatingsmaycausepermanentdamagetothedevice.Functionaloperationatconditionsotherthantheoperatingconditions
specifiedisnotimplied.OnlyoneAbsoluteMaximumRatingshouldbeappliedatanyonetime.
4
AAT1231
DATA SHEET
Step-Up DC/DC Converters for White LED Backlight Applications
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202109A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012
Electrical Characteristics1
TA=-40°Cto+85°Cunlessotherwisenoted.Typicalvaluesareat25°C,VIN = 3.6V.
Symbol Description Conditions Min Typ Max Units
Power Supply
PVIN, VIN InputVoltageRange 2.7 5.5 V
VOUT(MAX) Maximum Output Voltage 24 V
IQOperating Current SEL=GND,FB=0.1V 40 70 µA
ISHDN Shutdown Current EN/SET=GND 1.0 µA
IOUT Maximum Continuous Output Current22.7V<VIN<5.5V,VOUT = 24V 50 mA
DVLINEREG(FB)/
DVIN
LineRegulation VIN = 2.7V to 5.5V, VFB=0.6V 0.7 %/V
RDS(ON) L LowSideSwitchOnResistance 80 mW
TSS Soft-Start Time FromEnabletoOutputRegulation;
VFB=300mV 300 µs
VOVP Over-Voltage Protection Threshold VOUTRising 1.1 1.2 1.3 V
Over-Voltage Hysteresis VOUT Falling 100 mV
ILIMIT N-Channel Current Limit 2.5 A
TSD TJ Thermal Shutdown Threshold 140 °C
THYS TJ Thermal Shutdown Hysteresis 15 °C
SEL, EN/SET
VSEL(L) SEL Threshold Low 0.4 V
VSEL(H) SEL Threshold High 1.4 V
VEN/SET(L) Enable Threshold Low 0.4 V
VEN/SET(H) Enable Threshold High 1.4 V
TEN/SET (LO) EN/SET Low Time VEN/SET<0.6V 0.3 75 µs
TEN/SET(HI) EN/SET High Time VEN/SET > 1.4V 75 µs
TOFF EN/SET Off Timeout VEN/SET<0.6V 500 µs
TLAT EN/SET Latch Timeout VEN/SET > 1.4V 500 µs
IEN/SET EN/SET Input Leakage VEN/SET = 5V, VIN = 5V -1 1 µA
AAT1231
FB FBPinRegulation
VIN=2.7Vto5.5V,SEL=GND,
EN/SET=HIGH 0.09 0.1 0.11
V
VIN=2.7Vto5.5V,SEL=HIGH,
EN/SET = DATA16 0.564 0.6 0.636
AAT1231-1
FB FBPinRegulation
VIN=2.7Vto5.5V,SEL=GND,
EN/SET = DATA16 0.09 0.1 0.11
V
VIN=2.7Vto5.5V,SEL=HIGH,
EN/SET=HIGH 0.564 0.6 0.636
1. Specificationoverthe-40°Cto+85°Coperatingtemperaturerangeisassuredbydesign,characterization,andcorrelationwithstatisticalprocesscontrols.
2. Maximum continuous output current increases with reduced output voltage, but may vary depending on operating efficiency and thermal limitations.
5
AAT1231
DATA SHEET
Step-Up DC/DC Converters for White LED Backlight Applications
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202109A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012
Typical Characteristics
Efficiency vs. LED Current
(4 White LEDs; RBALLAST = 30.1Ω)
LED Current (mA)
Efficiency (%)
77
78
79
80
81
82
83
84
85
246810 12 14 16 18 20
V
IN
= 3.6V V
IN
= 4.2V
V
IN
= 5V
Efficiency vs. LED Current
(5 White LEDs; RBALLAST = 30.1Ω)
LED Current (mA)
Efficiency (%)
75
76
77
78
79
80
81
82
83
246810 12 14 16 18 20
V
IN
= 3.6V
V
IN
= 4.2V
V
IN
= 5V
Efficiency vs. LED Current
(6 White LEDs; RBALLAST = 30.1Ω)
LED Current (mA)
Efficiency (%)
73
74
75
76
77
78
79
80
81
246810 12 14 16 18 20
V
IN
= 3.6V
V
IN
= 4.2V
V
IN
= 5V
Efficiency vs. LED Current
(12 White LEDs; RBALLAST = 30.1Ω)
LED Current (mA)
Efficiency (%)
74
75
76
77
78
79
80
81
82
83
84
246810 12 14 16 18 20
V
IN
= 3.6V
V
IN
= 4.2V
V
IN
= 5V
Shutdown Current vs. Input Voltage
(EN = GND)
Input Voltage (V)
Shutdown Current (µA)
0.0
0.2
0.4
0.6
0.8
1.0
2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
-40°C
85°C
25°C
Feedback Voltage vs. Temperature
(RBALLAST = 30.1Ω)
Temperature (°C)
Feedback Voltage (mV)
0
100
200
300
400
500
600
700
-40 -15 10 35 60 85
6
AAT1231
DATA SHEET
Step-Up DC/DC Converters for White LED Backlight Applications
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202109A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012
Typical Characteristics
Accuracy ILED vs. Temperature
(VFB = 0.6V; RBALLAST = 30.1Ω)
Temperature (°C)
Accuracy ILED (%)
-1.0
-0.8
-0.5
-0.3
0.0
0.3
0.5
0.8
1.0
-40 -15 10 35 60 85
Accuracy ILED vs. Input Voltage
(VFB = 0.6V; RBALLAST = 30.1Ω)
Input Voltage (V)
Accuracy ILED (%)
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
2.7 3.2 3.7 4.2 4.7 5.2 5.7
-40°C
25°C
85°C
Line Transient
(6 White LEDs; RBALLAST = 30.1Ω)
Input Voltage (top) (V)
Output Voltage (middle) (V)
Feedback Voltage (bottom) (V)
Time (50µs/div)
20.2
20.4
20.6
20.8
0.4
0.6
0.8
3.6V
4.2V
Shutdown
(VFB = 0.6V; ILED = 20mA)
Enable Voltage (V) (top)
Feedback Voltage (V) (middle)
Inductor Current (A) (bottom)
Time (50µs/div)
0
0.2
0.4
0.6
0.0
0.5
2.5V
0V
Output Ripple
(6 White LEDs; ILED = 13mA)
Time (400ns/div)
VOUT (DC
Offset 19.8V)
(50mV/div)
VLX (V)
IL (A) 0
0.5
0
20
Output Ripple
(6 White LEDs; ILED = 20mA)
Time (200ns/div)
VOUT (DC
Offset 20.7V)
(20mV/div)
VLX (V)
IL (A) 0
0.5
0
20
7
AAT1231
DATA SHEET
Step-Up DC/DC Converters for White LED Backlight Applications
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202109A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012
Typical Characteristics
AAT1231 Soft Start with S2Cwire
(6 White LEDs; VFB = 0.6V)
Time (100µs/div)
0
0.2
0.4
0
1
2
0V
2.5V
Enable Voltage (top) (V)
Feedback Voltage (middle) (V)
Inductor Current (bottom) (A)
AAT1231 Soft Start
(6 White LEDs; VFB = 0.3V)
Enable Voltage (top) (V)
Feedback Voltage (middle) (V)
Inductor Current (bottom) (A)
Time (50µs/div)
0
0.2
0
1
2
0V
2.5V
AAT1231-1 Soft Start with S2Cwire
(6 White LEDs; VFB = 0.3V)
Enable Voltage (top) (V)
Feedback Voltage (middle) (V)
Inductor Current (bottom) (A)
Time (100µs/div)
0
0.2
0.4
0.6
0
1
0V
2.5V
AAT1231-1 Soft Start
(6 White LEDs; VFB = 0.6V)
Enable Voltage (top) (V)
Feedback Voltage (middle) (V)
Inductor Current (bottom) (A)
Time (50µs/div)
0
0.2
0.4
0.6
0
1
0V
2.5V
Transition of LED Current
(6 White LEDs; SEL = Low; ILED = 13.3mA to 6.6mA)
Output Voltage (top) (V)
Feedback Voltage (bottom) (V)
Time (20µs/div)
18
20
22
0.0
0.1
0.2
0.3
0.4
Transition of LED Current
(6 White LEDs; SEL = Low; I
LED
= 3.3mA to 13.3mA)
Output Voltage (top) (V)
Feedback Voltage (bottom) (V)
Time (20µs/div)
18
20
22
0.0
0.1
0.2
0.3
0.4
8
AAT1231
DATA SHEET
Step-Up DC/DC Converters for White LED Backlight Applications
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202109A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012
Typical Characteristics
EN/SET Latch Timeout vs. Input Voltage
Input Voltage (V)
EN/SET Latch Timeout (µs)
100
150
200
250
300
350
2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
85°C
-40°C
25°C
EN/SET Off Timeout vs. Input Voltage
Input Voltage (V)
EN/SET Off Timeout (µs)
50
100
150
200
250
300
2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
25°C
85°C
-40°C
EN/SET Low Threshold vs. Input Voltage
Input Voltage (V)
VIL (V)
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
-40°C
25°C85°C
EN/SET High Threshold vs. Input Voltage
Input Voltage (V)
VIH (V)
0.6
0.5
0.4
0.7
0.8
0.9
1.0
1.1
1.2
2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
25°C85°C
-40°C
Low Side Switch On Resistance
vs. Input Voltage
Input Voltage (V)
RDS(ON)L (m
Ω
)
40
60
80
100
120
140
160
2.5 3 3.5 4 4.5 5 5.5 6
120°C
100°C
25°C85°C
Input Disconnect Switch Resistance
vs. Input Voltage
Input Voltage (V)
RDS(ON)IN (m
Ω
)
140
160
180
200
220
240
260
280
300
2.5 3 3.5 4 4.5 5 5.5 6
120°C100°C
25°C
85°C
9
AAT1231
DATA SHEET
Step-Up DC/DC Converters for White LED Backlight Applications
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202109A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012
Functional Description
The AAT1231 and the AAT1231-1 consist of a DC/DC
boost controller, an integrated slew rate controlled input
disconnect MOSFET switch, and a high voltage MOSFET
power switch. A high voltage rectifier, power inductor,
output capacitor, and sense resistors are required to
implement a DC/DC constant current boost converter.
The input disconnect switch is activated when a valid
input voltage is present and the EN/SET pin is pulled
high. The slew rate control on the P-channel MOSFET
ensures minimal inrush current as the output voltage is
charged to the input voltage, prior to the switching of
the N-channel power MOSFET. Monotonic turn-on is
guaranteed by the integrated soft-start circuitry. Soft-
start eliminates output voltage overshoot across the full
input voltage range and all loading conditions.
The maximum current through the LED string is set by
the ballast resistor and the feedback voltage of the IC.
The output current may be programmed by adjusting
the level of the feedback reference voltage which is pro-
grammed through the S2Cwire interface. The SEL pin
selects one of two feedback voltage ranges. For the
AAT1231 and with a LOW logic level applied to the SEL
pin,theFBpinvoltagecanbeprogrammedfrom0.1Vto
0.4V.WithalogicHIGH applied to the SELpin,theFB
pin voltage can be programmed from 0.3V to 0.6V. In
the AAT1231-1, the SEL function is inverted in that the
FB pin voltage can be programmed from 0.4V to 0.1V
withalogicLOWappliedtotheSELpinand0.6Vto0.3V
withalogicHIGHappliedtotheSELpin.Regardlessof
which device is chosen, the feedback voltage can be set
to any one of 16 current levels within each FB range,
providing high-resolution control of the LED current,
using the single-wire S2Cwire control.
For torch and flash applications where a short duration,
pulsed load is desired, applying a low-to-high transition
ontheAAT1231’sSELpinproducesa1.5xto3.0xLED
current step. In the AAT1231-1 on the other hand, the
LED current step for a low-to-high transition on the SEL
Functional Block Diagram
Control
Reference
Output
Select
FB
SEL
EN/SET
PVIN LIN
SW
AGND PGND
OVP
VIN
10
AAT1231
DATA SHEET
Step-Up DC/DC Converters for White LED Backlight Applications
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202109A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012
pincanbeprogrammedfrom3.0xto1.5x.Inbothprod-
ucts, the step size is determined by the programmed
voltage at the FB pin where the internal default setting
is3.0xintheAAT1231and1.5xintheAAT1231-1.
Control Loop
The AAT1231/1231-1 provide the benefits of current
mode control with a simple hysteretic output current
loop providing exceptional stability and fast response
with minimal design effort. The device maintains excep-
tional constant current regulation, transient response,
and cycle-by-cycle current limit without additional com-
pensation components.
The AAT1231/1231-1 modulate the power MOSFET
switching current to maintain the programmed FB volt-
age. This allows the FB voltage loop to directly program
the required inductor current in order to maintain the
desired LED current.
The switching cycle initiates when the N-channel MOSFET
is turned ON and current ramps up in the inductor. The
ON interval is terminated when the inductor current
reaches the programmed peak current level. During the
OFF interval, the input current decays until the lower
threshold, or zero inductor current, is reached. The lower
current is equal to the peak current minus a preset hys-
teresis threshold, which determines the inductor ripple
current. The peak current is adjusted by the controller
until the LED output current requirement is met.
The magnitude of the feedback error signal determines
the average input current. Therefore, the AAT1231/1231-1
controller implements a programmed current source
connected to the output capacitor, parallel with the LED
string and ballast resistor. There is no right-half plane
zero, and loop stability is achieved with no additional
compensation components.
An increase in the feedback voltage (VFB) results in an
increased error signal sensed across the ballast resistor
(R1). The controller responds by decreasing the peak
inductor current, resulting in lower average current in
the inductor and LED string(s). Alternatively, when the
VFB is reduced, the controller responds by increasing the
peak inductor current, resulting in higher average cur-
rent in the inductor and LED string(s).
Under light load conditions, the inductor OFF interval
current goes below zero and the boost converter enters
discontinuous mode operation. Further reduction in the
load current results in a corresponding reduction in the
switching frequency. The AAT1231/1231-1 provide pulsed
frequency operation which reduces switching losses and
maintains high efficiency under light load conditions.
Operating frequency varies with changes in the input
voltage, output voltage, and inductor size. Once the
boost converter has reached continuous mode, further
increases in the LED current will not significantly change
theoperatingfrequency.Asmall2.2µH(±20%)inductor
is selected to maintain high frequency switching (up to
2MHz) and high efficiency operation for outputs up to
24V.
Soft Start / Enable
The input disconnect switch is activated when a valid
input voltage is present and the EN/SET pin is pulled
high. The slew rate control on the P-channel MOSFET
ensures minimal inrush current as the output voltage is
charged to the input voltage, prior to switching of the
N-channel power MOSFET. Monotonic turn-on is guaran-
teed by the built-in soft-start circuitry. Soft start elimi-
nates output current overshoot across the full input volt-
age range and all loading conditions.
After the soft start sequence has terminated, the initial
LED current is determined by the internal, default FB
voltage across the external ballast resistor at the FB pin.
Additionally, the AAT1231 and the AAT1231-1 have been
designed to offer the system designer two choices for
the default FB voltage based on the state of the SEL pin.
Changing the LED current from its initial default setting
is easy by using the S2Cwire single wire serial interface;
the FB voltage can be increased (as in the AAT1231; see
Table 2) or decreased (as in the AAT1231-1; see Table 3)
relative to the default FB voltage.
Some applications may require the output to be active
when a valid input voltage is present. In these cases,
add a 10kW resistor between the VIN, VP, and EN/SET
pins to avoid startup issues.
11
AAT1231
DATA SHEET
Step-Up DC/DC Converters for White LED Backlight Applications
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202109A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012
Current Limit and
Over-Temperature Protection
The switching of the N-channel MOSFET terminates when
a current limit of 2.5A (typical) is exceeded. This mini-
mizes power dissipation and component stresses under
overload and short-circuit conditions. Switching resumes
when the current decays below the current limit.
Thermal protection disables the AAT1231/1231-1 when
internal dissipation becomes excessive. Thermal protec-
tion disables both MOSFETs. The junction over-tempera-
turethresholdis140°Cwith15°Coftemperaturehys-
teresis. The output voltage automatically recovers when
the over-temperature fault condition is removed.
Over-Voltage Protection
Over-voltage protection prevents damage to the
AAT1231/1231-1 during open-circuit or high output volt-
age conditions. An over-voltage event is defined as a
condition where the voltage on the OVP pin exceeds the
Over-Voltage Threshold Limit (VOVP = 1.2V typical).
When the voltage on the OVP pin has reached the
threshold limit, the converter stops switching and the
output voltage decays. Switching resumes when the
voltage on the OVP pin drops below the lower hysteresis
limit, maintaining an average output voltage between
the upper and lower OVP thresholds multiplied by the
resistor divider scaling factor.
Under-Voltage Lockout
Internal bias of all circuits is controlled via the VIN input.
Under-voltage lockout (UVLO) guarantees sufficient VIN
bias and proper operation of all internal circuitry prior to
soft start.
Application Information
Over-Voltage Protection
OVP Protection with Open Circuit Failure
The OVP protection circuit consists of a resistor network
tied from the output voltage to the OVP pin (see Figure
1). To protect the device from open circuit failure, the
resistor divider can be selected such that the over-volt-
age threshold occurs prior to the output reaching 24V
(VOUT(MAX)). The value of R3 should be selected from
10kW to 20kW to minimize losses without degrading
noise immunity.
R2 = R3 · - 1
VOUT(MAX)
VOVP
R2
R3
COUT
VOUT
AAT1231/1231-1
OVP
GND
Figure 1: Over-Voltage Protection Circuit.
Over Voltage Protection Pin (top) (V)
Inductor Current (bottom (A)
Output Voltage (middle) (V)
Time (5ms/div)
0
1
222
24
26
1.168V
1.224V
Figure 2: Over-Voltage Protection
Open Circuit Response (No LED).
12
AAT1231
DATA SHEET
Step-Up DC/DC Converters for White LED Backlight Applications
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202109A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012
Assume R3 = 12kW and VOUT(MAX) = 24V. Selecting 1%
resistor for high accuracy, this results in R2 = 226kW
(rounded to the nearest standard value). The minimum
OVPthresholdcanbecalculated:

· + 1

VOUT(OVP_MIN) = VOVP(MIN)
= 21.8V
R2
R3
To avoid OVP detection and subsequent reduction in the
programmed output current (see following section), the
maximum operating voltage should not exceed the
minimum OVP set point.
VOUT(MAX) < VOUT(OVP_MIN)
In some cases, this may disallow configurations with
high LED forward voltage (VFLED) and/or greater than five
series white LEDs. VFLED unit-to-unit tolerance can be as
highas+15%ofnominalforwhiteLEDdevices.
OVP Constant Voltage Operation
Underclosed loopconstantcurrentconditions,the out-
put voltage is determined by the operating current, LED
forward voltage characteristics (VFLED), quantity of series
connected LEDs (N), and the feedback pin voltage
(VFB).
VOUT = VFB + N · VFLED
When the rising OVP threshold is exceeded, switching is
stopped and the output voltage decays. Switching auto-
matically restarts when the output drops below the lower
OVPhysteresisvoltage(100mVtypical)and,asaresult,
the output voltage increases. The cycle repeats, main-
taining an average DC output voltage proportional to the
average of the rising and falling OVP levels (multiplied by
the resistor divider scaling factor). High operating fre-
quency and small output voltage ripple ensure DC cur-
rent and negligible flicker in the LED string(s).
The waveform in Figure 3 shows the output voltage and
LED current at cold temperature with a six series white
LED string and VOVP = 19.4V. As shown, the output volt-
age rises as a result of the increased VFLED which triggers
the OVP constant voltage operation. Self heating of the
LEDs triggers a smooth transition back to constant cur-
rent control.
OVP Constant Voltage Operation
ILED
(10mA/div)
VOUT
(5V/div)
ILED
Cold Temperature Applied Self-Recovery
Time (1s/div)
Figure 3: Over-Voltage Protection
Constant Voltage Operation
(6 White LEDs; ILED = 13mA;
R2 = 182kW; R3 = 12kW).
While OVP is active, the maximum LED current program-
ming error (DILED) is proportional to voltage error across
an individual LED (DVFLED).
(N · V
FLED(MAX)
- V
OUT(OVP_MIN)
- V
FB
)
N
∆V
FLED
=
To minimize the DILED error, the minimum OVP voltage
(VOUT(OVP_MIN)) may be increased, yielding a corresponding
increase in the maximum OVP voltage (VOUT(OVP_MAX)).
Measurements should confirm that the maximum switch-
ing node voltage (VSW(MAX))islessthan28Vunderworst-
case operating conditions.

· + 1
+ VF + VRING

VSW(MAX) = VOVP(MAX)
R3
R2
VF = -Schottky Diode DS1 forward voltage at turn-OFF
VRING = Voltage ring occurring at turn-OFF
LED Selection and Current Setting
The AAT1231/1231-1 are well suited for driving white
LEDs with constant current. Applications include main
and sub-LCD display backlighting, and color LEDs.
The LED current is controlled by the FB voltage and the
ballast resistor. For maximum accuracy, a 1% tolerance
resistor is recommended.
13
AAT1231
DATA SHEET
Step-Up DC/DC Converters for White LED Backlight Applications
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202109A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012
Theballastresistor(RBALLAST) value can be calculated as
follows:
V
FB(MAX)
I
LED(MAX)
R
BALLAST
=
where:
VFB(MAX)=0.4VwhenSEL=Low
VFB(MAX)=0.6VwhenSEL=High
i.e.,foramaximumLEDcurrentof20mA(SEL=High):
V
FB
I
LED(MAX)
0.6
0.020
R
BALLAST
= = = 30Ω ≈ 30.1Ω
Maximum ILED
Current (mA)
RBALLAST (W)
SEL = High SEL = Low
50 12.1 8.06
40 15.0 10.0
35 16.9 11.3
30 20.0 13.3
25 24.3 16.2
20 30.1 20.0
15 40.2 26.7
10 60.4 40.2
5121.0 80.6
Table 1: Maximum LED Current and RBALLAST
Resistor Values (1% Resistor Tolerance).
Typical white LEDs are driven at maximum continuous
currentsof15mAto20mA.Formaximumoutput,two
parallel strings of six series LEDs are used. A total out-
put current of 30mA or 40mA is required (15mA to
20mAineachstring).Themaximumquantityofseries
connected LEDs is determined by the minimum OVP
voltage of the boost converter (VOUT(OVP_MIN)), minus the
maximum feedback voltage (VFB(MAX)) divided by the
maximum LED forward voltage (VFLED(MAX)). VFLED(MAX) can
be estimated from the manufacturers’ datasheet at the
maximum LED operating current.

· + 1

VOUT(OVP_MIN) = VOVP(MIN)
R2
R3
(V
OUT(OVP_MIN)
- V
FB(MAX)
)
V
FLED(MAX)
N =
Figure 4 shows the schematic of using six LEDs in series.
Assume VFLED @ 20mA = 3.5V (typical) from LW M673
(OSRAM)datasheet.

· + 1

VOUT(OVP_MIN) = 1.1V = 21.82V
226kΩ
12k
Ω
21.82V
- 0.6V
3.5V
N =
≈
6.1
Therefore, under typical operating conditions, six LEDs
can be used in series.
14
AAT1231
DATA SHEET
Step-Up DC/DC Converters for White LED Backlight Applications
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202109A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012
LED Brightness Control
The AAT1231 and the AAT1231-1 use S2Cwire program-
ming to control LED brightness and does not require
PWM (pulse width modulation) or additional control cir-
cuitry. This feature greatly reduces the burden on a
microcontroller or system IC to manage LED or display
brightness, allowing the user to “set it and forget it.”
With its high-speed serial interface (1MHz data rate), the
output current of the AAT1231 and the AAT1231-1 can
be changed successively to brighten or dim the LEDs in
smooth transitions (i.e., to fade out) or in abrupt steps,
giving the user complete programmability and real-time
control of LED brightness.
0
5
10
15
20
25
147101
6
LED Current (mA)
S2Cwire Data Register
SEL = HIGH
SEL = LOW
(Default)
Figure 5: Programming AAT1231 LED Current
with RBALLAST = 30.1W.
S2Cwire Data Register
LED Current (mA)
0
5
10
15
20
25
147101
31
6
SEL=LOW
SEL=HIGH
(Default)
Figure 6: Programming AAT1231-1 LED Current
with RBALLAST = 30.1W.
Alternatively, toggling the SEL logic pin from low to high
implements stepped or pulsed LED currents by increasing
theFBpinvoltage.Figures7and8illustratetheSELECT
pin scaling factor, defined as the LED current with
SEL=HIGHdividedbytheLEDcurrentwithSEL=LOW.For
theAAT1231,scalingfactorsfrom1.5xto3.0xarepos-
sible, depending on the S2Cwire data register (default =
3.0x).IntheAAT1231-1,thepossiblescalingfactorsare
3.0xto1.5xwiththeinternaldefaultsettingof1.5x.
VIN = 2.7V to 5.5V
C1
2.2µF C2
2.2µF
2.2µH
L1
226K
R2
12K
R3
R1
30.1Ω
VOUT = 24V/20mA
1
2
3
Enable
JP1 R4 10K
1
2
3
Select
JP2
DS1
N/C
5
VIN
1
SW
6PGND 8
EN
2
SEL
3
SW 7
VP
4GND 9
FB 10
OVP 11
LIN 12
TSOP12JW
U1 AAT1231/1231-1 TSOPJW-12
L1 2.2µH SD3814-2R2
C1 2.2µF 10V 0603
C2 2.2µF 25V 0805
D1-D6 LW M673 White LED
DS1 30V 0.2A BAT42W SOD-123
R1 30.1 0603
R2 226K 0603
R3 12K 0603
R4 10K 0603
U1 AAT1231/1231-1
D4
LED
D3
LED
D2
LED
D1
LED
LED
D5
LED
D6
Figure 4: AAT1231/1231-1 White LED Boost Converter Schematic.
15
AAT1231
DATA SHEET
Step-Up DC/DC Converters for White LED Backlight Applications
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202109A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012
1.0
1.5
2.0
2.5
3.0
3.5
14 7101
31
6
S2Cwire Data Register
Select Pin Scaling Factor
(High to Low)
(Default)
Figure 7: AAT1231 SEL Pin Scaling Factor:
ILED (SEL = High) Divided by ILED (SEL = Low).
S2Cwire Data Register
Select Pin Scaling Factor
(Low to High)
(Default)
1. 0
1. 5
2. 0
2. 5
3. 0
3. 5
14 7101
31
6
Figure 8: AAT1231-1 SEL Pin Scaling Factor:
ILED (SEL = High) Divided by ILED (SEL = Low).
S2Cwire Serial Interface
Skyworks' S2Cwire single wire serial interface is a propri-
etary high-speed single-wire interface available only
from Skyworks. The S2Cwire interface records rising
edges of the EN/SET input and decodes them into 16
individual states. Each state corresponds to a reference
feedback voltage setting on the FB pin, as shown in
Table 2.
S2Cwire Serial Interface Timing
The S2Cwire single wire serial interface data can be
clocked-in at speeds up to 1MHz. After data has been
submitted, EN/SET is held high to latch the data for a
period TLAT. The FB pin voltage is subsequently changed
to the level as defined by the state of the SEL logic pin.
When EN/SET is set low for a time greater than TOFF
, the
AAT1231/1231-1 is disabled. When either the AAT1231
or the AAT1231-1 is disabled, the register is reset to its
default value. In the AAT1231, the default register value
setstheFBpinvoltageto0.6ViftheEN/SETpinissub-
sequently pulled HIGH. In the AAT1231-1, the FB pin
voltageissetto0.3Vunderthesamecondition.
S2Cwire Feedback Voltage Programming
The FB pin voltage is set to the default level at initial
powerup. The AAT1231 and the AAT1231-1 are pro-
grammed through the S2Cwire interface. Table 2 illus-
trates FB pin voltage programming for the AAT1231 and
Table 3 illustrates FB pin voltage programming for the
AAT1231-1. The rising clock edges applied at the EN/SET
pin determine the FB pin voltage. If a logic LOW is
applied at the SEL pin, the default feedback voltage
rangefortheAAT1231is0.1Vto0.4V;foralogicHIGH
condition at the SEL pin, the default feedback voltage
range is 0.3V to 0.6V. Conversely, if a logic LOW is
applied at the SEL pin of the AAT1231-1, the default
feedbackvoltagerangebecomes0.4Vto0.1Vand0.6V
to0.3VforalogicHIGHconditionattheSELpin.
1
EN/SET
2n-1 n ≤ 16
Data Reg
0n
0
T
HI
TLO TLAT TOFF
Figure 9: AAT1231/1231-1 S2Cwire Timing Diagram to Program the Output Voltage.
16
AAT1231
DATA SHEET
Step-Up DC/DC Converters for White LED Backlight Applications
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202109A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012
Rising Clock
Edges/Data
Register
SEL = Low SEL = High
Reference
Voltage (V)
LED Current (mA);
RBALLAST = 30.1W
Reference
Voltage (V)
LED Current (mA);
RBALLAST = 30.1W
10.1(default) 3.32 0.3(default) 9.97
20.12 3.99 0.32 10.63
30.14 4.65 0.34 11.30
40.16 5.32 0.36 11.96
50.18 5.98 0.38 12.62
60.20 6.64 0.40 13.29
70.22 7.31 0.42 13.95
8 0.24 7.97 0.44 14.62
90.26 8.64 0.46 15.28
10 0.28 9.30 0.48 15.95
11 0.30 9.97 0.50 16.61
12 0.32 10.63 0.52 17.28
13 0.34 11.30 0.54 17.94
14 0.36 11.96 0.56 18.60
15 0.38 12.62 0.58 19.27
16 0.40 13.29 0.60 19.93
Table 2: AAT1231 S2Cwire Reference Feedback Voltage Control Settings with RBALLAST = 30.1Ω
(Assume Nominal Values).
Rising Clock
Edges/Data
Register
SEL = Low SEL = High
Reference
Voltage (V)
LED Current (mA);
RBALLAST = 30.1W
Reference
Voltage (V)
LED Current (mA);
RBALLAST = 30.1W
10.4(default) 13.29 0.6(default) 19.93
20.38 12.62 0.58 19.27
30.36 11.96 0.56 18.60
40.34 11.30 0.54 17.94
50.32 10.63 0.52 17.28
60.30 9.97 0.50 16.61
70.28 9.30 0.48 15.95
8 0.26 8.64 0.46 15.28
90.24 7.97 0.44 14.62
10 0.22 7.31 0.42 13.95
11 0.20 6.64 0.40 13.29
12 0.18 5.98 0.38 12.62
13 0.16 5.32 0.36 11.96
14 0.14 4.65 0.34 11.30
15 0.12 3.99 0.32 10.63
16 0.10 3.32 0.30 9.97
Table 3: AAT1231-1 S2Cwire Reference Feedback Voltage Control Settings With RBALLAST = 30.1Ω
(Assumes Nominal Values).
17
AAT1231
DATA SHEET
Step-Up DC/DC Converters for White LED Backlight Applications
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202109A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012
Selecting the Schottky Diode
To ensure minimum forward voltage drop and no recov-
ery, high voltage Schottky diodes are considered the
best choice for the AAT1231/1231-1 boost converters.
The output diode is sized to maintain acceptable effi-
ciency and reasonable operating junction temperature
under full load operating conditions. Forward voltage
(VF) and package thermal resistance (qJA) are the domi-
nant factors to consider in selecting a diode. The diode
non-repetitive peak forward surge current rating (IFSM)
should be considered for high pulsed load applications,
such as camera flash. IFSM rating drops with increasing
conduction period. Manufacturers’ datasheets should be
consulted to verify reliability under peak loading condi-
tions. The diode’s published current rating may not
reflect actual operating conditions and should be used
only as a comparative measure between similarly rated
devices.
20VratedSchottkydiodesarerecommendedforoutputs
lessthan15V,while30VratedSchottkydiodesarerec-
ommended for outputs greater than 15V.
The switching period is divided between ON and OFF
time intervals.
= TON + TOFF
1
FS
During the ON time, the N-channel power MOSFET is
conducting and storing energy in the boost inductor.
During the OFF time, the N-channel power MOSFET is
not conducting. Stored energy is transferred from the
input battery and boost inductor to the output load
through the output diode.
Duty cycle is defined as the ON time divided by the total
switching interval.
T
ON
T
ON
+ T
OFF
D =
= T
ON
⋅ F
S
The maximum duty cycle can be estimated from the
relationship for a continuous mode boost converter.
Maximum duty cycle (DMAX) is the duty cycle at minimum
input voltage (VIN(MIN)).
V
OUT
- V
IN(MIN)
V
OUT
D
MAX
=
The average diode current during the OFF time can be
estimated.
I
OUT
1 - D
MAX
I
AVG(OFF)
=
The following curves show the VF characteristics for dif-
ferent Schottky diodes (100°C case). The VF of the
Schottky diode can be estimated from the average cur-
rent during the off time.
Forward Voltage (V)
Forward Current (mA)
10
100
1000
10000
0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70
B340LA
MBR0530T
ZHCS350
BAT42W
The average diode current is equal to the output cur-
rent.
IAVG(TOT) = IOUT
The average output current multiplied by the forward
diode voltage determines the loss of the output diode.
PLOSS(DIODE) = IAVG(TOT) · VF
= IOUT · VF
For continuous LED currents, the diode junction tem-
perature can be estimated.
TJ(DIODE) = TAMB + θJA · PLOSS(DIODE)
18
AAT1231
DATA SHEET
Step-Up DC/DC Converters for White LED Backlight Applications
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202109A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012
Output diode junction temperature should be maintained
below 110ºC, but may vary depending on application
and/or system guidelines. The diode qJA can be mini-
mized with additional PCB area on the cathode. PCB
heat-sinking the anode may degrade EMI performance.
The reverse leakage current of the rectifier must be con-
sidered to maintain low quiescent (input) current and
high efficiency under light load. The rectifier reverse cur-
rent increases dramatically at elevated temperatures.
Selecting the Boost Inductor
The AAT1231 and the AAT1231-1 controllers utilize hys-
teretic control and the switching frequency varies with
output load and input voltage. The value of the inductor
determines the maximum switching frequency of the
boost converter. Increased output inductance decreases
the switching frequency, resulting in higher peak cur-
rents and increased output voltage ripple. To maintain
2MHz maximum switching frequency and stable opera-
tion, an output inductor sized from 1.5µH to 2.7µH is
recommended.
A better estimate of DMAX is possible once VF is known.
(V
OUT
+ V
F
- V
IN(MIN)
)
(V
OUT
+ V
F
)
D
MAX
=
Where VF is the Schottky diode forward voltage. If not
known,itcanbeestimatedat0.5V.
Manufacturer’s specifications list both the inductor DC
current rating, which is a thermal limitation, and peak
inductor current rating, which is determined by the satu-
ration characteristics. Measurements at full load and
high ambient temperature should be completed to
ensure that the inductor does not saturate or exhibit
excessive temperature rise.
The output inductor (L) is selected to avoid saturation at
minimum input voltage, maximum output load condi-
tions. Peak current may be estimated using the follow-
ing equation, assuming continuous conduction mode.
Worst-case peak current occurs at minimum input volt-
age (maximum duty cycle) and maximum load. Switching
frequency (FS) can be estimated from the curves and
assumesa2.2µHinductor.
Output Current (mA)
Switching Frequency (MHz)
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
40 50 60 70 80 90 100
VIN = 2.7V
VOUT = 15V
VIN = 2.7V
VOUT = 18V
VIN = 3.0V
VOUT = 15V
VIN = 3.0V
VOUT = 18V
VIN = 3.6V
VOUT = 15V
VIN = 3.6V
VOUT = 18V
Output Current (mA)
Switching Frequency (MHz)
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
40 50 60 70 80 90 100
VIN = 3.6V
VOUT = 10V
VIN = 3.6V
VOUT = 12V
VIN = 2.7V
VOUT = 12V
VIN = 2.7V
VOUT = 10V
VIN = 3.0V
VOUT = 10V
VIN = 3.0V
VOUT = 12V
I
OUT
(1 - D
MAX
)
D
MAX
·
V
IN(MIN)
(2
·
F
S
·
L)
I
PEAK
= +
Manufacturer Part Number
Rated
Forward
Current (A)
Non-Repetitive
Peak Surge
Current (A)
Rated
Voltage (V)
Thermal
Resistance
(qJA, °C/W) Case
Diodes, Inc. B340LA 370.0 40 25 SMA
Diodes, Inc. BAT42W 0.2 4.0 30 500 SOD-123
ON Semi MBR0530T 0.5 5.5 30 206 SOD-123
Zetex ZHCS350 0.35 4.2 40 330 SOD-523
Central Semi CMDSH2-3 0.2 1.0 30 500 SOD-323
Table 4: Typical Surface Mount Schottky Rectifiers for Various Output Levels.
19
AAT1231
DATA SHEET
Step-Up DC/DC Converters for White LED Backlight Applications
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202109A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012
At light load and low output voltage, the controller
reduces the operating frequency to maintain maximum
operating efficiency. As a result, further reduction in
output load does not reduce the peak current. Minimum
peakcurrentcanbeestimatedfrom0.5Ato0.75A.
At high load and high output voltages, the switching fre-
quency is somewhat diminished, resulting in higher IPEAK.
Bench measurements are recommended to confirm actu-
al IPEAK and ensure that the inductor does not saturate at
maximum LED current and minimum input voltage.
The RMS current flowing through the boost inductor is
equal to the DC plus AC ripple components. Under
worst-case RMS conditions, the current waveform is
criticallycontinuous.TheresultingRMScalculationyields
worst-caseinductorloss.TheRMScurrentvalueshould
be compared against the manufacturer’s temperature
rise, or thermal derating, guidelines.
I
PEAK
I
RMS
=
3
For a given inductor type, smaller inductor size leads to
an increase in DCR winding resistance and, in most
cases, increased thermal impedance. Winding resistance
degrades boost converter efficiency and increases the
inductor’s operating temperature.
PLOSS(INDUCTOR) = IRMS2 · DCR
To ensure high reliability, the inductor case temperature
shouldnotexceed100ºC.Insomecases,PCBheatsink-
ing applied to the LIN node (non-switching) can improve
the inductor’s thermal capability. PCB heatsinking may
degrade EMI performance when applied to the SW node
(switching) of the AAT1231/1231-1.
Shielded inductors provide decreased EMI and may be
requiredinnoisesensitiveapplications.Unshieldedchip
inductors provide significant space savings at a reduced
cost compared to shielded (wound and gapped) induc-
tors. In general, chip-type inductors have increased
winding resistance (DCR) when compared to shielded,
wound varieties.
Inductor Efficiency Considerations
The efficiency for different inductors is shown in Figure
7 for six white LEDs in series. Smaller inductors yield
increasedDCRandreducedoperatingefficiency.
65
68
71
74
77
80
25811141
72
0
LED Current (mA)
Efficiency (%)
Cooper SD3814-2R2 (77mΩ)Cooper SD3110-2R2 (161mΩ)
Figure 10: AAT1231/1231-1 Efficiency for
Different Inductor Types (VIN = 3.6V;
Six White LEDs in Series).
Manufacturer Part Number
Inductance
(µH)
Maximum DC ISAT
Current (mA)
DCR
(mW)
Size (mm)
LxWxH Type
Sumida
www.sumida.com CDRH2D11-2R2 2.2 780 78 3.2x3.2x1.2 Shielded
Cooper Electronics
www.cooperet.com
SD3814-2R2 2.2 1900 77 4.0x4.0x1.4 Shielded
SD3110-2R2 2.2 910 161 3.1x3.1x1.0 Shielded
Murata
www.murata.com
LQH3NPN2R2NG0 2.2 1250 164 3.0x3.0x1.0 Chip Coil Shield
LQM2HPN2R2MG0 2.2 1300 80 2.5x2.0x1.0 Chip Coil Shield
Taiyo Yuden
www.t-yuden.com
NR3010T-2R2M 2.2 1100 95 3.0x3.0x1.0 Shielded
CBC2016T2R2M 2.2 750 200 2.0x1.6x1.6 Chip
Non-Shielded
CBC2518T2R2M 2.2 510 90 2.5x1.8x1.8 Shielded
Table 5: Recommended Inductors for Various Output Levels (Select IPEAK < ISAT).
20
AAT1231
DATA SHEET
Step-Up DC/DC Converters for White LED Backlight Applications
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202109A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012
Selecting the Boost Capacitors
The high output ripple inherent in the boost converter
necessitates low impedance output filtering.
Multi-layer ceramic (MLC) capacitors provide small size
and adequate capacitance, low parasitic equivalent
seriesresistance(ESR)andequivalentseriesinductance
(ESL), and are well suited for use with the AAT1231/1231-1
boostregulator.MLCcapacitorsoftypeX7RorX5Rare
recommended to ensure good capacitance stability over
the full operating temperature range.
The output capacitor is sized to maintain the output load
without significant voltage droop (DVOUT) during the
power switch ON interval, when the output diode is not
conducting. A ceramic output capacitor from 2.2µF to
4.7µF is recommended (see Table 5). Typically, 25V
rated capacitors are required for the 24V maximum
boostoutput.Ceramiccapacitorssizedassmallas0805
are available which meet these requirements.
MLC capacitors exhibit significant capacitance reduction
with applied voltage. Output ripple measurements should
confirm that output voltage droop and operating stability
are acceptable. Voltage derating can minimize this fac-
tor, but results may vary with package size and among
specific manufacturers.
Output capacitor size can be estimated at a switching
frequency (FS)of500kHz(worstcase).
I
OUT
· D
MAX
F
S
· ∆V
OUT
C
OUT
=
To maintain stable operation at full load, the output
capacitor should be sized to maintain DVOUT between
100mVand200mV.
The boost converter input current flows during both ON
and OFF switching intervals. The input ripple current is
less than the output ripple and, as a result, less input
capacitance is required.
PCB Layout Guidelines
Boost converter performance can be adversely affected
by poor layout. Possible impact includes high input and
output voltage ripple, poor EMI performance, and
reduced operating efficiency. Every attempt should be
made to optimize the layout in order to minimize para-
sitic PCB effects (stray resistance, capacitance, and
inductance) and EMI coupling from the high frequency
SW node. A suggested PCB layout for the AAT1231/1231-1
boostconverterisshowninFigures10and11.Thefol-
lowingPCBlayoutguidelinesshouldbeconsidered:
1. Minimize the distance from Capacitor C1 and C2
negative terminal to the PGND pins. This is espe-
cially true with output capacitor C2, which conducts
high ripple current from the output diode back to the
PGNDpins.
2. Minimize the distance between L1 to DS1 and switch-
ing pin SW; minimize the size of the PCB area con-
nected to the SW pin.
3. MaintainagroundplaneandconnecttotheICPGND
pin(s)aswellastheGNDterminalsofC1andC2.
4. Consider additional PCB area on DS1 cathode to
maximize heatsinking capability. This may be neces-
sary when using a diode with a high VF and/or ther-
mal resistance.
5. To avoid problems at startup, add a 10kW resistor
betweentheVIN,VPandEN/SETpins(R4).Thisis
critical in applications requiring immunity from input
noise during “hot plug” events, e.g. when plugged
intoanactiveUSBport.
21
AAT1231
DATA SHEET
Step-Up DC/DC Converters for White LED Backlight Applications
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202109A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012
Manufacturer Part Number Value (µF) Voltage Rating Temp Co Case Size
Murata GRM188R60J225KE19 2.2 6.3 X5R 0603
Murata GRM188R61A225KE34 2.2 10 X5R 0603
Murata GRM219R61E225KA12 2.2 25 X5R 0805
Murata GRM21BR71E225KA73L 2.2 25 X7R 0805
Murata GRM21BR61E475KA12 4.7 25 X5R 0805
Table 6: Recommended Ceramic Capacitors.
Figure 11: AAT1231/1231-1 Evaluation Figure 12: AAT1231/1231-1 Evaluation
Board Top Side Layout (with six LEDs Board Bottom Side Layout (with six LEDs
and microcontroller). and microcontroller).
22
AAT1231
DATA SHEET
Step-Up DC/DC Converters for White LED Backlight Applications
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202109A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012
C1
2.2µF
2.2µH
L1
R2
226K
R3
12K
30.1
R1
VOUT
C2
2.2µF
Schottky
DS1
N/C
5
VIN
1
SW
6PGND 8
EN
2
SEL
3
SW 7
VP
4GND 9
FB 10
OVP 11
LIN 12
AAT1231/1231-1
U1 D1
LED
D2
LED
D3
LED
D4
LED
LED
D5
LED
D6
VDD
1
GP5
2
GP4
3
GP3
4GP2 5
GP1 6
GP0 7
VSS 8
PIC12F675
U2
C3
1µF
R5
1K
VCC
10K
R4
R6
1K
R7
1K
Up
Down
Select
R8
330
D7
RED
12 34 5
0SW1
12 34 5
0SW2
12 34 5
0SW3
D8
GREEN
(Select indicator)
S2Cwire
Microcontroller
AAT1231/1231-1
White LED
Driver
R9
330
1 2 3
J1
JP1
DC- DC+
VCC
J2 J3
U1 Skyworks AAT1231/1231-1 TSOPJW-12 package
U2 PIC12F675
C1 GRM188R60J225KE01
C2 GRM21BR71E225KA73
C3 GRM216R61A105KA01
R1 30.1W, 1%, 1/4W; 0603
R2 226kW, 1%, 1/4W; 0603
R3 12.1kW, 1%, 1/4W; 0603
R4 10kW, 5%, 1/4W; 0603
R5, R6, R7 1KW, 5%, 1/4W; 0805
R8, R9 330W, 5%, 1/4W; 0805
JP1 0W, 5%; 0805
DS1 BAT42W
L1 Cooper Electronics 2.2µH SD3814-2R2
D1-D6 White Hyper-Bright LED LW M673
D7 Red LED 1206
D8 Green LEC 1206
SW1 - SW3 SPST, 5mm
J1, J2, J3 Conn. Header, 2mm
Figure 13: AAT1231/1231-1 Evaluation Board Schematic (with six LEDs and microcontroller).
23
AAT1231
DATA SHEET
Step-Up DC/DC Converters for White LED Backlight Applications
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202109A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012
Additional Applications
LIN
L = 2.2µH DS1
C
2
2.2µF
C
1
2.2µF
R
2
187kΩ
R
3
12kΩ
30.1Ω 20mA
ENSET
PGND
PVIN
AAT1231/
1231-1
SW
FB
SEL
Up to 24V/
50mA max
VIN
AGND
OVP
Li-Ion
V
IN
= 2.7V
to 5.5V
Efficiency vs. LED Current
(4 White LEDs; RBALLAST = 30.1Ω)
LED Current (mA)
Efficiency (%)
77
78
79
80
81
82
83
84
85
246810 12 14 16 18 20
V
IN
= 3.6V V
IN
= 4.2V
V
IN
= 5V
Figure 14: Four LEDs In Series Configuration.
LIN
L = 2.2µH DS1
C
2
2.2µF
C
1
2.2µF
R
2
196kΩ
R
3
12kΩ
30.1Ω 20mA
ENSET
PGND
PVIN
AAT1231/
1231-1
SW
FB
SEL
Up to 24V/
50mA max
VIN
AGND
OVP
Li-Ion
V
IN
= 2.7V
to 5.5V
Efficiency vs. LED Current
(5 White LEDs; RBALLAST = 30.1Ω)
LED Current (mA)
Efficiency (%)
75
76
77
78
79
80
81
82
83
246810 12 14 16 18 20
V
IN
= 3.6V
V
IN
= 4.2V
V
IN
= 5V
Figure 15: Five LEDs In Series Configuration.
24
AAT1231
DATA SHEET
Step-Up DC/DC Converters for White LED Backlight Applications
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202109A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012
LIN
EN/SET
PGND
PVIN
C
2
2.2µF
C
1
2.2µF
R
2
226k
Ω
R
3
12k
Ω
30.1
Ω
20mA
L = 2.2µH DS1
AAT1231/
1231-1
SW
FB
SEL
Up to 24V/
50mA max
VIN
AGND
OVP
Li-Ion
V
IN
= 2.7V
to 5.5V
Efficiency vs. LED Current
(6 White LEDs; RBALLAST = 30.1Ω)
LED Current (mA)
Efficiency (%)
73
74
75
76
77
78
79
80
81
246810 12 14 16 18 20
V
IN
= 3.6V
V
IN
= 4.2V
V
IN
= 5V
Figure 16: Six LEDs In Series Configuration.
LIN
EN/SET
PGND
PVIN
C
2
2.2µF
C
1
2.2µF
R
2
226k
Ω
R
3
12k
Ω
30.1
Ω
20mA
30.1
Ω
20mA
L = 2.2µH DS1
AAT1231/
1231-1
SW
FB
SEL
Up to 24V/
50mA max
VIN
AGND
OVP
Li-Ion
V
IN
= 2.7V
to 5.5V
Efficiency vs. LED Current
(12 White LEDs; RBALLAST = 30.1Ω)
LED Current (mA)
Efficiency (%)
74
75
76
77
78
79
80
81
82
83
84
246810 12 14 16 18 20
V
IN
= 3.6V
V
IN
= 4.2V
V
IN
= 5V
Figure 17: Twelve LEDs In Series/Parallel Configuration.
25
AAT1231
DATA SHEET
Step-Up DC/DC Converters for White LED Backlight Applications
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202109A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012
Multi-String White LED Configurations
for Digital Photo Frame Applications
The AAT1231 and AAT1231-1 can be configured to light
up as many as thirty-two white LEDs (WLED). This solu-
tion is scalable, flexible and good for digital photo frame
applications with multi-strings of WLEDs.
The multi-string WLED configuration can be composed of
many different parallel/series combinations, such as
6S2P, 6S3P, 5S4P, 5S5P, 5S6P, 4S7P, 4S8P, 3S9P, and
3S10P.‘S’isdefinedasthenumberofWLEDsinaseries
per string. ‘P’ is defined as the number of strings of
WLEDs that are connected from the output voltage (VOUT)
to the ballast resistor, or in parallel. To match the
“brightness” of each separate string of WLEDs, each
string must have the same number of WLEDs in them.
The over-voltage protection (OVP) should also be adjust-
ed according to the maximum feedback voltage plus the
maximum forward voltage (VF) of each WLED multiplied
by the total number of WLEDs in any of the parallel
strings of WLEDs. The efficiency of one configuration
(3S7P:3inseriesperstringwith7stringsinparallel)is
showninFigure18.AscalableschematicandPCBlayout
are illustrated in Figures 19 through 21.
Efficiency vs. Total LED Current
(21 White LEDs [3 in Series, 7 in Parallel]; RBALLAST = 4.32Ω)
Total LED Current (mA)
Efficiency (%)
65
70
75
80
85
90
20 40 60 80 100140 160
VIN = 5V
VIN = 4.2V
VIN = 3.6V
Figure 18: Efficiency of the 3S7P
Multi-String Configuration.
Figure 19: Multi-String WLED Application Schematic.
R1
DS1
D Schottky
C1 10V 0603 X5R 2.2µF GRM188R60J225KE01
C2 25V 0805 X7R 2.2µF GRM21BR71E225KA73
DS1 B340LA
L1 2.2µH SD10-2R2, SD12-2R2, SD18-2R2
D1a-D10c White LED
N/C
5
VIN
1
SW
6PGND 8
EN
2
SEL
3
SW 7
VP
4GND 9
FB 10
OVP 11
LIN 12
AAT1231 TSOPJW-12
U1
VDD
1
GP5
2
GP4
3
GP3
4GP2 5
GP1 6
GP0 7
VSS 8
PIC12F675
U2
C3
1µF
C1
2.2µF
L1
2.2µH
C2
2.2µF
VCC
VOUT
VCC
Up
Down
Select
R8
1k R6
1k
R5
1k
R4
1k
R9
10k
R7
1k
R2
220K
R3
12.1K
D12
RED
D11
GREEN
(Select
indicator)
123
J1
JP1
DC- DC+ J2 J3
JP2
D10a
LED
D10b
LED
D10c
LED
D9a
LED
D9b
LED
D9c
LED
D8b
LED
D8a
LED
D8c
LED
D8d
LED
D7b
LED
D7a
LED
D7c
LED
D7d
LED
D6c
LED
D6b
LED
D6a
LED
D6d
LED
D6e
LED
D5c
LED
D5b
LED
D5a
LED
D5d
LED
D5e
LED
D4c
LED
D4b
LED
D4a
LED
D4d
LED
D4e
LED
D3d
LED
D3c
LED
D3b
LED
D3a
LED
D3e
LED
D3f
LED
D2d
LED
D2c
LED
D2b
LED
D2a
LED
D2e
LED
D2f
LED
D1d
LED
D1c
LED
D1b
LED
D1a
LED
D1e
LED
D1f
LED
SW1
SW2
SW3
26
AAT1231
DATA SHEET
Step-Up DC/DC Converters for White LED Backlight Applications
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202109A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012
The ballast resistor R1 is calculated based on the total
number of WLED strings and the total WLED current
required from the AAT1231 or AAT1231-1. The value
of the ballast resistor for each application is listed in
Table 7.
Number of
Parallel Strings
Total LED
Current (A)
R1 (Ω)
1% Tolerance
10 0.20 3.01
90.18 3.32
8 0.16 3.74
70.14 4.32
60.12 4.99
50.10 6.04
40.08 7.50
30.06 10.0
20.04 15.0
10.02 30.1
Table 7: Ballast Resistor Values for
Multi-String WLED Applications.
Figure 20: Top Layer of the Figure 21: Bottom Layer of the
Multi-String WLED Application. Multi-String WLED Application.
27
AAT1231
DATA SHEET
Step-Up DC/DC Converters for White LED Backlight Applications
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202109A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012
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Ordering Information
Package LED Current Control Marking1Part Number (Tape and Reel)2
TSOPJW-12 Increasing SDXYY AAT1231ITP-T1
TSOPJW-12 Decreasing TUXYY AAT1231ITP-1-T1
Skyworks Green™ products are compliant with
all applicable legislation and are halogen-free.
For additional information, refer to Skyworks
Definition of Green™, document number
SQ04-0074.
Package Information
TSOPJW-12
0.20 + 0.10
- 0.05
0.055 ± 0.045 0.45 ± 0.15
7° NOM
4° ± 4°
3.00 ± 0.10
2.40 ± 0.10
2.85 ± 0.20
0.50 BSC 0.50 BSC 0.50 BSC 0.50 BSC 0.50 BSC
0.15 ± 0.05
0.9625
±
0.0375
1.00 + 0.10
- 0.065
0.04 REF
0.010
2.75 ± 0.25
All dimensions in millimeters.
1. XYY=assemblyanddatecode.
2. Sample stock is generally held on part numbers listed in BOLD.