Description
The A6213 is a single IC switching regulator that provides
constant-current output to drive high-power LEDs. It integrates
a high-side N-channel DMOS switch for DC-to-DC step- down
(buck) conversion. A true average current is output using a
cycle-by-cycle, controlled on-time method.
Output current is user-selectable by an external current sense
resistor. Output voltage is automatically adjusted to drive
various numbers of LEDs in a single string. This ensures the
optimal system efficiency.
LED dimming is accomplished by a direct logic input pulse-
width modulation (PWM) signal at the enable pin.
The device is provided in a compact 8-pin narrow SOIC package
(suffix LJ) with exposed pad for enhanced thermal dissipation.
It is lead (Pb) free, with 100% matte-tin leadframe plating.
A62131-DS, Rev. 6
Features and Benefits
• AEC-Q100 qualified
• Supply voltage 6 to 48 V
• True average output current control
• 3 A maximum output over operating temperature range
(1.5 A for A6213-1)
• Cycle-by-cycle current limit
• Integrated MOSFET switch
• Dimming via direct logic input or power supply voltage
• Internal control loop compensation
• Undervoltage lockout (UVLO) and thermal shutdown
protection
• Low power shutdown (1 µA typical)
• Robust protection against:
▫Adjacentpin-to-pinshort
▫Pin-to-GNDshort
▫Componentopen/shortfaults
Automotive-Grade, Constant-Current
PWM Dimmable Buck Regulator LED Driver
Package 8-pin SOICN with exposed
thermal pad (suffix LJ):
Not to scale
A6213 and A6213-1
Typical Application Circuit
C1
R1
GND
VIN
VIN (6 to 48 V)
1
2
3
4
8
7
6
5
SW
GND
VCC
A6213
BOOT
TON
EN
CS
C5
C4 D1
L1 LED+
LED–
RSENSE
EN
Enable/PWM Dimming
(100 Hz to 2 kHz)
. . .
PAD
Applications:
Automotive lighting
• Daytime running lights
• Front and rear fog lights
•Turn/stoplights
• Map light
• Dimmable interior lights
January 21, 2013
Automotive-Grade, Constant-Current
PWM Dimmable Buck Regulator LED Driver
A6213 and
A6213-1
2
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Absolute Maximum Ratings
Characteristic Symbol Notes Rating Unit
Supply Voltage VIN –0.3 to 50 V
Bootstrap Drive Voltage VBOOT –0.3 to VIN + 8 V
Switching Voltage VSW –1.5 to VIN + 0.3 V
Linear Regulator Terminal VCC VCC to GND –0.3 to 7 V
Enable and TON Voltage VEN , VTON –0.3 to VIN + 0.3 V
Current Sense Voltage VCS –0.3 to 7 V
Operating Ambient Temperature TAK temperature range for automotive –40 to 125 °C
Maximum Junction Temperature TJ(max) 150 °C
Storage Temperature Tstg –55 to 150 °C
Selection Guide
Part Number Operating Ambient
Temperature, TA
Package Packing
A6213KLJTR-T –40°C to 125°C 8-pin SOICN with exposed thermal pad 3000 pieces per 13-in reel
A6213KLJTR-1-T –40°C to 125°C 8-pin SOICN with exposed thermal pad 3000 pieces per 13-in reel
Pinout Diagram
SW
BOOT
GND
VCC
VIN
TON
EN
CS
1
2
3
4
8
7
6
5
PAD
Terminal List Table
Number Name Function
1 VIN Supply voltage input terminals
2TON Regulator on-time setting resistor terminal
3 EN Logic input for Enable and PWM dimming
4 CS Drive output current sense feedback
5 VCC Internal linear regulator output
6 GND Ground terminal
7 BOOT DMOS gate driver bootstrap terminal
8 SW Switched output terminals
–PAD Exposed pad for enhanced thermal dissipation;
connect to GND
Thermal Characteristics*: may require derating at maximum conditions; see application section for optimization
Characteristic Symbol Test Conditions* Value Unit
Package Thermal Resistance
(Junction to Ambient) RθJA
On 4-layer PCB based on JEDEC standard 35 °C/W
On 2-layer generic test PCB with 0.8 in.2 of copper area each side 62 °C/W
Package Thermal Resistance
(Junction to Pad) RθJP 2 °C/W
*Additional thermal information available on the Allegro™ website.
Automotive-Grade, Constant-Current
PWM Dimmable Buck Regulator LED Driver
A6213 and
A6213-1
3
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Functional Block Diagram
+
–
+
–
0.2 V
BOOT
CVCC CBOOT L1
D1
LED String
VCC
Shutdown
VIN
V
IN
C
COMP
EN
TON
R
ON
CS
GND
RSENSE
SW
On-Time
Current
Generator
On-Time
Timer
IC and Driver
Control Logic
Level Shift
Gate Drive
UVLO
V
CC
UVLO
Off-Time
Timer
V
REG
5.3 V
+
–
Buck Switch
Current Sense
Current Limit
Off-Time
Timer I
LIM
Thermal
Shutdown
V
CC
UVLO
PAD
Average
+
–
V
IL
= 0.4 V
V
IH
= 1.8 V
Automotive-Grade, Constant-Current
PWM Dimmable Buck Regulator LED Driver
A6213 and
A6213-1
4
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
ELECTRICAL CHARACTERISTICS: Valid at VIN = 24 V, TA = –40°C to 125°C, typical values at TA = 25°C, unless otherwise noted
Characteristics Symbol Test Conditions Min. Typ. Max. Unit
Input Supply Voltage VIN 6 – 48 V
VIN Undervoltage Lockout Threshold VUVLO VIN increasing – 5.3 – V
VIN Undervoltage Lockout Hysteresis VUVLO
_
HYS VIN decreasing – 150 – mV
VIN Pin Supply Current IIN VCS = 0.5 V, EN = high – 5 – mA
VIN Pin Shutdown Current IINSD EN shorted to GND – 1 10 µA
Buck Switch Current Limit Threshold ISWLIM
A6213 3.0 4.0 5.0 A
A6213-1 1.9 2.2 2.5 A
Buck Switch On-Resistance RDS(on) VBOOT = VIN + 4.3 V, TA = 25°C, ISW = 1 A – 0.25 0.4 Ω
BOOT Undervoltage Lockout
Threshold VBOOTUV VBOOT to VSW increasing 1.7 2.9 4.3 V
BOOT Undervoltage Lockout
Hysteresis VBOTUVHYS VBOOT to VSW decreasing – 370 – mV
Switching Minimum Off-Time tOFFmin VCS = 0 V – 110 150 ns
Switching Minimum On-Time tONmin –110 150 ns
Selected On-Time tON VIN = 24 V, VOUT = 12 V, RON = 137 kΩ 800 1000 1200 ns
Regulation Comparator and Error Amplifier
Load Current Sense Regulation
Threshold
1VCSREG VCS decreasing, SW turns on 187.5 200 210 mV
Load Current Sense Bias Current ICSBIAS VCS = 0.2 V, EN = low – 0.9 – µA
Internal Linear Regulator
VCC Regulated Output VCC 0 mA < ICC < 5 mA, VIN > 6 V 5.1 5.4 5.7 V
VCC Current Limit
2ICCLIM VIN = 24 V, VCC = 0 V 5 20 – mA
Enable Input
Logic High Voltage VIH VEN increasing 1.8 – – V
Logic Low Voltage VIL VEN decreasing – – 0.4 V
EN Pin Pull-down Resistance RENPD VEN = 5 V – 100 – kΩ
Maximum PWM Dimming Off-Time tPWML
Measured while EN = low, during dimming
control, and internal references are powered-on
(exceeding tPWML results in shutdown)
10 17 – ms
Thermal Shutdown
Thermal Shutdown Threshold TSD – 165 – °C
Thermal Shutdown Hysteresis TSDHYS – 25 – °C
1 In test mode, a ramp signal is applied at CS pin to determine the CS pin regulation threshold voltage. In actual application, the average CS pin
voltage is regulated at VCSREG regardless of ripple voltage.
2 The internal linear regulator is not designed to drive an external load
Automotive-Grade, Constant-Current
PWM Dimmable Buck Regulator LED Driver
A6213 and
A6213-1
5
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Characteristic Performance
Panel 1B. VIN = 24 V
Panel 1C. VIN = 30 V
Panel 1A. VIN = 19 V
t
C1,C2
C3
C4
VIN
VOUT
iLED
VEN
Figure 1: Startup waveforms from off-state at various input voltages; note that the rise time of the LED current depends on input/output
voltages, inductor value, and switching frequency
• Operating conditions: LED voltage = 15 V, LED current = 1.3 A, R1 = 63.4 kΩ (frequency = 1 MHz in steady state),
VIN = 19 V (panel 1A), 24 V (panel 1B) and 30 V (panel 1C)
• Oscilloscope settings: CH1 (Red) = VIN (10 V/div), CH2 (Blue) = VOUT (10 V/div),
CH3 (Green) = iLED (500 mA/div), CH4 (Yellow) = Enable (5 V/div), time scale = 50 µs/div
t
C1,C2
C3
C4
VIN
VOUT
iLED
VEN
t
C1,C2
C3
C4
VIN
VOUT
iLED
VEN
Automotive-Grade, Constant-Current
PWM Dimmable Buck Regulator LED Driver
A6213 and
A6213-1
6
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
t
t
Figure 2: PWM operation at various duty cycles; note that there is no startup delay during PWM dimming operation
• Operating conditions: at 200 Hz, VIN = 24 V, VOUT = 15 V, R1 = 63.4 kΩ, duty cycle = 50% (panel 2A) and 2% (panel 2B)
• CH1 (Red) = VIN (10 V/div), CH2 (Blue) = VOUT (10 V/div),
CH3 (Green) = iLED (500 mA/div), CH4 (Yellow) = Enable (5 V/div), time scale = 1 ms/div (panel 2A) and 50 µs/div (panel 2B)
Panel 2A. Duty cycle = 50% and time scale = 1 ms/div
Panel 2B. Duty cycle = 2% and time scale = 50 µs/div
C1,C2
C1,C2
C3
C3
C4
C4
VIN
VIN
VOUT
VOUT
iLED
iLED
VEN
VEN
Automotive-Grade, Constant-Current
PWM Dimmable Buck Regulator LED Driver
A6213 and
A6213-1
7
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
95
90
85
80
75
70
0 0.5 1.0 1.5 2.0 2.5 3.0
Efficiency, η (%)
LED Current, i
LED
(A)
V
IN
= 24 V, V
OUT
= 15 V
V
IN
= 12 V, V
OUT
= 5.5 V
V
IN
= 12 V, V
OUT
= 3.5 V
95
90
85
80
75
70
0 0.5 1.0 1.5 2.0 2.5 3.0
Efficiency, η (%)
LED Current, i
LED
(A)
f
SW
= 500 kHz
f
SW
= 1 MHz
f
SW
= 2 MHz
1
0.1
0.01
0.001
0.1 1001 10
Duty Cycle (%)
LED Current (A)
iLED = 3 A
iLED = 2 A
iLED = 1.4 A
Figure 3: Efficiency versus LED Current at various LED voltages
Operating conditions: fSW = 1 MHz
Figure 4: Efficiency versus LED Current at various switching
frequencies. Operating conditions: VIN = 12 V, VOUT = 5.5 V
Figure 5. Average LED Current versus PWM dimming percentage
Operating conditions: VIN = 12 V, VOUT = 3.5 V, fSW = 1 MHz, fPWM = 200 Hz, L = 10 µH
Automotive-Grade, Constant-Current
PWM Dimmable Buck Regulator LED Driver
A6213 and
A6213-1
8
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
The A6213 is a buck regulator designed for driving a high-current
LED string. It utilizes average current mode control to maintain
constant LED current and consistent brightness. The LED current
level is easily programmable by selection of an external sense
resistor, with a value determined as follows:
iLED = VCSREG / RSENSE
where VCSREG = 0.2 V typical.
Switching Frequency
The A6213 operates in fixed on-time mode during switching. The
on-time (and hence switching frequency) is programmed using
an external resistor connected between the VIN and TON pins, as
given by the following equation:
tON = k × (RON + RINT ) × ( VOUT / VIN )
fSW = 1 / [ k × (RON + RINT )]
where k = 0.0139, with fSW in MHz, tON in µs, and RON and RINT
(internalresistance,5kΩ)inkΩ(seefigure6).
Enable and Dimming
The IC is activated when a logic high signal is applied to the EN
(enable) pin. The buck converter ramps up the LED current to a
target level set by RSENSE.
When the EN pin is forced from high to low, the buck converter
is turned off, but the IC remains in standby mode for up to 10 ms.
If EN goes high again within this period, the LED current is
turned on immediately. Active dimming of the LED is achieved
by sending a PWM (pulse-width modulation) signal to the EN
pin. The resulting LED brightness is proportional to the duty cycle
( tON
/Period)ofthePWMsignal.ApracticalrangeforPWMdim-
ming frequency is between 100 Hz (Period = 10 ms) and 2 kHz.
At a 200 Hz PWM frequency, the dimming duty cycle can be
varied from 100% down to 1% or lower.
If EN is low for more than 17 ms, the IC enters shutdown mode
to reduce power consumption. The next high signal on EN will
initialize a full startup sequence, which includes a startup delay
of approximately 130 µs. This startup delay is not present during
PWM operation.
The EN pin is high-voltage tolerant and can be directly connected
to a power supply. However, if EN is higher than the VIN voltage
Functional Description
Figure 6: Switching Frequency versus RTON Resistance
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
0 20 40 60 80 100 120 140 160 180 200 220 240 260
fsw (MHz)
R
TON
(kΩ)
• During SW on-time:
iRIPPLE = [(VIN –
VOUT) / L] × tON = [(VIN –
VOUT) / L] × T × D
iRIPPLE = [(VOUT –
VD) / L] × tOFF = [(VOUT –
VD) / L] × T × (1 – D)
VOUT =
VIN × D –
VD × (1 – D)
VOUT =
(
VIN – Iav × RDS(on)
) × D –
VD × (1 – D) –
RL × Iav
where D = tON / T.
• During SW off-time:
Therefore (simplified equation for Output Voltage):
More precisely:
Where RL is the resistance fo the inductor.
If VD << VOUT
, then VOUT ≈ VIN × D.
VSW
iL
t
t
VIN
i(max)
iav
i(min)
0
iRIPPLE
tON tOFF
T
–VD
CIN
VIN A6213
SW VOUT
RSENSE
L
iL
MOS
D
Figure 7: Simplified buck controller equations
Automotive-Grade, Constant-Current
PWM Dimmable Buck Regulator LED Driver
A6213 and
A6213-1
9
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Figure 8: Minimum and Maximum Output Voltage versus
Switching Frequency (VIN = 24 V, iLED = 2 A, minimum tON and
tOFF = 150 ns)
Figure 9: Minimum and Maximum Output Voltage versus iLED
current (VIN = 9 V, fSW = 1 MHz, minimum tON and tOFF = 150 ns)
atanytime,aseriesresistor(1kΩ)isrequiredtolimitthecurrent
flowing into the EN pin. This series resistor is not necessary if
EN is driven from a logic input.
PWM Dimming Ratio
The brightness of the LED string can be reduced by adjusting the
PWM duty cycle at the EN pin as follows:
Dimming ratio = PWM on-time / PWM period
For example, by selecting a PWM period of 5 ms (200 Hz PWM
frequency) and a PWM on-time of 50 µs, a dimming ratio of 1%
can be achieved.
In an actual application, the minimum dimming ratio is deter-
mined by various system parameters, including: VIN
, VOUT
,
inductance, LED current, switching frequency, and PWM
frequency. As a general guideline, the minimum PWM on-time
should be kept at 50 µs or longer. A shorter PWM on-time is
acceptable under more favorable operating conditions.
Output Voltage and Duty Cycle
Figure 7 provides simplified equations for approximating output
voltage. Essentially, the output voltage of a buck converter is
approximately given as:
VOUT = VIN × D – VD1 × (1 – D ) ≈ VIN × D, if VD1<< V IN
D = tON / (tON + tOFF )
where D is the duty cycle, and VD1 is the forward drop of the
Schottky diode D1 (typically under 0.5 V).
Minimum and Maximum Output Voltages
For a given input voltage, the maximum output voltage depends
on the switching frequency and minimum tOFF . For example, if
tOFF(min) = 150 ns and fSW = 1 MHz, then the maximum duty
cycle is 85%. So for a 24 V input, the maximum output is 20.3 V.
This means up to 6 LEDs can be operated in series, assuming
Vf = 3.3 V or less for each LED.
The minimum output voltage depends on minimum tON and
switching frequency. For example, if the minimum tON = 150 ns
and fSW = 1 MHz, then the minimum duty cycle is 15%. That
means with VIN = 24 V, the minimum VOUT = 3.2 V (one LED).
To a lesser degree, the output voltage is also affected by other
factors such as LED current, on-resistance of the high-side
switch, DCR of the inductor, and forward drop of the low-side
diode. The more precise equation is shown in figure 7.
As a general rule, switching at lower frequencies allows a wider
range of VOUT , and hence more flexible LED configurations.
This is shown in figure 8.
Figure 8 shows how the minimum and maximum output volt-
ages vary with LED current (assuming RDS(on)=0.4Ω,inductor
DCR=0.1Ω,anddiodeVf = 0.6 V).
If the required output voltage is lower than that permitted by the
minimum tON , the controller will automatically extend the tOFF ,
in order to maintain the correct duty cycle. This means that the
switching frequency will drop lower when necessary, while the
LED current is kept in regulation at all times.
24
22
20
18
16
14
12
10
8
6
4
2
0
0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
VOUT ( V )
fsw (MHz)
V
OUT
(max) (V)
V
OUT
(min) (V)
9
8
7
6
5
4
3
2
1
0
0 0.5 1.0 1.5 2.0 2.5 3.0
VOUT ( V )
iLED (A)
V
OUT
(max) (V)
V
OUT
(min) (V)
Automotive-Grade, Constant-Current
PWM Dimmable Buck Regulator LED Driver
A6213 and
A6213-1
10
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Thermal Budgeting
The A6213 is capable of supplying a 3 A current through its high-
side switch (1.5 A for A6213-1). However, depending on the duty
cycle, the conduction loss in the high-side switch may cause the
package to overheat. Therefore care must be taken to ensure the
total power loss of package is within budget. For example, if the
maximum temperature rise allowed is ∆T = 50 K at the device
case surface, then the maximum power dissipation of the IC is
1.4 W. Assuming the maximum RDS(on)=0.4Ωandadutycycle
of 85%, then the maximum LED current is limited to 2 A approx-
imately. At a lower duty cycle, the LED current can be higher.
Fault Handling
The A6213 is designed to handle the following faults:
• Pin-to-ground short
• Pin-to-neighboring pin short
• Pin open
• External component open or short
•OutputshorttoGND
The waveform in Figure 10 illustrates how the A6213 responds
in the case in which the current sense resistor or the CS pin is
shortedtoGND.NotethattheSWpinovercurrentprotectionis
tripped at around 4 A, and the part shuts down immediately. The
part then goes through startup retry after approximately 380 µs of
cooldown period.
The A6213-1 has the same protection mechanism, except its
Figure 10: A6213 overcurrent protection tripped in the case of a
fault caused by the sense resistor pin shorted to ground; shows
switch node, VSW (ch1, 10 V/div.), output voltage, VOUT (ch2, 10
V/div.), LED current, iLED (ch3, 1 A/div.), t = 100 µs/div.
Figure 12: Startup waveform with a missing Schottky diode;
shows Enable, VEN (ch1, 5 V/div.), swtich node, VSW (ch2, 5 V/
div.), output voltage, VOUT (ch3, 5 V/div.), LED current, iLED (ch4,
500 mA/div.), t = 100 µs/div.
t
C1
C3
C2
VSW
VOUT
iLED
Figure 11: A6313-1 during fault condition where the sense
resistor or CS pin is shorted to GND. Note that its overcurrent
protection threshold is set lower than that of the A6213. Ch1 =
VOUT (5 V/div), Ch2 = i_LED (500 mA/div), t = 200 µs/div.
t
C1
C3
C4
C2
VSW
VEN
Negative voltage
developed at SW pin
during off-time
VOUT
iLED
A6213-1 tripped SW_ILIM at ~2.4 A
overcurrent threshold is 2.2 A. This reduces the risk of inductor
saturation or LED damage during a fault.
As another example, the waveform in Figure 12 shows the fault
case where external Schottky diode D1 is missing or open. As
LED current builds up, a larger-than-normal negative voltage is
developed at the SW node during off-time. This voltage trips the
missing Schottky detection function of the IC. The IC then shuts
down immediately, and waits for a cool-down period before retry.
Cool-down
period
~ 380 µs
i_LED
VOUT
Sense Resistor
shorted during
normal operation
C1
C2
t
Automotive-Grade, Constant-Current
PWM Dimmable Buck Regulator LED Driver
A6213 and
A6213-1
11
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Component Selections
The inductor is often the most critical component in a buck con-
verter. Follow the procedure below to derive the correct param-
eters for the inductor:
1. Determine the saturation current of the inductor. This can be
done by simply adding 20% to the average LED current:
iSAT ≥ iLED × 1.2.
2. Determine the ripple current amplitude (peak-to-peak value). As
a general rule, ripple current should be kept between 10% and
30% of the average LED current:
0.1 < iRIPPLE(pk-pk) / iLED < 0.3.
3. Calculate the inductance based on the following equations:
L = (VIN – VOUT
) × D × T / iRIPPLE , and
D = (VOUT + VD1
) / ( VIN + VD1 ) ,
where
D is the duty cycle,
Tistheperiod1/fSW , and
VD1 is the forward voltage drop of the Schottky diode
D1 (see figure 7).
Inductor Selection Chart
The chart in Figure 13 summarizes the relationship between
LED current, switching frequency, and inductor value. Based on
this chart: Assuming LED current = 2 A and fSW =1 MHz, then
VIN
SW
D1
LED+
LED–
L1
CS
. . .
Iripple
Vripple Vripple
RSENSE
VIN
SW
D1
LED+
LED–
L1
CS
C1
. . .
Iripple
RSENSE
Figure 14. Ripple current and voltage, with and without shunt capacitor
Without output capacitor:
Ripple current through LED string is proportional to ripple voltage
at CS pin.
With a small capacitor across LED string:
Ripple current through LED string is reduced, while ripple voltage
at CS pin remains high.
Figure 13: Inductance selection based on ILED and fSW ;
VIN = 24 V, VOUT = 12 V, ripple current = 30%
0
0.0 0.5 1.0 1.5 2.0 2.5 3.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
Switching Frequency, f SW
(MHz)
LED Current, ILED (A)
L=15 µH
L=22 µH
L=33 µH
L=47 µH
L=10 µH
the minimum inductance required is L = 10 µH in order to keep
the ripple current at 30% or lower. (Note: VOUT = VIN /2isthe
worst case for ripple current). If the switching frequency is lower,
then either a larger inductance must be used, or the ripple current
requirement has to be relaxed.
Automotive-Grade, Constant-Current
PWM Dimmable Buck Regulator LED Driver
A6213 and
A6213-1
12
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Figure 15: Waveforms showing the effects of adding a small filter capacitor across the LED string
• Operating conditions: at 200 Hz, VIN = 24 V, VOUT = 15 V, fSW = 500 kHz, L = 10 µH, duty cycle = 50%
• CH1 (Red) = VIN (10 V/div), CH2 (Blue) = VOUT (10 V/div),
CH3 (Green) = iLED (500 mA/div), CH4 (Yellow) = Enable (5 V/div), time scale = 1 ms/div
Panel 15A: Operation without using any output
capacitor across the LED string
Panel 15B: Operation with a 0.68 µF ceramic
capacitor connected across the LED string
t
C1,C2
C3
C4
VIN
VOUT
iLED
VEN
t
C1,C2
C3
C4
VIN
VOUT
iLED
VEN
Additional Notes on Ripple Current
• For consistent switching frequency, it is recommended to
choose the inductor and switching frequency to ensure the induc-
tor ripple current percentage is at least 10% over normal operat-
ing voltage range (ripple current is lowest at lowest VIN).
If ripple current is less than 10%, the switching frequency may
jitter due to insufficient ripple voltage at CS pin. However, the
average LED current is still regulated.
• There is no hard limit on the highest ripple current percentage
allowed. A 60% ripple current is still acceptable, as long as both
the inductor and LEDs can handle the peak current (average cur-
rent × 1.3 in this case). However, care must be taken to ensure
the valley of the inductor ripple current never drops to zero at the
highest input voltage (which implies a 200% ripple current).
• In general, allowing a higher ripple current percentage enables
lower-inductance inductors to be used, which results in smaller
size and lower cost. The only down-side is the core loss of the
inductor increases with larger ripple currents. But this is typically
a small factor.
• If lower ripple current is required for the LED string, one solu-
tion is to add a small capacitor (such as 2.2 µF) across the LED
string from LED+ to LED– . In this case, the inductor ripple cur-
rent remains high while the LED ripple current is greatly reduced.
Output Filter Capacitor
The A6213 is designed to operate without an output filter capaci-
tor, in order to save cost. Adding a large output capacitor is not
recommended.
In some applications, it may be required to add a small filter
capacitor (up to several µF) across the LED string (between
LED+ and LED-) to reduce output ripple voltage and current. It is
important to note that:
• The effectiveness of this filter capacitor depends on many fac-
tors, such as: switching frequency, inductors used, PCB layout,
LED voltage and current, and so forth.
• The addition of this filter capacitor introduces a longer delay
in LED current during PWM dimming operation. Therefore the
maximum PWM dimming ratio is reduced.
• The filter capacitor should NOT be connected between LED+
andGND.Doingsomaycreateinstabilitybecausethecontrol
loop must detect a certain amount of ripple current at the CS pin
for regulation.
Automotive-Grade, Constant-Current
PWM Dimmable Buck Regulator LED Driver
A6213 and
A6213-1
13
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Application Circuit
The application circuit in Figure 16 shows a design for driving
a 15 V LED string at 1.3 A (set by RSENSE
). The switching fre-
quency is 500 kHz, as set by R1. A 0.68 µF ceramic capacitor is
added across the LED string to reduce the ripple current through
the LEDs (as shown in Figure 15B).
LED+
LED–
VIN
TON
EN
CS
SW
BOOT
GND
VCC
A6213
1
2
3
4
8
7
6
5
V
IN
= 24 to 48 V
C1
47 µF
50 V
C2
4.7µF
50V
EN
C4
0.1 µF
R1
140 kΩ
L1
10 µH / 2 A
C5
0.1 µF
R
SENSE
0.15 Ω
GND
D1
60 V / 2 A
C3
0.68 µF
50 V
LED
string
(
≈
15 V)
...
PAD
Figure 16: Application Circuit Diagram
Suggested Components
Symbol Part Number Manufacturer
C1 EMZA500ADA470MF80G United Chemi-Con
C2 UMK316BJ475KL-T Taiyo Yuden
C3 CGA5L2X5R1H684K160AA TDK
L1 NR8040T100M Taiyo Yuden
D1 B250A-13-F Diodes, Inc.
RSENSE RL1632R-R150-F Susumu
VBAT
GND
VIN
100 kΩ
VBAT
12 V
0
LED
Current
1A
0
VBAT pulsed on/off at 200 Hz, with duty cycle
between 1 % and 99%
1
2
3
4
VIN
TON
EN
CS
SW
BOOT
GND
VCC
8
7
6
5
A6213 LED+
LED–
LED
String
(~6 V)
RSENSE
0.2 Ω
Figure 17: PWM Dimming of LED Current by Using Pulsed Power Supply Line
Additional Application Circuits
The following are some application examples to expand the capa-
bility of the A6213:
• Figure 17 shows PWM dimming of LED current by pulsing the
power supply line
• Figure 18 shows analog dimming of LED current by an exter-
nal DC voltage
• Figure 19 shows thermal de-rating of LED current by an NTC
resistor
Automotive-Grade, Constant-Current
PWM Dimmable Buck Regulator LED Driver
A6213 and
A6213-1
14
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
V= 12 V
IN
GND
200 kΩ
25 kΩ 1 kΩ
1
2
3
4
VIN
TON
EN
EN
CS
SW
BOOT
GND
VCC
8
7
6
5
A6213 LED+
LED–
LED
String
(~6 V)
RSENSE
0.2 Ω
R1
C1
47 µF
50 V
C2
4.7 µF
50 V
C4
0.1 µF
C5
0.1 µF
V= 0.2 V
CS
ADIM
ADIM
iADIM
Analog Dimming
Voltage: 0 to 5.2 V
D1
60 V 2A
C3
open
L1
47 µH 2A
V:
SENSE
0.22 V to 0 V
i:
LED
1.04 A to 0A
iLED
i= (0.2 V–i× 1000)/R
LED ADIM SENSE
i= (V – 0.2)/25 k
ADIM ADIM
100%
0
0.2 V5.2 V
Figure 18: Analog Dimming of LED Current with an External DC Voltage
GND
200 kΩ
30 kΩ 1 kΩ
1
2
3
4
VIN
TON
EN
CS
SW
BOOT
GND
VCC
8
7
6
5
A6213 LED+
LED–
LED
String
(~6 V)
RSENSE
0.2 Ω
R1
C1
47 µF
50 V
C2
4.7 µF
50 V
C4
0.1 µF
C5
0.1 µF
V= 0.2 V
CS
V= 5.2 V
CC
i:
ADIM
0.02 mA @ 25ºC
0.096 mA @ 100ºC
NTC:
220 k @ 25ºC
22 k @ 100ºC
D1
60 V 2A
C3
open
L1
47 µH 2A
V:
SENSE
0.18 V @ 25ºC
0.104 V @ 100ºC
i= (0.2 V–i× 1000)/R
LED ADIM SENSE
i= (V – 0.2)/(R + 30 k)
ADIMCC NTC
0.9 A@ 25ºC
0.52 A@ 100ºC
Figure 19: Thermal Foldback of LED Current Using NTC Resistor
Automotive-Grade, Constant-Current
PWM Dimmable Buck Regulator LED Driver
A6213 and
A6213-1
15
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Component Placement and PCB Layout Guidelines
PCB layout is critical in designing any switching regulator. A
good layout reduces emitted noise from the switching device,
and ensures better thermal performance and higher efficiency.
The following guidelines help to obtain a high quality PCB
layout. Figure 20 shows an example for components placement.
Figure 21 shows the three critical current loops that should be
minimized and connected by relatively wide traces.
1) When the upper FET (integrated inside the A6213) is on, cur-
rentflowsfromtheinputsupply/capacitors,throughtheupper
FET, into the load via the output inductor, and back to ground as
shown in loop 1. This loop should have relatively wide traces.
Ideally this connection is made on both the top (component) layer
and via the ground plane.
2) When the upper FET is off, free-wheeling current flows from
ground through the asynchronous diode D1, into the load via the
output inductor, and back to ground as shown in loop 2. This loop
should also be minimized and have relatively wide traces. Ideally
this connection is made on both the top (component) layer and
via the ground plane.
3)Thehighestdi/dtoccursattheinstanttheupperFETturnson
and the asynchronous diode D1 undergoes reverse recovery as
shown in loop 3. The ceramic input capacitors C2 must deliver
this high instantaneous current. C1 (electrolytic capacitor) should
not be too far off C2. Therefore, the loop from the ceramic input
capacitor through the upper FET and asynchronous diode to
ground should be minimized. Ideally this connection is made on
both the top (component) layer and via the ground plane.
4) The voltage on the SW node (pin 8) transitions from 0 V to
VIN very quickly and may cause noise issues. It is best to place
the asynchronous diode and output inductor close to the A6213 to
minimize the size of the SW polygon.
Keep sensitive analog signals (CS, and R1 of switching fre-
quency setting) away from the SW polygon.
6) For accurate current sensing, the LED current sense resistor
RSENSE should be placed close to the IC.
7) Place the boot strap capacitor C4 near the BOOT node (pin 7)
and keep the routing to this capacitor short.
8) When routing the input and output capacitors (C1, C2, and C3
if used), use multiple vias to the ground plane and place the vias
as close as possible to the A6213 pads.
9) To minimize PCB losses and improve system efficiency, the
input (VIN) and output (VOUT) traces should be wide and dupli-
cated on multiple layers, if possible.
Figure 21: Three different current loops in a buck converterFigure 20: Example layout for the A6213 evaluation board
VIN CIN COUT
D1
L1
LED
SW
Loop 2
Loop 1
Loop 3
Automotive-Grade, Constant-Current
PWM Dimmable Buck Regulator LED Driver
A6213 and
A6213-1
16
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
10) Connection to the LED array should be kept short. Exces-
sively long wires can cause ringing or oscillation. When the LED
array is separated from the converter board and an output capaci-
tor is used, the capacitor should be placed on the converter board
to reduce the effect of stray inductance from long wires.
Ø0.3 mm via
Top-layer
exposed copper
Signal traces
LJ package
exposed
thermal pad
LJ package
footprint
0.7 mm
0.7 mm
Figure 22: Suggested PCB layout for thermal optimization (maximum
available bottom-layer copper recommended)
Thermal Dissipation
The amount of heat that can pass from the silicon of the A6213
to the surrounding ambient environment depends on the thermal
resistance of the structures connected to the A6213. The thermal
resistance, RθJA
, is a measure of the temperature rise created by
power dissipation and is usually measured in degrees Celsius per
watt(°C/W).
Thetemperaturerise,ΔT,iscalculatedfromthepowerdissipated,
PD
, and the thermal resistance, RθJA
, as:
 ΔT = PD × RθJA
A thermal resistance from silicon to ambient, RθJA
, of approxi-
mately35°C/WcanbeachievedbymountingtheA6213ona
standard FR4 double-sided printed circuit board (PCB) with a
copper area of a few square inches on each side of the board
under the A6213. Additional improvements in the range of 20%
may be achieved by optimizing the PCB design.
Optimizing Thermal Layout
The features of the printed circuit board, including heat conduc-
tion and adjacent thermal sources such as other components,
have a very significant effect on the thermal performance of the
device. To optimize thermal performance, the following should
be taken into account:
• The device exposed thermal pad should be connected to as
much copper area as is available.
• Copper thickness should be as high as possible (for example,
2 oz. or greater for higher power applications).
• The greater the quantity of thermal vias, the better the dissipa-
tion. If the expense of vias is a concern, studies have shown
that concentrating the vias directly under the device in a tight
pattern, as shown in Figure 22, has the greatest effect.
• Additional exposed copper area on the opposite side of the
board should be connected by means of the thermal vias. The
copper should cover as much area as possible.
• Other thermal sources should be placed as remote from the
device as possible
• Place as many vias as possible to the ground plane around the
anode of the asynchronous diode.
Automotive-Grade, Constant-Current
PWM Dimmable Buck Regulator LED Driver
A6213 and
A6213-1
17
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
3.30
2
1
8
C
1.27
5.60
2.41
1.75
0.65
2.41 NOM
3.30 NOM
SEATING
PLANE
1.27 BSC A
B
C
B
21
8
C
SEATING
PLANE
C0.10
8X
0.25 BSC
1.04 REF
1.70 MAX
4.90 ±0.10
3.90 ±0.10 6.00 ±0.20
0.51
0.31 0.15
0.00
0.25
0.17
1.27
0.40
8°
0°
A
Branded Face
For Reference Only; not for tooling use (reference MS-012BA)
Dimensions in millimeters
Dimensions exclusive of mold flash, gate burrs, and dambar protrusions
Exact case and lead configuration at supplier discretion within limits shown
Terminal #1 mark area
Exposed thermal pad (bottom surface); dimensions may vary with device
Reference land pattern layout (reference IPC7351 SOIC127P600X175-9AM);
all pads a minimum of 0.20 mm from all adjacent pads; adjust as necessary
to meet application process requirements and PCB layout tolerances; when
mounting on a multilayer PCB, thermal vias at the exposed thermal pad land
can improve thermal dissipation (reference EIA/JEDEC Standard JESD51-5)
PCB Layout Reference View
SEATING PLANE
GAUGE PLANE
Package LJ, 8-Pin Narrow SOIC
with Exposed Thermal Pad
Automotive-Grade, Constant-Current
PWM Dimmable Buck Regulator LED Driver
A6213 and
A6213-1
18
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
For the latest version of this document, visit our website:
www.allegromicro.com
Revision History
Revision Revision Date Description of Revision
1 October 21, 2013 Updated Tstg.
2 March 27, 2014 Revised VCC Spec and Suggested Components Table.
3 April 25, 2014 Added new Figure 11.
4 December 31, 2014 Added new application circuit diagrams.
5 January 29, 2016 Revised VCC Absolute Maximum Rating from 14 to 7 V.
6 March 17, 2016 Added Load Current Sense Regulation Threshold footnote (page 4); updated Additional Notes on
Ripple Current (page 12).
Copyright ©2016, Allegro MicroSystems, LLC
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permit improvements in the performance, reliability, or manufacturability of its products. Before placing an order, the user is cautioned to verify that
the information being relied upon is current.
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