1
LTC1928-5
, LTC and LT are registered trademarks of Linear Technology Corporation
ThinSOT is a trademark of Linear Technology Corporation.
FEATURES
APPLICATIO S
U
DESCRIPTIO
U
TYPICAL APPLICATION
U
■
Low Output Noise: 90
µ
V
RMS
(100kHz BW)
■
Fixed Output Voltage: 5V
■
Input Voltage Range: 2.7V to 4.4V
■
No Inductors Required
■
Uses Small Ceramic Capacitors
■
Output Current Up to 30mA
■
550kHz Switching Frequency
■
Low Operating Current: 190µA
■
Low Shutdown Current: 4µA
■
Internal Thermal Shutdown and Current Limiting
■
Low Profile (1mm) ThinSOT
TM
Package
The LTC
®
1928-5 is a doubler charge pump with an internal
low noise, low dropout (LDO) linear regulator. The part is
designed to provide a low noise boosted supply voltage for
powering noise sensitive devices such as high frequency
VCOs in wireless applications.
An internal charge pump converts a 2.7V to 4.4V input to
a boosted output, while the internal LDO regulator con-
verts the boosted voltage to a low noise regulated output.
The regulator is capable of supplying up to 30mA of output
current. Shutdown reduces the supply current to <8µA,
removes the load from V
IN
by disabling the regulator and
discharges V
OUT
to ground through a 200Ω switch.
The LTC1928-5 LDO regulator is stable with only 2µF on
the output. Small ceramic capacitors can be used, reduc-
ing PC board area.
The LTC1928-5 is short-circuit and overtemperature pro-
tected. The part is available in a 6-pin low profile
(1mm)ThinSOT package.
■
VCO Power Supplies for Cellular Phones
■
2-Way Pagers
■
Wireless PCMCIA Cards
■
Portable Medical Instruments
■
Low Power Data Acquisition
■
Remote Transmitters
■
White LED Drivers
■
GaAs Switches
Figure 1. Low Noise 5V Power Supply
Doubler Charge Pump with
Low Noise Linear Regulator
in ThinSOT
Output Noise (BW = 10Hz to 2.5MHz)
VOUT
200µV/DIV
CCPO = COUT = 4.7µF 100µs/DIV 19285 TA01
IOUT = 10mA
VIN = 3V
VOUT = 5V
TA = 25°C
1
5
6
3
4
2
V
OUT
CPO
GND
V
IN
2.7V TO 4.4V V
IN
CP
CN/SHDN
5V
4.7µF
0.47µF4.7µF
4.7µF
19285 F01
V
OUT
LTC1928-5
2
LTC1928-5
T
JMAX
= 125°C, θ
JA
= 230°C/W
ORDER PART
NUMBER
V
IN
to Ground ..............................................–0.3V to 5V
V
OUT
Voltage...........................................–0.3V to 5.25V
CPO to Ground ........................................................ 10V
CN/SHDN to Ground ..................... –0.3V to (V
IN
+ 0.3V)
V
OUT
Short-Circuit Duration............................. Indefinite
I
OUT .........................................................................................
40mA
Operating Temperature Range (Note 2) ...–40°C to 85°C
Maximum Junction Temperature ......................... 125°C
Storage Temperature Range ................. –65°C to 150°C
Lead Temperature (Soldering, 10 sec)..................300°C
(Note 1)
Consult factory for parts specified with wider operating temperature ranges.
1
2
3
V
IN
GND
V
OUT
6
5
4
CN/SHDN
CP
CPO
TOP VIEW
S6 PACKAGE
6-LEAD PLASTIC SOT-23
S6 PART MARKING
LTKT
PARAMETER CONDITIONS MIN TYP MAX UNITS
V
IN
Operating Voltage ●2.7 4.4 V
I
VIN
Shutdown Current SHDN = 0V (Note 5) ●48 µA
I
VIN
Operating Current I
OUT
= 0mA, Burst Mode
TM
Operation ●190 330 µA
Regulated Output Voltage I
OUT
= 1mA ●4.9 5 5.1 V
V
OUT
Temperature Coefficient ±50 ppm
Charge Pump Oscillator Frequency I
OUT
> 500µA, V
IN
= 2.7V to 4.4V ●480 550 620 kHz
CPO Output Resistance V
IN
= 2.7V, I
OUT
= 10mA ●17 30 Ω
V
IN
= 4.4V, I
OUT
= 10mA ●14 24 Ω
V
OUT
Dropout Voltage (Note 3) I
OUT
= 10mA, V
OUT
= 5V ●100 mV
V
OUT
Enable Time R
LOAD
= 2k 0.6 ms
V
OUT
Output Noise Voltage I
OUT
= 10mA, 10Hz ≤ f ≤ 100kHz 90 µV
RMS
I
OUT
= 10mA, 10Hz ≤ f ≤ 2.5MHz 800 µV
P-P
V
OUT
Line Regulation V
IN
= 2.7V to 4.4V, I
OUT
= 0 ●420 mV
V
OUT
Load Regulation I
OUT
= 1mA to 10mA ●210 mV
I
OUT
= 1mA to 30mA (Note 4) 4 mV
V
OUT
Shutdown Resistance CN/SHDN = 0V (Note 5)
V
IN
= 2.7V, Resistance Measured to Ground ●160 400 Ω
V
IN
= 4.4V, Resistance Measured to Ground ●100 300 Ω
CN/SHDN Input Threshold V
IN
= 2.7V to 4.4V (Note 5) ●0.15 0.5 1.6 V
CN/SHDN Input Current CN/SHDN = 0V (Note 5) ●–1 –3 –6 µA
Burst Mode is a trademark of Linear Technology Corporation.
LTC1928ES6-5
ABSOLUTE AXI U RATI GS
WWWU
PACKAGE/ORDER I FOR ATIO
UU
W
ELECTRICAL CHARACTERISTICS
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: The LTC1928ES6-5 is guaranteed to meet performance
specifications from 0°C to 70°C. Specifications over the –40°C to 85°C
operating temperature range are assured by design, characterization and
correlation with statistical process controls.
Note 3: Dropout voltage is the minimum input/output voltage required to
maintain regulation at the specified output current. In dropout the output
voltage will be equal to: V
CPO
– V
DROPOUT
(see Figure 2).
The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25°C.
VIN = 3V, CFLY = 0.47µF, COUT, CCPO, CIN = 4.7µF unless otherwise specified.
3
LTC1928-5
Note 5: CN/SHDN must be driven with a source impedance of at least
100Ω (R
SOURCE
) to prevent damage to the part. This pin is multiplexed
and may be connected through a low switch impedance to V
IN
. There may
be a large amount of current (V
IN
/R
SOURCE
) until the shutdown state
occurs after which the charge pump switches at CN/SHDN become high
impedance and the current will fall to <8µA.
CPO Output Resistance vs VIN Min and Max VCPO vs VIN VOUT Transient Response
Note 4: Operating conditions are limited by maximum junction
temperature. The regulated output specification will not apply for all
possible combinations of input voltage and output current. When
operating at maximum input voltage, the output current range may be
limited. When operating at maximum output current, the input voltage
range may be limited.
Shutdown to Enable Timing
(Figure 5) Enable to Shutdown Timing
(Figure 5)
V
IN
(V)
R
CPO
(Ω)
35
30
25
20
15
10
52.5 3.0 3.5
19285 G01
4.0 4.5
T
A
= 25°C
C
FLY
= 0.47µF
I
OUT
= 10mA
V
IN
(V)
V
CPO
(V)
9
8
7
6
5
4
3
2.5 3.0 3.5
19285 G02
4.0 4.5
(A)
(A) THE MAXIMUM GENERATED NO LOAD
CPO VOLTAGE
(B) THE MINIMUM ALLOWABLE CPO VOLTAGE,
AT FULL LOAD, TO ENSURE THAT THE LDO
IS NOT DISABLED
(B)
V
CPO
= 1.45(V
IN
)
V
CPO
= 2(V
IN
)
T
A
= 25°C
TIME (µs)
050
∆V
OUT
(mV)I
OUT
(mA)
100 200150 250 300
19285 G03
10
5
0
–5
–10
15
10
5
0
T
A
= 25°C
V
IN
= 3V
V
OUT
= 5V
C
OUT
= 4.7µF
200µs/DIV
SHDN (V)V
OUT
(V)
2
0
5
4
3
2
1
0
19285 G04
T
A
= 25°C
V
IN
= 3V
V
OUT
= 5V
I
OUT
= 10mA
C
OUT
= C
CPO
= 4.7µF
1ms/DIV
SHDN (V)V
OUT
(V)
2
0
5
4
3
2
1
0
19285 G05
NO LOAD
T
A
= 25°C
V
IN
= 3V
V
OUT
= 5V
C
OUT
= 4.7µF
ELECTRICAL CHARACTERISTICS
VOUT Voltage vs Temperature
TEMPERATURE (°C)
–50
5.040
5.030
5.020
5.010
5.000
4.990
4.980 25 75
19285 G06
–25 0 50 100 125
V
OUT
VOLTAGE (V)
V
IN
= 3V
I
OUT
= 10mA
TYPICAL PERFOR A CE CHARACTERISTICS
UW
4
LTC1928-5
Operating Current vs VIN
(No Load)
BLOCK DIAGRA
W
–
+
–
+
CHARGE PUMP
AND
SLEW CONTROL
5
1
6
2
3
4
CN/SHDN
CP
CLK B ENB
CPO
V
OUT
V
IN
C
FLY
0.47µF
C
CPO
4.7µF
C
OUT
4.7µF
POR/
SHDN
CONTROL
550kHz
OSCILLATOR
SD
BURST
V
REF
= 1.235V
–
+
C
IN
4.7µF
SD
GND
19285 BD
160Ω
V
IN
(V)
OPERATING CURRENT (µA)
260
240
220
200
180
160
140
120
100
19285 G07
2.5 3.0 3.5 4.0 4.5
T
A
= 25°C
Efficiency vs Supply Voltage
SUPPLY VOLTAGE (V)
2.6
40
EFFICIENCY (%)
50
70
80
90
3.0 3.4 3.6 4.4
19285 G08
60
2.8 3.2 3.8 4.0 4.2
100 T
A
= 25°C
I
OUT
= 15mA
C
FLY
= 0.47µF
Output Voltage vs Output Current
OUTPUT CURRENT (mA)
0
OUTPUT VOLTAGE (V)
35 40
19285 G09
51015
20 25 30
4.901
4.900
4.989
4.988
4.987
4.986
4.985
4.984
4.983
4.982
T
A
= 25°C
V
IN
= 3V
C
FLY
= 0.47µF
TYPICAL PERFOR A CE CHARACTERISTICS
UW
5
LTC1928-5
V
IN
(Pin 1): Input Voltage, 2.7V to 4.4V. V
IN
should be
bypassed with a ≥2µF low ESR capacitor as close to the
pin as possible for best performance. A minimum capaci-
tance value of 0.1µF is required.
GND (Pin 2): System Ground.
V
OUT
(Pin 3): Low Noise Regulated Output Voltage. V
OUT
should be bypassed with a ≥2µF low ESR capacitor as
close to the pin as possible for best performance. The V
OUT
voltage is internally set to 5V.
PIN FUNCTIONS
UUU
CPO (Pin 4): Boosted Unregulated Voltage. Approxi-
mately 1.95V
IN
at low loads. Bypass with a ≥2µF low ESR
capacitor.
CP (Pin 5): Flying Capacitor Positive Input.
CN/SHDN (Pin 6): Flying Capacitor Negative Input and
SHDN. When this pin is pulled to ground through a 100Ω
resistor, the part will go into shutdown within approxi-
mately 30µs.
Operation
The LTC1928-5 uses a switched-capacitor charge pump
to generate a CPO voltage of approximately 2V
IN
. CPO
powers an internal low dropout linear regulator that sup-
plies a regulated output at V
OUT
. Internal comparators are
used to sense CPO and V
IN
voltages for power-up condi-
tioning. The output current is sensed to determine the
charge pump operating mode. A trimmed internal bandgap
is used as the voltage reference and a trimmed internal
oscillator is used to control the charge pump switches.
The charge pump is a doubler configuration that uses one
external flying capacitor. When enabled, a 2-phase
nonoverlapping clock controls the charge pump switches.
At start-up, the LDO is disabled and the load is removed
from CPO. When CPO reaches 1.75V
IN
the LDO is enabled.
If CPO falls below 1.45V
IN
the LDO will be disabled. Gen-
erally, the charge pump runs open loop with continuous
clocking for low noise. If CPO is greater than 1.95V
IN
and
I
OUT
is less than 200µA, the charge pump will operate in
Burst Mode operation for increased efficiency but slightly
higher output noise. In Burst Mode operation, the clock is
disabled when CPO reaches 1.95V
IN
and enabled when
CPO droops by about 150mV. The switching frequency is
precisely controlled to ensure that the frequency is above
455kHz and at the optimum rate to ensure maximum effi-
ciency. The switch edge rates are also controlled to mini-
mize noise. The effective output resistance at CPO is
dependent on the voltage at V
IN
, CPO, the flying capacitor
value C
FLY
and the junction temperature. A low ESR ca-
pacitor of ≥2µF should be used at CPO for minimum noise.
APPLICATIONS INFORMATION
WUUU
The LDO is used to filter the ripple on CPO and to set an
output voltage independent of CPO. V
OUT
is set by an
internal reference and resistor divider. The LDO requires a
capacitor on V
OUT
for stability and improved load transient
response. A low ESR capacitor of ≥2µF should be used.
Maximum I
OUT
Calculations
The maximum available current can be calculated based
on the open circuit CPO voltage, the dropout voltage of the
LDO and the effective output resistance of the charge
pump. The open circuit CPO voltage is approximately 2V
IN
(see Figure 2).
Example:
V
IN
= 3V
V
OUT
= 5V
R
CPO
= 30Ω
Maximum unloaded CPO voltage = 2V
IN
= 6V
V
DROPOUT(MAX)
= 100mV
I
OUT(MAX)
= (2V
IN
– V
DROPOUT(MAX)
– V
OUT
)/R
CPO
= (6V – 0.1V – 5V)/30Ω = 30mA
V
CPO
must be greater than 1.45V
IN
= 4.35V. To confirm
this, calculate V
CPO
:
V
CPO
= 6V – (30mA • 30Ω) = 5.1V
For minimum noise applications the LDO must be kept out
of dropout to prevent CPO noise from coupling into V
OUT
.
6
LTC1928-5
APPLICATIONS INFORMATION
WUUU
External CPO Loading
The CPO output can drive an external load (for example, an
LDO). The current required by this additional load will
reduce the available current from V
OUT
. If the external load
requires 1mA, the available current at V
OUT
will be reduced
by 1mA.
Short-Circuit and Thermal Protection
V
OUT
can be shorted to ground indefinitely. Internal cir-
cuitry will limit the output current. If the junction tempera-
ture exceeds 150°C the part will shut down. Excessive
power dissipation due to heavy loads will also cause the
part to shut down when the junction temperature exceeds
150°C. The part will become enabled when the junction
temperature drops below 140°C. If the fault conditions
remain in place, the part will cycle between the shutdown
and enabled states.
Capacitor Selection
For best performance it is recommended that low ESR
ceramic capacitors be used to reduce noise and ripple.
C
OUT
must be ≥2µF and C
CPO
must be equal to or greater
than C
OUT
. C
IN
is dependent on the input power supply
source impedance. The charge pump demands large
instantaneous currents which may induce ripple onto a
common voltage rail. C
IN
should be ≥2µF and a spike
reducing resistor of 2.2Ω may be required between V
IN
and the supply.
+–
+
–
R
CPO
R
DROPOUT
V
DROPOUT
C
CPO
V
CPO
V
OUT
I
OUT
19285 F02
2V
IN
Figure 2. Equivalent Circuit
A low ESR ceramic capacitor is recommended for the
flying capacitor C
FLY
with a value of 0.47µF. At low load or
high V
IN
a smaller capacitor could be used to reduce ripple
on CPO which would reflect as lower ripple on V
OUT
.
If a minimum enable time is required, the CPO output filter
capacitor should be at least 2× the V
OUT
filter capacitor.
When the LDO is first enabled, the CPO capacitor will
dump a large amount of charge into the V
OUT
capacitor. If
the drop in the CPO voltage falls below 1.45V
IN
the LDO
will be disabled and the CPO voltage will be required to
charge up to 1.75V
IN
to enable the LDO. The resulting
cycling extends the enable time.
Output Ripple
The output ripple on CPO includes a spike component
from the charge pump switches and a droop component
which is dependent on the load current and the value of C3.
The charge pump has been carefully designed to minimize
the spike component, however, low ESR capacitors are
essential to reduce the remaining spike energy effect on
the CPO voltage. C
CPO
should be increased for high load
currents to minimize the droop component. Ripple com-
ponents on CPO are greatly reduced at V
OUT
by the LDO,
however, C
OUT
should also be a low ESR capacitor to
improve filtering of the CPO noise.
Shutdown
When CN/SHDN = 0V, the part will be in shutdown, the
supply current will be <8µA and V
OUT
will be shorted to
ground through a 160Ω switch. In addition, CPO will be
high impedance and disconnected from V
IN
and
CN/SHDN.
Shutdown is achieved by internally sampling the
CN/SHDN pin for a low voltage. Time between shutdown
samples is about 30µs. During the sample time the charge
pump switches are disabled and CN/SHDN must be pulled
to ground within 400ns. A resistor value between 100Ω
and 1k is recommended. Parasitic lead capacitance should
be minimized on the CN/SHDN pin.
7
LTC1928-5
APPLICATIONS INFORMATION
WUUU
Power-On Reset
Upon initial power-up, a power-on reset circuit ensures
that the internal functions are correctly initialized. Once
V
IN
reaches about 1V, the power-on reset circuit will
enable the part as long as the CN/SHDN pin is not pulled
low.
Thermal Considerations
The power handling capability of the device will be limited
by the maximum rated junction temperature (125°C). The
device dissipation P
D
= I
OUT
(2V
IN
– V
OUT
) + V
IN
(2mA). The
device dissipates the majority of its heat through its pins,
especially GND (Pin 2). Thermal resistance to ambient can
be optimized by connecting GND to a large copper region
on the PCB, which serves as a heat sink. Applications that
operate the LTC1928-5 near maximum power levels should
maximize the copper area at all pins except CP and
CN/SHDN and ensure that there is some airflow over the
part to carry away excess heat.
General Layout Considerations
Due to the high switching frequency and high transient
currents produced by the device, careful board layout is a
must. A clean board layout using a ground plane and short
connections to all capacitors will improve noise perfor-
mance and ensure proper regulation.
Measuring Output Noise
Measuring the LTC1928 low noise levels requires care.
Figure 3 shows a test setup for taking the measurement.
Good connection and signal handling technique should
yield about 800µV
P-P
over a 2.5MHz bandwidth. The noise
measurement involves AC coupling the LTC1928 output
into the test setup’s input and terminating this connection
with 50Ω. Coaxial connections must be maintained to
preserve measurement integrity.
Figure 3. LTC1928-5 Noise Measurement Test Setup
Figure 4. LTC1928-5, External Load on CPO, No Shutdown State
4
5
6
3
2
1
VOUT
GND
VIN
CPO
CP
CN/SHDN 3.3V
IN
GND
OUT
COUT
4.7µF
CIN
4.7µF
CFLY
0.47µF
5V
VIN
3V
CCPO
4.7µF
10µF
19285 F04
LTC1928-5 ADDITIONAL
LDO
VRIPPLE < 800µVP-P
LTC1928
DEMO
BOARD OSCILLOSCOPE
BANDWIDTH
FILTER
CONNECT BNC AND
R
LOAD
GROUND TO THE
OUTPUT CAPACITOR
GROUND TERMINAL PLACE COUPLING
CAPACITOR IN SHIELDED
BOX WITH COAXIAL
CONNECTOR
COUPLING
CAPACITOR
BNC CABLES
OR COUPLERS
BATTERY OR
LOW NOISE DC
POWER SUPPLY
V
OUT
R
LOAD
R*
R*
*50Ω TERMINATIONS
HP-11048C OR
EQUIVALENT
R*
NOTE: KEEP BNC CONNECTIONS
AS SHORT AS POSSIBLE
PLACE BANDWIDTH FILTER
COMPONENTS IN SHIELDED BOX
WITH COAXIAL CONNECTORS
PREAMP
1822
INPUT
19285 F03
–
+
10×
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
8
LTC1928-5
1928f LT/TP 0601 2K • PRINTED IN USA
LINEAR TECHN OLOGY CORPORATION 2000
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
●
FAX: (408) 434-0507
●
www.linear-tech.com
RELATED PARTS
PART NUMBER DESCRIPTION COMMENTS
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P-P
Typical Ripple, Up to 10mA
LT1611 Inverting 1.4MHz Switching Regulator 5V to –5V at 150mA, Low Output Noise
LT1613 1.4MHz Boost Switching Regulator in ThinSOT 3.3V to 5V at 200mA, Low Noise PWM Operation
LTC1682 Doubler Charge Pump with Low Noise Linear Regulator 60µV
RMS
Noise, I
OUT
up to 80mA, MSOP
LTC1754-5 Micropower 5V Charge Pump in ThinSOT I
Q
= 13µA, I
OUT
to 50mA, Shutdown
LT1761 Series 100mA ThinSOT, Low Noise LDO Regulators 20µA I
Q
, 20µV
RMS
Noise, 300mV Dropout
LTC3200 Constant Frequency Doubler Charge Pump Low Noise, 5V Output or Adjustable
Figure 5. Low Noise 5V Supply with Shutdown
APPLICATIONS INFORMATION
WUUU
3
4
2
1
5
6
V
IN
CP
CN/SHDN
V
OUT
CPO
GND
100Ω
2N7002 SHDN
C
OUT
4.7µF
C
IN
4.7µFC
FLY
0.47µF
5V
V
IN
2.7V TO 4.4V
C
CPO
4.7µF
19285 F05
LTC1928-5 V
RIPPLE
< 800µV
P-P
S6 Package
6-Lead Plastic SOT-23
(Reference LTC DWG # 05-08-1634)
(Reference LTC DWG # 05-08-1636)
PACKAGE DESCRIPTION
U
1.50 – 1.75
(.059 – .069)
(NOTE 3)
2.60 – 3.00
(.102 – .118)
.25 – .50
(.010 – .020)
(6PLCS, NOTE 2)
L
DATUM ‘A’
.09 – .20
(.004 – .008)
(NOTE 2)
A1
S6 SOT-23 0401
2.80 – 3.10
(.110 – .118)
(NOTE 3)
.95
(.037)
REF
AA2
1.90
(.074)
REF
.20
(.008)
.90 – 1.45
(.035 – .057)
.00 – 0.15
(.00 – .006)
.90 – 1.30
(.035 – .051)
.35 – .55
(.014 – .021)
1.00 MAX
(.039 MAX)
A
A1
A2
L
.01 – .10
(.0004 – .004)
.80 – .90
(.031 – .035)
.30 – .50 REF
(.012 – .019 REF)
PIN ONE ID
MILLIMETERS
(INCHES)
NOTE:
1. CONTROLLING DIMENSION: MILLIMETERS
2. DIMENSIONS ARE IN
3. DRAWING NOT TO SCALE
4. DIMENSIONS ARE INCLUSIVE OF PLATING
5. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR
6. MOLD FLASH SHALL NOT EXCEED .254mm
7. PACKAGE EIAJ REFERENCE IS:
SC-74A (EIAJ) FOR ORIGINAL
JEDEL MO-193 FOR THIN
SOT-23
(Original) SOT-23
(ThinSOT)
