LTC1928-5
1
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For more information www.linear.com/LTC 1928-5
Figure 1. Low Noise 5V Power Supply
Output Noise (BW = 10Hz to 2.5MHz)
TYPICAL APPLICATION
FEATURES DESCRIPTION
Doubler Charge Pump with
Low Noise Linear Regulator
in ThinSOT
The LT C
®
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 converts
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 VIN by disabling the regulator and
discharges VOUT 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.
APPLICATIONS
n Low Output Noise: 90µVRMS (100kHz BW)
n Fixed Output Voltage: 5V
n Input Voltage Range: 2.7V to 4.4V
n No Inductors Required
n Uses Small Ceramic Capacitors
n Output Current Up to 30mA
n 550kHz Switching Frequency
n Low Operating Current: 190µA
n Low Shutdown Current: 4µA
n Internal Thermal Shutdown and Current Limiting
n Low Profile (1mm) ThinSOT™ Package
n VCO Power Supplies for Cellular Phones
n 2-Way Pagers
n Wireless PCMCIA Cards
n Portable Medical Instruments
n Low Power Data Acquisition
n Remote Transmitters
n White LED Drivers
n GaAs Switches
L, LT , LT C , LT M , Linear Technology and the Linear logo are registered trademarks and
ThinSOT and Burst Mode are trademarks of Linear Technology Corporation. All other
trademarks are the property of their respective owners.
1
5
6
3
4
2
VOUT
CPO
GND
VIN
2.7V TO 4.4V
VIN
CP
CN/SHDN
5V
4.7µF
0.47µF 4.7µF
4.7µF
19285 F01
V
OUT
LTC1928-5
VOUT
200µV/DIV
19285 TA01
CCPO = COUT = 4.7µF
IOUT = 10mA
VIN = 3V
VOUT = 5A
T
A
= 25°C
100µs/DIV
LTC1928-5
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For more information www.linear.com/LTC 1928-5
PIN CONFIGURATIONABSOLUTE MAXIMUM RATINGS
VIN to Ground ............................................... –0.3V to 5V
VOUT Voltage ........................................... –0.3V to 5.25V
CPO to Ground ..........................................................10V
CN/SHDN to Ground ..................... –0.3V to (VIN + 0.3V)
VOUT Short-Circuit Duration ............................. Indefinite
IOUT ........................................................................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)
1
2
3
VIN
GND
V
OUT
6
5
4
CN/
SHDN
CP
CPO
TOP VIEW
S6 PACKAGE
6-LEAD PLASTIC SOT-23
TJMAX = 125°C, θJA = 230°C/W
ORDER INFORMATION
ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = 3V, CF LY = 0.47µF, COUT, CCPO, CIN = 4.7µF unless otherwise
specified.
LEAD FREE FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE
LTC1928ES6-5#PBF LTC1928ES6-5#TRPBF LTKT 6-Lead Plastic SOT-23 –40°C to 85°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
Consult LTC Marketing for information on nonstandard lead based finish parts.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
PARAMETER CONDITIONS MIN TYP MAX UNITS
VIN Operating Voltage l2.7 4.4 V
IVIN Shutdown Current SHDN = 0V (Note 5) l4 8 µA
IVIN Operating Current IOUT = 0mA, Burst Mode™ Operation l190 330 µA
Regulated Output Voltage IOUT = 1mA l4.9 5 5.1 V
VOUT Temperature Coefficient ±50 ppm
Charge Pump Oscillator Frequency IOUT > 500µA, VIN = 2.7V to 4.4V l480 550 620 kHz
CPO Output Resistance VIN = 2.7V, IOUT = 10mA
VIN = 4.4V, IOUT = 10mA
l
l
17
14
30
24
Ω
Ω
VOUT Dropout Voltage (Note 3) IOUT = 10mA, VOUT = 5V l100 mV
VOUT Enable Time RLOAD = 2k 0.6 ms
VOUT Output Noise Voltage IOUT = 10mA, 10Hz ≤ f ≤ 100kHz
IOUT = 10mA, 10Hz ≤ f ≤ 2.5MHz
90
800
µVRMS
µVP-P
VOUT Line Regulation VIN = 2.7V to 4.4V, IOUT = 0 l4 20 mV
VOUT Load Regulation IOUT = 1mA to 10mA
IOUT = 1mA to 30mA (Note 4)
l2
4
10 mV
mV
VOUT Shutdown Resistance CN/SHDN = 0V (Note 5)
VIN = 2.7V, Resistance Measured to Ground
VIN = 4.4V, Resistance Measured to Ground
l
l
160
100
400
300
Ω
Ω
LTC1928-5
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For more information www.linear.com/LTC 1928-5
ELECTRICAL CHARACTERISTICS
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
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: VCPO – VDROPOUT (see Figure 2).
CN/SHDN Input Threshold VIN = 2.7V to 4.4V (Note 5) l0.15 0.5 1.6 V
CN/SHDN Input Current CN/SHDN = 0V (Note 5) l–1 –3 –6 µA
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = 3V, CF LY = 0.47µF, COUT, CCPO, CIN = 4.7µF unless otherwise
specified.
TYPICAL PERFORMANCE CHARACTERISTICS
Shutdown to Enable Timing
(Figure 5)
Enable to Shutdown Timing
(Figure 5) VOUT Voltage vs Temperature
CPO Output Resistance vs VIN Min and Max VCPO vs VIN VOUT Transient Response
VIN (V)
R
CPO
(Ω)
35
30
25
20
15
10
52.5 3.0 3.5
19285 G01
4.0
4.5
TA = 25°C
CFLY = 0.47µF
IOUT = 10mA
200s/DIV
SHDN (V)V
OUT
(V)
2
0
5
4
3
2
1
0
19285 G04
TA = 25°C
VIN = 3V
VOUT = 5V
IOUT = 10mA
COUT = CCPO = 4.7µF
VIN (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)
VCPO = 1.45(VIN)
VCPO = 2(VIN)
TA = 25°C
1ms/DIV
SHDN (V)V
OUT
(V)
2
0
5
4
3
2
1
0
19285 G05
NO LOAD
TA = 25°C
VIN = 3V
VOUT = 5V
COUT = 4.7µF
TIME (µs)
0 50
∆V
OUT
(mV)I
OUT
(mA)
100 200150 250
300
19285 G03
10
5
0
–5
–10
15
10
5
0
TA = 25°C
VIN = 3V
VOUT = 5V
COUT = 4.7µF
TEMPERATURE (°C)
–50
5.030
5.020
5.010
5.000
4.990
4.980 25 75
–25 0 50 100
OUT
VIN = 3V
IOUT = 10mA
LTC1928-5
4
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For more information www.linear.com/LTC 1928-5
TYPICAL PERFORMANCE CHARACTERISTICS
Operating Current vs VIN
(No Load) Efficiency vs Supply Voltage Output Voltage vs Output Current
VIN (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
TA = 25°C
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
TA = 25°C
IOUT = 15mA
CFLY = 0.47µF
OUTPUT CURRENT (mA)
0
OUTPUT VOLTAGE (V)
35 40
19285 G09
5 10 15 20 25 30
4.901
4.900
4.989
4.988
4.987
4.986
4.985
4.984
4.983
4.982
TA = 25°C
VIN = 3V
CFLY = 0.47µF
PIN FUNCTIONS
VIN (Pin 1): Input Voltage, 2.7V to 4.4V. VIN should be
bypassed with a ≥2µF low ESR capacitor as close to the pin
as possible for best performance. A minimum capacitance
value of 0.1µF is required.
GND (Pin 2): System Ground.
VOUT (Pin 3): Low Noise Regulated Output Voltage. VOUT
should be bypassed with a ≥2µF low ESR capacitor as
close to the pin as possible for best performance. The
VOUT voltage is internally set to 5V.
CPO (Pin 4): Boosted Unregulated Voltage. Approximately
1.95VIN 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.
LTC1928-5
5
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For more information www.linear.com/LTC 1928-5
BLOCK DIAGRAM
–
+
–
+
CHARGE PUMP
AND
SLEW CONTROL
5
1
6
2
3
4
CN/SHDNCP
CLK B
ENB
CPO
V
OUT
V
IN
C
FLY
0.47µF
CCPO
4.7µF
COUT
4.7µF
POR/
SHDN
CONTROL
550kHz
OSCILLATOR
SD
BURST
VREF = 1.235V
–
+
CIN
4.7µF
SD
GND
19285 BD
160Ω
APPLICATIONS INFORMATION
Operation
The LTC1928-5 uses a switched-capacitor charge pump to
generate a CPO voltage of approximately 2VIN. CPO pow-
ers an internal low dropout linear regulator that supplies
a regulated output at VOUT. Internal comparators are used
to sense CPO and VIN voltages for power-up conditioning.
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 1.75VIN the LDO is enabled.
If CPO falls below 1.45VIN the LDO will be disabled. Gen-
erally, the charge pump runs open loop with continuous
clocking for low noise. If CPO is greater than 1.95VIN and
IOUT 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 1.95VIN 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
efficiency. The switch edge rates are also controlled to
minimize noise. The effective output resistance at CPO is
dependent on the voltage at VIN, CPO, the flying capacitor
value CF LY and the junction temperature. A low ESR capaci-
tor of ≥2µF should be used at CPO for minimum noise.
The LDO is used to filter the ripple on CPO and to set an
output voltage independent of CPO. VOUT is set by an in-
LTC1928-5
6
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For more information www.linear.com/LTC 1928-5
APPLICATIONS INFORMATION
ternal reference and resistor divider. The LDO requires a
capacitor on VOUT for stability and improved load transient
response. A low ESR capacitor of ≥2µF should be used.
Maximum IOUT 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 2VIN
(see Figure 2).
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.
COUT must be ≥2µF and CCPO must be equal to or greater
than COUT. CIN 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. CIN should be ≥2µF and a spike
reducing resistor of 2.2Ω may be required between VIN
and the supply.
A low ESR ceramic capacitor is recommended for the flying
capacitor CF LY with a value of 0.47µF. At low load or high
VIN a smaller capacitor could be used to reduce ripple on
CPO which would reflect as lower ripple on VOUT.
If a minimum enable time is required, the CPO output filter
capacitor should be at least 2× the VOUT filter capacitor.
When the LDO is first enabled, the CPO capacitor will
dump a large amount of charge into the VOUT capacitor.
If the drop in the CPO voltage falls below 1.45VIN the LDO
will be disabled and the CPO voltage will be required to
charge up to 1.75VIN 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 mini-
mize the spike component, however, low ESR capacitors
are essential to reduce the remaining spike energy effect
on the CPO voltage. CCPO should be increased for high
load currents to minimize the droop component. Ripple
components on CPO are greatly reduced at VOUT by the
LDO, however, COUT should also be a low ESR capacitor
to improve filtering of the CPO noise.
Example:
VIN = 3V
VOUT = 5V
RCPO = 30Ω
Maximum unloaded CPO voltage = 2VIN = 6V
VDROPOUT(MAX) = 100mV
IOUT(MAX) = (2VIN – VDROPOUT(MAX) – VOUT)/RCPO
= (6V – 0.1V – 5V)/30Ω = 30mA
VCPO must be greater than 1.45VIN = 4.35V. To confirm
this, calculate VCPO:
VCPO = 6V – (30mA • 30Ω) = 5.1V
For minimum noise applications the LDO must be kept out
of dropout to prevent CPO noise from coupling into VOUT.
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 VOUT. If the external
load requires 1mA, the available current at VOUT will be
reduced by 1mA.
Short-Circuit and Thermal Protection
VOUT can be shorted to ground indefinitely. Internal circuitry
will limit the output current. If the junction temperature
Figure 2. Equivalent Circuit
+–
+
–
RCPO RDROPOUT
VDROPOUT
CCPO
VCPO
VOUT
I
OUT
19285 F02
2VIN
LTC1928-5
7
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For more information www.linear.com/LTC 1928-5
APPLICATIONS INFORMATION
Shutdown
When CN/SHDN = 0V, the part will be in shutdown, the
supply current will be <8µA and VOUT will be shorted
to ground through a 160Ω switch. In addition, CPO
will be high impedance and disconnected from VIN 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.
Power-On Reset
Upon initial power-up, a power-on reset circuit ensures
that the internal functions are correctly initialized. Once VIN
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 PD = IOUT(2VIN – VOUT) + VIN(2mA). The
Figure 3. LTC1928-5 Noise Measurement Test Setup
Figure 4. LTC1928-5, External Load on CPO, No Shutdown State
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
performance 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 800µVP-P over a 2.5MHz bandwidth. The noise
measurement involves AC-coupling the LTC1928 output
into the test setup’s input and terminating this connec-
tion with 50Ω. Coaxial connections must be maintained
to preserve measurement integrity.
LTC1928
DEMO
BOARD OSCILLOSCOPE
BANDWIDTH
FILTER
CONNECT BNC AND
RLOAD 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
VOUT
RLOAD 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×
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
V
IN
3V
CCPO
4.7µF
10µF
19285 F04
LTC1928-5
ADDITIONAL
LDO
VRIPPLE < 800µVP-P
LTC1928-5
8
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For more information www.linear.com/LTC 1928-5
PACKAGE DESCRIPTION
Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.
1.50 – 1.75
(NOTE 4)
2.80 BSC
0.30 – 0.45
6 PLCS (NOTE 3)
DATUM ‘A’
0.09 – 0.20
(NOTE 3) S6 TSOT-23 0302
2.90 BSC
(NOTE 4)
0.95 BSC
1.90 BSC
0.80 – 0.90
1.00 MAX 0.01 – 0.10
0.20 BSC
0.30 – 0.50 REF
PIN ONE ID
NOTE:
1. DIMENSIONS ARE IN MILLIMETERS
2. DRAWING NOT TO SCALE
3. DIMENSIONS ARE INCLUSIVE OF PLATING
4. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR
5. MOLD FLASH SHALL NOT EXCEED 0.254mm
6. JEDEC PACKAGE REFERENCE IS MO-193
3.85 MA
X
0.62
MAX
0.95
REF
RECOMMENDED SOLDER PAD LAYOUT
PER IPC CALCULATOR
1.4 MIN
2.62 REF
1.22 REF
S6 Package
6-Lead Plastic TSOT-23
(Reference LTC DWG # 05-08-1636)
LTC1928-5
9
19285fa
For more information www.linear.com/LTC 1928-5
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 representa-
tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.
REVISION HISTORY
REV DATE DESCRIPTION PAGE NUMBER
A 09/15 Revised package drawing. 8
LTC1928-5
10
19285fa
For more information www.linear.com/LTC 1928-5
LINEAR TECHNOLOGY CORPORATION 2000
LT 0915 REV A • PRINTED IN USA
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com/LTC1928-5
RELATED PARTS
TYPICAL APPLICATION
3
4
2
1
5
6
VIN
CP
CN/SHDN
VOUT
CPO
GND
100Ω
2N7002 SHDN
COUT
4.7µF
CIN
4.7µF CFLY
0.47µF
5V
VIN
2.7V TO 4.4V
CCPO
4.7µF
19285 F05
LTC1928-5
VRIPPLE < 800µVP-P
PART NUMBER DESCRIPTION COMMENTS
LTC1550/LTC1551 Low Noise, 900kHz Charge Pump 1mVP-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 60µVRMS Noise, IOUT Up to 80mA, MSOP
LTC1754-5 Micropower 5V Charge Pump in ThinSOT IQ = 13µA, IOUT to 50mA, Shutdown
LT1761 Series 100mA ThinSOT, Low Noise LDO Regulators 20µA IQ, 20µVRMS Noise, 300mV Dropout
LTC3200 Constant Frequency Doubler Charge Pump Low Noise, 5V Output or Adjustable
Figure 5. Low Noise 5V Supply with Shutdown