LTC1928-5
Doubler Charge Pump with
Low Noise Linear Regulator
in ThinSOT
FEATURES
s
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DESCRIPTIO
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.
, LTC and LT are registered trademarks of Linear Technology Corporation
ThinSOT is a trademark of Linear Technology Corporation.
APPLICATIO S
s
s
s
s
s
s
s
s
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
TYPICAL APPLICATION
LTC1928-5
V
IN
2.7V TO 4.4V
4.7µF
0.47µF
1
5
6
V
IN
CP
V
OUT
CPO
3
4
2
4.7µF
19285 F01
Output Noise (BW = 10Hz to 2.5MHz)
5V
V
OUT
4.7µF
V
OUT
200µV/DIV
CN/SHDN GND
Figure 1. Low Noise 5V Power Supply
C
CPO
= C
OUT
= 4.7µF 100µs/DIV
I
OUT
= 10mA
V
IN
= 3V
V
OUT
= 5V
T
A
= 25°C
U
19285 TA01
U
U
1
LTC1928-5
ABSOLUTE
(Note 1)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
V
IN
1
GND 2
V
OUT
3
6 CN/SHDN
5 CP
4 CPO
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
ORDER PART
NUMBER
LTC1928ES6-5
S6 PART MARKING
LTKT
S6 PACKAGE
6-LEAD PLASTIC SOT-23
T
JMAX
= 125°C,
θ
JA
= 230°C/ W
Consult factory for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
The
q
denotes specifications which apply over the full operating temperature range, otherwise specifications are T
A
= 25°C.
V
IN
= 3V, C
FLY
= 0.47µF, C
OUT
, C
CPO
, C
IN
= 4.7µF unless otherwise specified.
PARAMETER
V
IN
Operating Voltage
I
VIN
Shutdown Current
I
VIN
Operating Current
Regulated Output Voltage
V
OUT
Temperature Coefficient
Charge Pump Oscillator Frequency
CPO Output Resistance
V
OUT
Dropout Voltage (Note 3)
V
OUT
Enable Time
V
OUT
Output Noise Voltage
V
OUT
Line Regulation
V
OUT
Load Regulation
V
OUT
Shutdown Resistance
I
OUT
> 500µA, V
IN
= 2.7V to 4.4V
V
IN
= 2.7V, I
OUT
= 10mA
V
IN
= 4.4V, I
OUT
= 10mA
I
OUT
= 10mA, V
OUT
= 5V
R
LOAD
= 2k
I
OUT
= 10mA, 10Hz
≤
f
≤
100kHz
I
OUT
= 10mA, 10Hz
≤
f
≤
2.5MHz
V
IN
= 2.7V to 4.4V, I
OUT
= 0
I
OUT
= 1mA to 10mA
I
OUT
= 1mA to 30mA (Note 4)
CN/SHDN = 0V (Note 5)
V
IN
= 2.7V, Resistance Measured to Ground
V
IN
= 4.4V, Resistance Measured to Ground
V
IN
= 2.7V to 4.4V (Note 5)
CN/SHDN = 0V (Note 5)
q
q
q
q
q
q
CONDITIONS
q
MIN
2.7
q
q
q
TYP
4
190
MAX
4.4
8
330
5.1
620
30
24
100
UNITS
V
µA
µA
V
ppm
kHz
Ω
Ω
mV
ms
µV
RMS
µV
P-P
SHDN = 0V (Note 5)
I
OUT
= 0mA, Burst Mode
TM
Operation
I
OUT
= 1mA
4.9
480
5
±50
550
17
14
0.6
90
800
4
2
4
160
100
20
10
q
q
q
q
400
300
1.6
–6
CN/SHDN Input Threshold
CN/SHDN Input Current
0.15
–1
0.5
–3
Burst Mode is a trademark of Linear Technology Corporation.
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).
2
U
mV
mV
mV
Ω
Ω
V
µA
W
U
U
W W
W
LTC1928-5
ELECTRICAL CHARACTERISTICS
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.
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.
TYPICAL PERFOR A CE CHARACTERISTICS
CPO Output Resistance vs V
IN
35
T
A
= 25°C
C
FLY
= 0.47µF
30 I
OUT
= 10mA
25
R
CPO
(Ω)
V
CPO
(V)
8
V
CPO
= 2(V
IN
)
7
6
5
(A)
(B)
V
CPO
= 1.45(V
IN
)
∆V
OUT
(mV)
20
15
I
OUT
(mA)
10
3
5
2.5
3.0
3.5
V
IN
(V)
4.0
4.5
19285 G01
Shutdown to Enable Timing
(Figure 5)
SHDN (V)
SHDN (V)
2
0
5
4
2
0
V
OUT
VOLTAGE (V)
V
OUT
(V)
3
2
1
0
T
A
= 25°C
V
IN
= 3V
V
OUT
= 5V
I
OUT
= 10mA
C
OUT
= C
CPO
= 4.7µF
200µs/DIV
19285 G04
V
OUT
(V)
U W
Min and Max V
CPO
vs V
IN
9
T
A
= 25°C
10
5
0
–5
–10
15
10
5
0
V
OUT
Transient Response
T
A
= 25°C
V
IN
= 3V
V
OUT
= 5V
C
OUT
= 4.7µF
4
2.5
3.0
3.5
V
IN
(V)
4.0
4.5
0
50
100
150
200
TIME (µs)
250
300
(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
19285 G02
19285 G03
Enable to Shutdown Timing
(Figure 5)
5.040
5.030
5.020
5.010
5.000
4.990
V
OUT
Voltage vs Temperature
V
IN
= 3V
I
OUT
= 10mA
5
4
3
2
1
0
NO LOAD
T
A
= 25°C
V
IN
= 3V
V
OUT
= 5V
C
OUT
= 4.7µF
1ms/DIV
19285 G05
4.980
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
19285 G06
3
LTC1928-5
TYPICAL PERFOR A CE CHARACTERISTICS
Operating Current vs V
IN
(No Load)
260
240
T
A
= 25°C
100
90
80
70
60
50
OPERATING CURRENT (µA)
OUTPUT VOLTAGE (V)
220
200
180
160
140
120
100
2.5
3.0
3.5
V
IN
(V)
4.0
4.5
19285 G07
EFFICIENCY (%)
BLOCK DIAGRA
V
IN
C
IN
4.7µF
1
CLK B
ENB
POR/
SHDN
CONTROL
+
550kHz
OSCILLATOR
BURST
SD
+
–
3
V
REF
= 1.235V
160Ω
SD
V
OUT
C
OUT
4.7µF
4
–
+
U W
CP
Efficiency vs Supply Voltage
T
A
= 25°C
I
OUT
= 15mA
C
FLY
= 0.47µF
Output Voltage vs Output Current
4.901
4.900
4.989
4.988
4.987
4.986
4.985
4.984
4.983
T
A
= 25°C
V
IN
= 3V
C
FLY
= 0.47µF
40
2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4
SUPPLY VOLTAGE (V)
19285 G08
4.982
0
5
10 15 20 25 30
OUTPUT CURRENT (mA)
35
40
19285 G09
W
C
FLY
0.47µF
5
6
CN/SHDN
CHARGE PUMP
AND
SLEW CONTROL
4
CPO
C
CPO
4.7µF
–
2
GND
19285 BD
LTC1928-5
PIN FUNCTIONS
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.
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.
APPLICATIONS INFORMATION
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.
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
.
U
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