DEMO MANUAL DC239
NO-DESIGN SWITCHER
LTC1502-3.3
Single Cell to 3.3V Regulated
Charge Pump DC/DC Converter
DESCRIPTIO
U
power conscious single-cell applications. The maximum
output load is 10mA for input voltages greater than or
equal to 1V. A jumper is available to put the circuit into
shutdown mode, which reduces input quiescent current to
5µA (typ) and disconnects V
OUT
from V
IN
.
Gerber files for
this circuit are available. Call the LTC factory.
, LTC and LT are registered trademarks of Linear Technology Corporation.
I
OUT
= 1mA
3.3
I
OUT
= 10mA
I
OUT
= 15mA
1.4
1.6
1.2
INPUT VOLTAGE (V)
1.8
1502-3.3 TA02
Demonstration Circuit DC239 is a quadrupler charge pump
DC/DC converter that produces a regulated 3.3V output
from a single alkaline cell input. The circuit requires only
five small external capacitors and no inductors. Low
supply current (40µA typ) and minimal external compo-
nent area make this power supply ideal for space and
PERFOR A CE SU
PARAMETER
V
IN
Operating Voltage
Minimum V
IN
Start-Up Voltage
V
OUT
V
IN
Operating Current
V
IN
Shutdown Current
Output Ripple
Efficiency
TYPICAL PERFOR A CE CHARACTERISTICS A D BOARD PHOTO
Output Voltage vs Input Voltage
3.5
T
A
= 25°C
3.4
OUTPUT VOLTAGE (V)
3.2
3.1
3.0
0.8
1.0
U
WW
U W
U W
ARY
Operating Temperature Range 0°C to 70°C
MIN
0.9
TYP
0.75
3.17
3.3
40
5
50
77
MAX
1.8
0.9
3.43
90
15
UNITS
V
V
V
µA
µA
mV
P-P
%
CONDITIONS
100kΩ V
OUT
Load
I
OUT
≤
10mA, 1V
≤
V
IN
≤
1.8V
I
OUT
= 0mA, 0.9V
≤
V
IN
≤
1.8V
C1
–
/SHDN = 0V, 0.9V
≤
V
IN
≤
1.8V
I
OUT
= 10mA, V
IN
= 1.25V
V
IN
= 1V, I
OUT
= 10mA
Component Side
1
DEMO MANUAL DC239
NO-DESIGN SWITCHER
SCHE ATIC A D PACKAGE DIAGRA S
Demo Board Schematic
U1
1
C2
10µF
2
C2
V
OUT
8
J2
V
OUT
C
OUT
3.3V/10mA
10µF
J1
J3
V
IN
J4
DC239 SCHEM
R1
100Ω
JP1
ON
SHDN
7
C3
+
C1
+
C1
LTC1502-3.3
1µF 3
6
C1
–
/SHDN C3
–
4
5
GND
V
IN
C3
1µF
C
IN
10µF
PARTS LIST
REFERENCE
DESIGNATOR
C1, C3
C2, C
OUT
, C
IN
JP1
J1, J2, J3, J4
R1
U1
QUANTITY
2
3
1
4
1
1
1
PART NUMBER
0603ZG105ZAT1A
1206ZG106ZAT1A
2802S-03G2
2501-2
CR16-101JM
LTC1502CMS8-3.3
CCIJ2mm-138-G
DESCRIPTION
1µF 10V Y5V Capacitor
10µF 10V Y5V Capacitor
3-Pin, 2mm Jumper
0.090 Turret Testpoint
100Ω 1/16W 5% Chip Resistor
MSOP Step-Up DC/DC IC
2-Pin 2mm Shunt
VENDOR
AVX
AVX
Comm Con
Mill-Max
TAD
LTC
Comm Con
TELEPHONE
(843) 946-0362
(843) 946-0362
(626) 301-4200
(516) 922-6000
(800) 508-1521
(408) 432-1900
(626) 301-4200
OPERATIO
The LTC1502-3.3 uses a switched capacitor quadrupler
charge pump to produce a boosted output voltage. The
quadrupler charge pump consists of two voltage doubler
charge pumps (CP1 and CP2 on the Block Diagram)
cascaded in series. CP1 doubles the input voltage V
IN
, and
the CP1 output voltage is stored on external capacitor C2.
The C2 pin also serves as the input for doubler CP2, whose
output is stored on the output capacitor C
OUT
. Each
doubler is controlled by a 2-phase clock that is generated
in the timing-control circuit. On phase one of the clock, the
flying capacitors C1 and C3 are charged to their respective
input voltages. On phase two, each charged flying capaci-
tor is stacked on top of the input voltage and discharged
through an internal switch onto its respective output. This
sequence of charging and discharging the flying capaci-
tors (CP1 and CP2) continues at the free running oscillator
frequency (500kHz typ) until the output is in regulation.
Regulation is achieved by comparing the divided output
voltage to a fixed voltage reference. The charge pump
2
W
U
U
W
TOP VIEW
C2
C1
+
C1
–
/SHDN
GND
1
2
3
4
8
7
6
5
V
OUT
C3
+
C3
–
V
IN
MS8 PACKAGE
8-LEAD PLASTIC MSOP
LTC1502CMS8-3.3
clocks are disabled when the output voltage is above the
desired regulation point set by COMP1. When the output
has dropped below the lower trip point of COMP1, the
charge pump clocks are turned back on until V
OUT
is
boosted back into regulation.
Enhanced Start-Up
Enhanced start-up capability is provided by the COMP2
circuitry. COMP2 compares the divided C2 voltage to the
input voltage, V
IN
. The COMP2 output disables the output
charge pump, CP2, whenever the divided C2 voltage is
lower than V
IN
. The CP2 output is thereby forced into a
high impedance state until the voltage on C2 has been
raised above V
IN
(the C2 pin should not be loaded for
proper start-up). This allows a higher internal gate drive
voltage to be generated (from the C2 pin) before the part’s
output (V
OUT
) is connected to a load. Hysteresis in COMP2
forces CP2 to be turned ON and OFF while C
OUT
is charged
DEMO MANUAL DC239
NO-DESIGN SWITCHER
OPERATIO
V
IN
5
C
IN
2.5µA
CP1
400k
V
IN
CP2
8
V
OUT
C
OUT
COMP3
U2
0.55V
HIZ1
CLK1/CLK2
1M
SHDN
TIMING
CONTROL
OSCEN
U3
C2
V
OUT
BIAS
CONTROL
INTERNAL
V
CC
COMP1
to prevent a lock-up condition if C2 droops too low during
start-up. By the time the output nears the regulation point,
the C2 voltage is well above the lower trip point of COMP2
and CP2 will remain enabled. This method of disabling the
output charge pump while an internal boosted gate drive
supply is developed allows the part to start up at low
voltages with a larger output current load than would
otherwise be possible.
Shutdown
Shutdown is implemented using an external pull-down
device on the C1
–
/SHDN pin. The demo circuit provides a
jumper that selects either the ON or SHDN state. In the ON
state, the 100Ω external pull-down resistor is left floating.
In the SHDN state, the resistor is shorted to ground
through the jumper. The center pin of the jumper can be
driven with an external, open-drain device to test the AC
start-up and shutdown characteristics. The shutdown
feature can be used to prevent charge pump switching
during noise sensitive intervals. The LTC1502-3.3 takes
between 20µs and 50µs to switch from shutdown to active
mode once the pull-down device has been turned off.
During shutdown, V
OUT
is disconnected from V
IN
.
Short-Circuit Protection
When the output pin is shorted to ground, the LTC1502-
3.3 will continuously charge the C2 capacitor to approxi-
mately 1.4 times V
IN
and then discharge C2 into the
shorted output. Since the discharging of C2 into V
OUT
will
bring the C2 voltage below the COMP2 start-up trip
voltage, the output charge pump will be forced Hi-Z while
C2 charges again. Hence, the internal charge pump gate
drive voltage is limited to 1.4 • V
IN(MAX)
(on the C2 pin),
and no continuous current is supplied to V
OUT
. The result-
ing output short-circuit current is limited to under 30mA
(typ), thereby allowing the LTC1502-3.3 to endure an
indefinite output short circuit without damage. When the
short is removed, the part will start up and operate
normally.
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.
–
+
+
+
–
–
+
U
LTC1502-3.3 Block Diagram
C1
C2
C3
SHUTDOWN
C1
–
/SHDN
C1
+
C2
C3
–
C3
+
3
2
1
6
7
HIZ2
2.1M
COMP2
U4
1.2M
1.2V
REF
4
GND
1502-3.3 BD
3
DEMO MANUAL DC239
NO-DESIGN SWITCHER
PCB LAYOUT A D FIL
Component Side Silkscreen
Component Side Paste Mask
PC FAB DRAWI G
2.00
NOTES: UNLESS OTHERWISE SPECIFIED
1. ALL DIMENSIONS ARE IN INCHES
2. FINISHED MATERIAL IS FR4, 0.062 THICK
2 OZ COPPER, 2 LAYERS. PLATED HOLE
WALL THICKNESS 0.001 MIN
3. PROCESS: SMOBC
NUMBER
OF HOLES PLTD
3
4
7
PLTD
PLTD
A
4
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408)432-1900
q
FAX: (408) 434-0507
q
www.linear-tech.com
W
Copper Layer 1 (Top)
Component Side Solder Mask
Copper Layer 2
Solder Side Solder Mask
B
2.00
SYMBOL
A
B
B
DIAMETER
0.030
0.094
TOTAL HOLES
DC239 FAB DWG
U
U
dc239f LT/TP 0799 500 • PRINTED IN USA
©
LINEAR TECHNOLOGY CORPORATION 1999
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