Linear Technology DC239 Demo Manual

DESCRIPTIO

DEMO MANUAL DC239

NO-DESIGN SWITCHER

LTC1502-3.3

Single Cell to 3.3V Regulated

Charge Pump DC/DC Converter

U

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

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

from VIN. Gerber files for

OUT

this circuit are available. Call the LTC factory.

, LTC and LT are registered trademarks of Linear Technology Corporation.

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PERFOR A CE SU ARY

PARAMETER CONDITIONS MIN TYP MAX UNITS

VIN Operating Voltage 0.9 1.8 V

Minimum V

V

OUT

VIN Operating Current I

VIN Shutdown Current C1

Output Ripple I

Efficiency VIN = 1V, I

Start-Up Voltage 100kΩ V

IN

Operating Temperature Range 0°C to 70°C

Load 0.75 0.9 V

OUT

I

≤ 10mA, 1V ≤ VIN ≤ 1.8V 3.17 3.3 3.43 V

OUT

= 0mA, 0.9V ≤ VIN ≤ 1.8V 40 90 µA

OUT

–

/SHDN = 0V, 0.9V ≤ VIN ≤ 1.8V 5 15 µA

= 10mA, VIN = 1.25V 50 mV

OUT

= 10mA 77 %

OUT

P-P

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TYPICAL PERFOR A CE CHARACTERISTICS A D BOARD PHOTO

Output Voltage vs Input Voltage

3.5
T

= 25°C

A

3.4

I

= 1mA

3.3

3.2

OUTPUT VOLTAGE (V)

3.1

3.0

0.8

OUT

I

= 10mA

OUT

= 15mA

I

OUT

1.0

1.2

INPUT VOLTAGE (V)

1.4

1.6

1502-3.3 TA02

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Component Side

1.8

1

DEMO MANUAL DC239

1
2
3
4

C2

C1

+

C1–/SHDN

GND

8
7
6
5

V

OUT

C3

+

C3

–

V

IN

TOP VIEW

MS8 PACKAGE

8-LEAD PLASTIC MSOP

NO-DESIGN SWITCHER

W

U

W

SCHE ATIC A D PACKAGE DIAGRA S

Demo Board Schematic

ON

C2
10µF

R1
100Ω

JP1

SHDN

C1
1µF

1

C2

2

C1

LTC1502-3.3

3

C1–/SHDN

4

GND

U1

8

V

OUT

+

7

+

C3

–

C3

V

IN

C3
1µF

6

5

C

IN

10µF

C

OUT

10µF

DC239 SCHEM

J2
V

OUT

3.3V/10mA

J1

J3
V

IN

J4

LTC1502CMS8-3.3

PARTS LIST

REFERENCE
DESIGNATOR QUANTITY PART NUMBER DESCRIPTION VENDOR TELEPHONE

C1, C3 2 0603ZG105ZAT1A 1µF 10V Y5V Capacitor AVX [phone]

C2, C
JP1 1 2802S-03G2 3-Pin, 2mm Jumper Comm Con [phone]
J1, J2, J3, J4 4 2501-2 0.090 Turret Testpoint Mill-Max [phone]

R1 1 CR16-101JM 100Ω 1/16W 5% Chip Resistor TAD [phone]

U1 1 LTC1502CMS8-3.3 MSOP Step-Up DC/DC IC LTC [phone]

OUT

, C

IN

3 1206ZG106ZAT1A 10µF 10V Y5V Capacitor AVX [phone]

1 CCIJ2mm-138-G 2-Pin 2mm Shunt Comm Con [phone]

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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 VIN, 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
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 capaci­tor 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 capaci­tors (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

OUT

. Each

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, VIN. The COMP2 output disables the output
charge pump, CP2, whenever the divided C2 voltage is
lower than VIN. The CP2 output is thereby forced into a
high impedance state until the voltage on C2 has been
raised above VIN (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
forces CP2 to be turned ON and OFF while C

) is connected to a load. Hysteresis in COMP2

OUT

is charged

OUT

OPERATIO

DEMO MANUAL DC239

NO-DESIGN SWITCHER

U

LTC1502-3.3 Block Diagram

C2

SHUTDOWN

–

/SHDN

C1

V

IN

5

C

IN

U2

2.5µA

–

+

+

0.55V

SHDN OSCEN

HIZ1

CLK1/CLK2

TIMING

CONTROL

32

CP1

+

C1

400k

V

IN

C2

1 6 7

–

+

1M

U3

COMP2COMP3

U4

C3

HIZ2

C3C1

–

CP2

+

C3

8

2.1M

V

OUT

C

OUT

–

1.2M

+

C2

V

OUT

BIAS

CONTROL

INTERNAL
V

CC

COMP1

1.2V
REF

4

GND

1502-3.3 BD

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

is disconnected from VIN.

OUT

Short-Circuit Protection

When the output pin is shorted to ground, the LTC1502-

3.3 will continuously charge the C2 capacitor to approxi­mately 1.4 times VIN 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)

and no continuous current is supplied to V

(on the C2 pin),

. The result-

OUT

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 represen­tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.

3

DEMO MANUAL DC239

NO-DESIGN SWITCHER

W

PCB LAYOUT AUD FIL

Component Side Silkscreen Component Side Solder Mask

Component Side Paste Mask

Copper Layer 1 (Top)

Copper Layer 2

Solder Side Solder Mask

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PC FAB DRAWI

G

A

Linear Technology Corporation

4

1630 McCarthy Blvd., Milpitas, CA 95035-7417

[phone] ● FAX: [phone]

●

www.linear-tech.com

2.00

B

B

DC239 FAB DWG

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

2.00

SYMBOL

A

B

DIAMETER

0.030

0.094

TOTAL HOLES

NUMBER

OF HOLES

PLTD

3

PLTD

4

PLTD

7

dc239f LT/TP 0799 500 • PRINTED IN USA

 LINEAR TECHNOLOGY CORPORATION 1999