5

LTC1429

pump to operate erratically or the device to shut down. A

logic high or low at the SYNC/SD pin will put the device

into SHUTDOWN and drop the supply current to 0.2

µA.

The LTC1429 will operate with input square wave of 40%

to 60% duty cycle. For best performance, use a square

wave of 50% duty cycle.

voltage between 3V and 6.5V. Certain combinations of

output voltage and operating mode may place additional

restrictions on the input voltage; see the Applications

ground with at least a 0.1

µF capacitor, placed in close

proximity to the chip; again, see the Applications Informa-

tion section.

TEST CIRCUITS

Figure 2. Tripler Mode

effect on output ripple; see the Applications Information

section for more details.

REG (Pin 12/Pin 7): This is an open drain output that pulls

low when the output voltage is within 5% of the set value.

It will sink 10mA to ground with a 5V supply. The external

circuitry must provide a pull-up or REG will not swing high.

12V above ground without damage.

SYNC/SD (Pin 13/Pin 8): Synchronous Clock Input. A

keep the LTC1429 operating normally. An input clock

below the minimum frequency may cause the charge

Figure 1. Doubler Mode

1

2

3

4

8

7

6

5

0.1

µF

10

µF

0.001

µF

5V

3.3

µF

GND

SYNC/SD

COMP

REG

OUT

LTC1429-4CS8

LTC1429 • TC01

MODES OF OPERATION

The LTC1429 uses a charge pump to generate a negative

output voltage that can be regulated to a value either

higher or lower than the original input voltage. It has two

modes of operation: a doubler inverting mode, which can

provide a negative output equal to or less than the positive

power supply, and a tripler inverting mode, which can

provide negative output voltages either larger or smaller in

magnitude than the original positive supply. The tripler

offers greater versatility and wider input range but re-

quires four external capacitors and a 14-pin package; the

doubler offers the SO-8 package and requires only three

external capacitors. The optional compensation capacitor

at ADJ/COMP is used to reduce the ripple output voltage.

Doubler Mode

This mode allows the LTC1429 to generate negative

output voltage magnitudes up to that of the supply voltage,

10

9

8

13

7

11

0.001

µF

3.3

µF

LTC1429 • TC02

NC

NC

10

µF

+

GND

ADJ

SYNC/SD

R0

OUT

R1

LTC1429CS

14

6

2

3

4

5

0.1

µF

0.1

µF