LTC1429CS8-4 datasheet(6/12 Pages) LINER

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LTC1429

APPLICATIONS INFORMATION

creating a voltage between VCC and OUT of up to 2 × VCC.

In doubler mode, the LTC1429 uses a single flying capaci-

tor to invert the input supply voltage and the output voltage

is stored on the output bypass capacitor between switch

cycles. The LTC1429CS8 is always configured in doubler

mode and has only one pair of flying capacitor pins (Figure

3a). The LTC1429CS can be configured in doubler mode by

connecting a single flying capacitor between the C1+ and

C2– pins; C1– and C2+ should be left floating (Figure 3b).

voltage; the total voltage between the VCC and OUT pins is

× VCC. Tripler mode can be used to generate –5V from

a single positive 3.3V supply, for example. Tripler mode

requires two external flying capacitors. The first connects

between C1+ and C1– and the second between C2+ and C2–

(Figure 3c). Because of the relatively high voltages that can

be generated in this mode, care must be taken to ensure

that the total input-to-output voltage never exceeds 12V,

or the LTC1429 may be damaged. This is possible with

supply voltages above 4V in tripler mode and above 6V in

doubler mode, although in most applications the output

voltage will be kept in check by the regulation loop. As the

input supply voltage rises, the allowable output voltage

drops, finally reaching – 4V with a 8.5V supply. To avoid

this problem, use doubler mode whenever possible with

high input supply voltages.

THEORY OF OPERATION

A block diagram of the LTC1429 is shown in Figure 4. The

heart of the LTC1429 is the charge pump core, shown in the

dashed line. It generates a negative output voltage by first

charging the flying caps between VCC and ground. It then

Figure 4. Block Diagram

C1+

C1–

C2+

LTC1429CS

LTC1429 • F03

C2–

C1+

C1–

C2+

LTC1429CS

C2–

C1+

C1–

LTC1429CS8

(a)

SO-8 DOUBLER MODE

(b)

S0-14 DOUBLER MODE

(c)

SO-14 TRIPLER MODE

Figure 3. Flying Capacitor Connections

Tripler Mode

The LTC1429CS can be used in a tripler mode which can

generate negative output voltages up to twice the supply

VCC

VOUT

LTC1429 • F04

60mV

1.18V

1.24V

RADJ*

R1*

R0*

*LTC1429CS14 ONLY

COUT

C1–

C1+

C2–

50k

100k

226k

INTERNALLY

CONNECTED FOR

FIXED OUTPUT

VOLTAGE PARTS

124k

C2+

ADJ/COMP

REG

SHUTDOWN

–

COMP 1

–

COMP 2

SYNC/SD

DELAY

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