LTC1261CS datasheet(5/16 Pages) LINER

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LTC1261

PIN FUNCTIONS

Pin numbers are shown as (LTC1261CS/LTC1261CS8).

NC (Pin 1/NA): No Internal Connection.

C1+ (Pin 2/ Pin 2): C1 Positive Input. Connect a 0.1

µF

capacitor between C1+ and C1–. With the LTC1261CS in

doubler mode, connect a 0.1

µF capacitor from C1+ to

C2 –.

C1– (Pin 3/Pin 3): C1 Negative Input. Connect a 0.1

µF

capacitor from C1+ to C1–. With the LTC1261CS in

doubler mode only, C1– should float.

C2 + (Pin 4/NA): C2 Positive Input. In tripler mode con-

nect a 0.1

µF capacitor from C2+ to C2–. This pin is used

with the LTC1261CS in tripler mode only; in doubler

mode this pin should float.

C2 – (Pin 5/NA): C2 Negative Input. In tripler mode

connect a 0.1

µF capacitor from C2+ to C2 –. In doubler

mode connect a 0.1

µF capacitor from C1+ to C2–.

GND (Pin 6/Pin 4): Ground. Connect to a low impedance

ground. A ground plane will help to minimize regulation

errors.

R0 (Pin 7/NA): Internal Resistor String, 1st Tap. See

Table 2 in the Applications Information section for infor-

mation on internal resistor string pin connections vs

output voltage.

R1 (Pin 8/NA): Internal Resistor String, 2nd Tap.

RADJ (Pin 9/NA): Internal Resistor String Output. Con-

nect this pin to ADJ to use the internal resistor divider.

See Table 2 in the Applications Information section for

information on internal resistor string pin connections vs

output voltage.

ADJ (COMP for fixed versions) (Pin 10/Pin 5): Output

Adjust/Compensation Pin. For adjustable parts this pin is

used to set the output voltage. The output voltage should

be divided down with a resistor divider and fed back to

this pin to set the regulated output voltage. The resistor

divider can be external or the internal divider string can

be used if it can provide the required output voltage.

Typically the resistor string should draw

≥10µA from the

output to minimize errors due to the bias current at the

adjust pin. Fixed output parts have the internal resistor

string connected to this pin inside the package. The pin

can be used to trim the output voltage if desired. It can

also be used as an optional feedback compensation pin

to reduce output ripple on both adjustable and fixed

output voltage parts. See Applications Information sec-

tion for more information on compensation and output

ripple.

OUT (Pin 11/Pin 6): Negative Voltage Output. This pin

must be bypassed to ground with a 1

µF or larger capaci-

tor; it must be at least 3.3

µF to provide specified output

ripple. The size of the output capacitor has a strong effect

on output ripple. See the Applications Information sec-

tion 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 8mA to ground with a 5V supply. The external

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

high. The voltage at REG may exceed VCC and can be

pulled up to 12V above ground without damage.

SHDN (Pin 13/Pin 8): Shutdown. When this pin is at

ground the LTC1261 operates normally. An internal 5

µA

pull-down keeps SHDN low if it is left floating. When

SHDN is pulled high, the LTC1261 enters shutdown

mode. In shutdown the charge pump stops, the output

collapses to 0V and the quiescent current drops to 5

µA

typically.

VCC (Pin 14/Pin 1): Power Supply. This requires an input

voltage between 3V and 6.5V. Certain combinations of

output voltage and operating mode may place additional

restrictions on the input voltage. VCC must be bypassed

to ground with at least a 0.1

µF capacitor placed in close

proximity to the chip. See the Applications Information

section for details.

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