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LTC1261C

Switched Capacitor Regulated Voltage Inverter

Linear Technology 

LTC1261

PIN FUNCTIONS (CS/CS8)

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

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

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

doubler mode, connect a 0.1µF capacitor from C1+ to C2–.

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

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 connect

a 0.1µF 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 con-

nect a 0.1µF capacitor from C2+ to C2–. In doubler mode

connect a 0.1µF 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 information 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. Connect

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 con-

nected 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 section 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 1µF or larger capaci-

tor; it must be at least 3.3µF to provide specified output

ripple. The size of the output capacitor has a strong 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 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 5µA 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 5µA 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 0.1µF capacitor placed in close

proximity to the chip. See the Applications Information

section for details.

For more information www.linear.com/LTC1261

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