LTC3265 datasheet(13/20 Pages) LINER

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LTC3265

3265fa

For more information www.linear.com/LTC3265

OPERATION

Negative Low Dropout Linear Regulator (LDO–)

The negative low dropout regulator (LDO–) supports a

load of up to 50mA. The LDO– takes power from the VOUT–

pin (output of the inverting charge pump) and drives the

LDO– output pin to a voltage programmed by the resistor

divider connected between LDO–, ADJ– and GND pins. For

stability,theLDO–outputmustbebypassedtogroundwith

a low ESR ceramic capacitor that maintains a capacitance

of at least 2µF across operating temperature and voltage.

The LDO– is enabled or disabled via the EN– logic input

pin. Initially, when the EN– logic input is low, the charge

pump circuitry is disabled and the VOUT– pin is at GND.

When EN– is switched high, the VOUT– pin will be driven

1.2V REF

BYP+

GND

CBYP+

COUT

COPT

LDO

OUTPUT

3265 F02

ADJ+

LDO+

EN+

VOUT+

Figure 2. Positive LDO Application Circuit

Figure 3: Negative LDO Application Circuit

–1.2V REF

BYP–

GND

CBYP–

COUT

LDO

OUTPUT

3265 F03

ADJ–

LDO–

EN–

VOUT–

COPT

negative by the charge pump circuitry. Soft-start circuitry

in the charge pump also provides soft-start functionality

for the LDO– and prevents excessive inrush currents.

Figure 3 shows the LDO– regulator application circuit.

The LDO– output voltage VLDO– can be programmed by

choosing suitable values of R1 and R2 such that:

VLDO– = –1.2V •









An optional capacitor of 100nF can be connected from the

BYP– pin to ground. This capacitor bypasses the internal

–1.2V reference of the LTC3265 and improves the noise

performance of the LDO–. If this function is not used the

BYP– pin should be left floating.

An optional feedback capacitor (COPT) can be added for

improved transient response. A value of 10pF is recom-

mended for most applications but experimentation with

capacitor sizes between 2pF and 22pF may yield further

improvement in the transient response.

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