LT1054

SWITCHEDCAPACITOR VOLTAGE CONVERTERS

WITH REGULATORS

SLVS033F − FEBRUARY 1990 − REVISED NOVEMBER 2004

11

POST OFFICE BOX 655303

APPLICATION INFORMATION

regulation

The feedback/shutdown (FB/SD) terminal has two functions. Pulling FB/SD below the shutdown threshold

(

≈ 0.45 V) puts the device into shutdown. In shutdown, the reference/regulator is turned off and switching stops.

in shutdown drops to approximately 100

µA. Any open-collector gate can be used to put the LT1054 into

shutdown. For normal (unregulated) operation, the device will restart when the external gate is shut off. In

LT1054 circuits that use the regulation feature, the external resistor divider can provide enough pulldown to keep

LT1054 is run intermittently, this does not present a problem because the discharge time of the output capacitor

is short compared to the off time of the device. In applications where the device has to start up before the output

signal into FB/SD allows the output voltage to rise and regulate without overshoot. The resistor divider R3/R4

shown in Figure 16 should be chosen to provide a signal level at FB/SD of 0.7−1.1 V.

FB/SD also is the inverting input of the LT1054 error amplifier and, as such, can be used to obtain a regulated

output voltage.

VIN

R2

R1

R4

R3

Restart

Shutdown

C1

5

6

7

8

+

CIN

10-

µF

Tantalum

4

3

2

1

LT1054

VOUT

VREF

OSC

VCC

CAP−

GND

CAP+

FB/SD

VOUT

Where: R1 = 20 k

Ω

VREF = 2.5 V Nominal

+

2.2

µF

For example: To get VO = −5 V, referenced to the ground terminal of the LT1054

† Choose the closest 1% value.

Pin numbers shown are for the P package.

COUT

100-

µF

Tantalum

R2

+ R1

V

OUT

V

REF

2

* 40 mV

) 1

+ 20 kW

|–5 V|

2.5 V

2

* 40 mV

) 1

+ 102.6 kW

+

†

Figure 16. Basic Regulation Configuration