LT1054

SWITCHEDCAPACITOR VOLTAGE CONVERTERS

WITH REGULATORS

SLVS033F − FEBRUARY 1990 − REVISED NOVEMBER 2004

10

POST OFFICE BOX 655303

PRINCIPLES OF OPERATION

temperature coefficient (TC) of the reference voltage has been adjusted so that the TC of the regulated output voltage

is near zero. As seen in the typical performance curves, this requires the reference output to have a positive TC. This

nonzero drift is necessary to offset a drift term inherent in the internal reference divider and comparator network tied

to the feedback terminal. The overall result of these drift terms is a regulated output that has a slight positive TC at

output voltages below 5 V and a slight negative TC at output voltages above 5 V. For regulator feedback networks,

reference output current should be limited to approximately 60

to ground and does not affect the internal reference/regulator. This terminal also can be used as a pullup for LT1054

circuits that require synchronization.

is unidirectional, as should be expected when using bipolar switches.

OSC can be used to raise or lower the oscillator frequency or to synchronize the device to an external clock. Internally,

current sources of

±7 µA, so that the duty cycle is approximately 50%. The LT1054 oscillator is designed to run in

the frequency band where switching losses are minimized. However, the frequency can be raised, lowered, or

synchronized to an external system clock if necessary.

The frequency can be increased by adding an external capacitor (C2 in Figure 15) in the range of 5−20 pF from CAP+

times and raises the oscillator frequency. Synchronization can be accomplished by adding an external pullup resistor

used to drive OSC at the external clock frequency as shown in Figure 15.

the charge and discharge times, which lowers the oscillator frequency.

C1

LT1054

VOUT

VREF

OSC

VCC

CAP−

GND

CAP+

FB/SD

C2

VIN

Pin numbers shown are for the P package.

+

1

2

3

4

8

7

6

5

Figure 15. External-Clock System