HT7660 datasheet(4/9 Pages) HOLTEK

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HT7660

November 30, 1999

Functional Description

HT7660 needs only two external polarized elec-

trolytic capacitors to complete a negative volt-

age converter.

HT7660 has four MOS power switches: S1, S2,

S3 and S4. For the first half cycle, when S2 and

S4 are open, Capacitor C1 is charged to a volt-

age VDD through S1 and S3. During the second

half cycle, when S1 and S3 are open, the charge

on Capacitor C1 is shifted to Capacitor C2

through S2 and S4. Thereby, the voltage across

Capacitor C2 is VDD. Because the positive ter-

minal of C2 is connected to VSS, we get a -VDD

voltage at VOUT pin.

For high voltage operation, the LV pin is left

floating to enable the voltage regulator. This

can reduce the current consumption of the RC

oscillator, and thus get a fixed switching fre-

quency Fosc with high voltage range. For low

voltage operation, the LV pin is connected to

VSS to bypass the voltage regulator of which in-

herent voltage drop can degrade the operation

at low voltages.

A capacitor may be connected between VDD and

pin OSC to lower the switching Fosc, and an ex-

ternal clock may be added to replace the

built-in RC oscillator.

V DD

V SS

CA P +

CA P -

V SS

V OU T = - V DD

The operating mode of HT7660

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