Charge Pump Voltage Converters

TJ7660

HTC

Jan. 2007-Rev 1.0

8

Output Ripple

ESR also affects the ripple voltage seen at the output. The total ripple is determined by 2

voltage drops:

Again, a low ESR capacitor will reset in a higher performance output.

Paralleling Devices

Any number of TJ7660 voltage converters may be paralleled to reduce output resistance. The

The resultant output resistance would be approximately:

Cascading Devices

The TJ7660 may be cascaded as shown to produced larger negative multiplication of the initial

supply voltage. However, due to the finite efficiency of each device, the practical limit is 10

devices for light loads. The output voltage is defined by:

where n is an integer representing the number of devices cascaded. The resulting output

Changing the TJ7660 Frequency

It may be desirable in some applications, due to noise or other considerations, to increase the

oscillator frequency. This is achieved by overdriving the oscillator from an external clock, as

shown in Figure 17. In order to prevent possible device latchup, a 1kΩ resistor must be used in

series with the clock output. In a situation where the designer has generated the external clock

frequency using TTL logic, the addition of a 10kΩ pullup resistor to V+ supply is required. Note

that the pump frequency with external clocking, as with internal clocking, will be 1/2 of the clock

frequency. Output transitions occur on the positive-going edge of the clock.

TJ7660