TC7662BEOA713

The TC7662B is a pin-compatible upgrade to the Industry standard TC7660 charge pump voltage converter. It converts a +1.5V to +15V input to a corresponding – 1.5 to – 15V output using only two low-cost capacitors, eliminating inductors and their associated cost, size and EMI.

The on-board oscillator operates at a nominal frequency of 10kHz. Frequency is increased to 35kHz when pin 1 is connected to V+, allowing the use of smaller external capacitors. Operation below 10kHz (for lower supply current applications) is also possible by connecting an external capacitor from OSC to ground (with pin 1 open).

The TC7662B is available in both 8-pin DIP and 8-pin small outline (SO) packages in commercial and extended temperature ranges.

The TC7662B contains all the necessary circuitry to complete a negative voltage converter, with the exception of two external capacitors which may be inexpensive 1μF polarized electrolytic types. The mode of operation of the device may be best understood by considering Figure 2, which shows an idealized negative voltage converter. Capacitor C1 is charged to a voltage V+ for the half cycle when switches S1 and S3 are closed. (Note: Switches S2 and S4 are open during this half cycle.) During the second half cycle of operation, switches S2 and S4 are closed, with S1 and S3 open, thereby shifting capacitor C1 negatively by V+ volts. Charge is then transferred from C1 to C2 such that the voltage on C2 is exactly V+, assuming ideal switches and no load on C2. The TC7662B approaches this ideal situation more closely than existing non-mechanical circuits.

In the TC7662B, the four switches of Figure 2 are MOS power switches; S1 is a P-channel device and S2, S3 and S4 are N-channel devices. The main difficulty with this approach is that in integrating the switches, the substrates of S3 and S4 must always remain reverse biased with respect to their sources, but not so much as to degrade their “ON” resistances. In addition, at circuit start up, and under output short circuit conditions (VOUT = V+), the output voltage must be sensed and the substrate bias adjusted accordingly. Failure to accomplish this would result in high power losses and probable device latchup.

The problem is eliminated in the TC7662B by a logic network which senses the output voltage (VOUT) together with the level translators, and switches the substrates of S3 and S4 to the correct level to maintain necessary reverse bias.

The voltage regulator portion of the TC7662B is an integral part of the anti-latchup circuitry; however, its inherent voltage drop can degrade operation at low voltages. Therefore, to improve low voltage operation, the “LV” pin should be connected to GND, disabling the regulator. For supply voltages greater than 3.5 volts, the LV terminal must be left open to insure latchup proof operation and prev