PA22

12

PA22 REV C

Figure 17: Overvoltage Protection

POWER SUPPLY BYPASSING

Bypass capacitors to power supply terminals +VS and -VS must be connected physically close to the pins.

Apex recommends to use electrolytic capacitors of 10 µF or greater per output amp. As additional prevention

of local parasitic oscillation in the output stage of the PA22, Apex advises to place high quality ceramic capac-

itors (X7R) of 0.1 µF or greater in parallel to the electrolytic capacitors.

PHASE COMPENSATION

The external compensation capacitor CC is connected between pins 3 and 4. Unity gain stability can be

achieved with any capacitor value larger than 220 pF for a minimum phase margin of 45° driving resistive

loads. At higher gains, more phase shift can usually be tolerated, and the compensation capacitor value can

be reduced to result in higher bandwidth and slew rate. Use the typical operating curves as a guide to select

CC for the application. An NPO (COG) type capacitor rated for the full supply voltage (250 V) is required.

TEMPERATURE SENSE

PA22 offers accurate junction-temperature sense. This uses two parallel bipolar transistors mounted

directly on top of select power die for near-junction temperature measurement. Connect pins 12 and 13 to

the D- and D+ pins of LTC2997 (or similar device), respectively. The LTC2997 will properly bias the bipolar

transistors and translate the signal to a Proportional To Absolute Temperature (PTAT) voltage. Apex does not

recommend reading temperature without an LTC2997 or similar device.

+IN

-IN

Q1

Q2

Q3

Q4

Z1

Z2

-VS

+VS