7

LT1462/LT1463

Phase Reversal Protection

Most industry standard JFET input single, dual and quad

op amps exhibit phase reversal at the output when the

negative common mode limit at the input is exceeded.

Common mode range is at a premium at

±5Vsupplies.The

Figures show a

±5.2V sine wave input (Figure 1a), the

(1a)

±5.2V Sine Wave

LT1462 • F01a

LT1462 • F01b

LT1462 • F01c

(1b) Typical JFET Input Op Amp

with

±5V Supplies

(1c) LT1462/LT1463 Output

with

±5V Supplies

response of a competing JFET input op amp in the unity-

gain follower mode (Figure 1b) and the response of the

LT1462/LT1463 (Figure 1c).

The phase reversal of Figure 1b can cause lock-up in servo

systems.TheLT1462/LT1463doesnotphase-reversewhen

the common mode input is anywhere within the supplies.