ISL28177

7

FN7859.2

April 5, 2012

Applications Information

Functional Description

The ISL28177 is a low noise op amp fabricated in a 40V

complementary bipolar DI process designed for general purpose

low power applications. It utilizes a super-beta NPN input stage

with input bias current cancellation for low input bias current and

low input noise voltage. A complimentary bipolar output stage

enables high capacitive load drive without external

compensation.

Operating Voltage Range

The ISL28177 is designed to operate over the 6V (±3V) to 40V

(±20V) range. The common mode input voltage range extends to

2V from each rail, and the output voltage swings to 1.3V of

each rail.

Input Performance

The super-beta NPN input pair reduces input bias current while

maintaining good frequency response, low input bias current and

low noise. Input bias cancellation circuits provide additional bias

current reduction to <1nA, and excellent temperature

Input ESD Diode Protection

The input terminals (IN+ and IN-) have internal ESD protection

diodes to the positive and negative supply rails, series connected

500Ω current limiting resistors and an anti-parallel diode pair

across the inputs (Figure 21).

The series resistors limit the high feed-through currents that can

occur in pulse applications when the input dv/dt exceeds the

0.2V/µs slew rate of the amplifier. Without the series resistors, the

input can forward-bias the anti-parallel diodes causing current to

flow to the output, resulting in severe distortion and possible diode

failure. Figure 17 provides an example of distortion free large signal

The series resistors enable the input differential voltage to be equal

to the maximum power supply voltage (40V) without damage.

In applications where one or both amplifier input terminals are at

risk of exposure to high voltages beyond the power supply rails,

current limiting resistors may be needed at the input terminal to

limit the current through the power supply ESD diodes to

20mA max.

Output Current Limiting

The output current is internally limited to approximately ±30mA

at +25°C and can withstand a short circuit to either rail as long

as the power dissipation limits are not exceeded. Continuous

operation under these conditions may degrade long term

reliability.

Output Phase Reversal

Output phase reversal is a change of polarity in the amplifier

transfer function when the input voltage exceeds the supply

voltage. The ISL28177 is immune to output phase reversal.

FIGURE 19. POSITIVE OUTPUT OVERLOAD RESPONSE TIME

FIGURE 20. NEGATIVE OUTPUT OVERLOAD RESPONSE TIME

-2

0

2

4

6

8

10

12

14

16

-280

-240

-200

-160

-120

-80

-40

0

40

80

0

40

80

120 160 200 240 280 320 360 400

TIME (µs)

OVERDRIVE = 1V

INPUT

OUTPUT

-16

-14

-12

-10

-8

-6

-4

-2

0

2

-80

-40

0

40

80

120

160

200

240

280

0

40

80

120 160 200 240 280 320 360 400

TIME (µs)

OVERDRIVE = 1V

INPUT

OUTPUT

FIGURE 21. INPUT ESD DIODE CURRENT LIMITING

-

+

V+

V-

500Ω

500Ω