10

FN6633.0

May 29, 2009

Applications Information

Functional Description

The ISL28127 and ISL28227 are single and dual, low noise

10MHz BW precision op amps. Both devices are fabricated

in a new precision 40V complementary bipolar DI process. A

super-beta NPN input stage with input bias current

cancellation provides low input bias current (1nA typical),

low input offset voltage (10µV typ), low input noise voltage

(3nV/

√Hz), and low 1/f noise corner frequency (3Hz). These

amplifiers also feature high open loop gain (1400V/mV) for

excellent CMRR (120dB) and THD+N performance

bipolar output stage enables high capacitive load drive

without external compensation.

Operating Voltage Range

The devices are designed to operate over the 4.5V (±2.25V)

to 40V (±20V) range and are fully characterized at 10V (±5V)

and 30V (±15V). Parameter variation with operating voltage

is shown in the “Typical Performance Curves” beginning on

page 5. The input common mode voltage sensitivity to

temperature is shown in Figure 19 (±15V). Figure 20 shows

VOS as a function of supply voltage and temperature with

the common mode voltage at 0V for split supply operation.

Input ESD Diode Protection

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

protection diodes to the positive and negative supply rails, and

an additional anti-parallel diode pair across the inputs

(Figures 26 and 27).

For unity gain applications (Figure 26) where the output is

connected directly to the non-inverting input a current limiting

protect the anti-parallel differential input protection diodes.

• The amplifier input is supplied from a low impedance

source.

• The input voltage rate-of-rise (dV/dt) exceeds the maximum

slew rate of the amplifier (±3.6V/µs).

If the output lags far enough behind the input, the anti-parallel

input diodes can conduct. For example, if an input pulse

ramps from 0V to +10V in 1µs, then the output of the

ISL28x27 will reach only +3.6V (slew rate = 3.6V/µs) while the

input is at 10V, The input differential voltage of 6.4V will force

input ESD diodes to conduct, dumping the input current

directly into the output stage and the load. The resulting

current flow can cause permanent damage to the ESD

diodes. The ESD diodes are rated to 20mA, and in the

limit the current to < 6.4mA, and provide additional protection

up to ±20V at the input.

In applications where one or both amplifier input terminals

are at risk of exposure to high voltage, current limiting

resistors may be needed at each input terminal (see

supply ESD diodes to 20mA.

Output Current Limiting

The output current is internally limited to approximately

±45mA at +25°C and can withstand an short circuit to either

rail as long as the power dissipation limits are not exceeded.

This applies to only 1 amplifier at a time for the dual op amp.

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 ISL28127 and ISL28227 are immune to output

phase reversal, even when the input voltage is 1V beyond

the supplies.

Power Dissipation

It is possible to exceed the +150°C maximum junction

temperatures under certain load and power supply

conditions. It is therefore important to calculate the

determine if power supply voltages, load conditions, or

package type need to be modified to remain in the safe

operating area. These parameters are related using

Equation 1:

FIGURE 26. INPUT ESD DIODE CURRENT LIMITING - UNITY

GAIN

-

+

V+

V-

FIGURE 27. INPUT ESD DIODE CURRENT LIMITING -

DIFFERENTIAL INPUT

-

+

V+

V-

T

JMAX

T

MAX

θ

+

=

(EQ. 1)

ISL28127, ISL28227