ISL70100SEH, ISL73100SEH

4. Functional Description

R34DS0009EU0101 Rev.1.01

Page 19 of 27

Jul.10.20

4.

Functional Description

The ISL70100SEH is a transconductance current sense amplifier with a power supply range of 2.7V to 40V. Its

input common-mode range extends from -0.3V to 40V, which makes it ideal for use in both low-side and high-side

applications. The input common-mode voltage is independent of the power supply such that the ISL70100SEH

can be powered of a 5V rail but sense a 40V common mode. The ISL70100SEH level shifts in the sensed voltage

from the sensed power supply to a ground-referenced output. The output gain of the ISL70100SEH can be easily

configured with a single resistor on the output. It outputs a current proportional to the input voltage differential and

the output resistor sets the voltage gain seen by downstream devices.

The ISL7x100SEH can be driven with bi-polar supplies with the positive voltage on V+ and the negative voltage

on V-. The same voltage differentials should still be between 2.7V and 40V from V+ to V-. The output of the

amplifier is referenced to V- so any downstream device will need to be able to handle a bipolar input.

4.1

Output Signal Range

The output range of these amplifiers is limited on the low end by the input offset voltage and the saturation voltage

of the output transistors on the top end. The maximum voltage is always about 2V below the voltage on V+. If the

application calls for a large gain, the supply voltage may need to be increased to accommodate the full output

voltage range. For example, if the supply voltage is 2.7V, the output can only get up to 0.7V before the output is

saturated; this sets the maximum gain with 2.7V supply to 4.67 with a maximum sensing voltage of 150mV. If the

sensing voltage range is reduced, higher gains can be used.

where:

•ACSA(MAX) is the maximum output gain given the maximum input differential

• V+ is the power supply voltage of the ISL7x100SEH in volts

•VOH is output high saturation voltage referred to V+ from the electrical specifications table in volts

•VSEN(MAX) is the maximum input differential that the application calls for in volts

Typically, the output of the ISL7x100SEH is connected to the input of an Analog-to-Digital Converter (ADC), which

has limited input voltage ranges. Ensure that the output voltage (IOUT(MAX)•ROUT) does not exceed the input

voltage range of the downstream ADC.

4.2

Input Common-Mode Range

The input common-mode range of the ISL70100SEH and ISL73100SEH ranges from -0.3V to 40V regardless of

the voltage on V+. The electrical specifications table shows that the offset voltage of these amplifiers changes

very slightly over the full common-mode range. The inputs are also capable of either RS+ or RS- dropping to 0V

without damaging the amplifier, this is particularly useful in monitoring protection fuse circuits where the output

goes to the positive rail if the fuse is blown. If the inputs differential is reversed (RS- goes above RS+), the output

does not phase invert, it will simply remain at the output low voltage specified in the electrical specifications table.

4.3

Crossover Region

The ISL7x100SEH accomplishes the wide input common-mode range using multiple input paths that are selected

based on the common-mode voltage. The transition point between the high-side and low-side is typically 1.7V but

can range from 1.5V to 2.0V across temperature. When the common-mode voltage has reached the transition

point, there is a soft switchover from the low-side to the high-side.

ACSA MAX



V+

 V

OH

–

VSEN MAX



--------------------------------

=

(EQ. 1)