a) Internal difference amplifier with an example of a decoupling filter.

10

µs/div

10

µs/div

R

2

40k

Ω

R

1

10k

Ω

R

4

40k

Ω

R

3

10k

Ω

R

5

Dummy

Shunt

Differential

Amplifier

R

F

50

Ω

Decoupling, Low−Pass Filter

REF

IN

Compensated

REF

IN

ADC

V

OUT

C

F

10nF

R

SHUNT

I

COMP2

K2

DRV401 Differential Amplifier Section

NOTE: R

OVER-RANGE COMPARATOR

DRV401-EP

Figure 5. Internal Difference Amplifier With Example of a Decoupling Filter

High peak current can overload the differential amplifier connected to the shunt. The OVER-RANGE pin, an

open-drain output, indicates an over-voltage condition for the differential amplifier by pulling low. The output of

this flag is suppressed for 3

µs, preventing unwanted triggering from transients and noise. This pin returns to

high as soon as the overload condition is removed (external pull-up required to return the pin high).

This ERROR flag not only provides a warning about a signal clipping condition, but is also a window comparator

output for actively shutting off circuits in the system. The value of the shunt resistor defines the operating window

for the current. It sets the ratio between the nominal signal and the trip level of the Over-Range flag. The trip

current of this window comparator is calculated using the following example:

With a 5 V supply, the output voltage swing is approximately ±2.45 V (load and supply

voltage-dependent).

The gain of 4 V/V allows an input swing of ±0.6125 V.

See the differential amplifier curve of the Typical Characteristics, Output Voltage vs Output Current.

The over-range condition is internally detected as soon as the amplifier exceeds its linear operating range, not

just a set voltage level. Therefore, the error or the over-range comparator level is reliably indicated in fault

conditions such as output shorts, low load or low supply conditions. As soon as the output cannot drive the

voltage higher, the flag is activated. This configuration is a safety improvement over a voltage level comparator.

Copyright © 2008, Texas Instruments Incorporated

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