AD8214

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THEORY OF OPERATION

The AD8214 is a high voltage comparator offering an input-to-

output response time of less than 100 ns. This device is ideal for

detecting overcurrent conditions on the high side of the control

loop. The AD8214 is designed specifically to facilitate and allow

for fast shutdown of the control loop, preventing damage due to

excessive currents to the FET, load, or shunt resistor.

The AD8214 operates with a supply of 5 V to 65 V. It combines

a fast comparator, optimized for high side operation, with a

2.4 V series voltage regulator. The regulator provides a stable

voltage that is negative with respect to the positive supply rail,

and it is intended to provide power to the internal electronics,

set a comparison threshold below the supply rail, and power

small application circuits used with the comparator.

The differential input of the comparator may be operated at, or

slightly above or below, the positive supply rail. Typically, one of

the comparator inputs is driven negative with respect to the

positive supply by a small series resistor carrying the main

supply current to the load. The other input of the comparator

connects to a voltage divider across the regulator, so the

comparator trips as the voltage across the series resistor crosses

the user-selected threshold.

The AD8214 features a current output. The current is low (100 nA

typical), until the user selected threshold is crossed. After this point

the output switches to high (1 mA typical). The current output

current easily drives a ground referenced resistor to develop logic

levels determined by the value of the load resistor.

The comparator input is balanced to switch as the inverting

input (–IN) is driven negative with respect to the noninverting

input (+IN). As the comparator output switches from 0 mA to

1 mA, a small hysteresis (10 mV) is activated to minimize the

effects of noise in the system that may be triggered by the

comparator signal. This means that to restore the output to zero,

the input polarity must be reversed by 10 mV beyond the

original threshold.

1

3

2

BATTERY

SHUNT

TO LOAD

+

_

CONSTANT

THRESHOLD

VOLTAGE DROP

ACROSS SHUNT

CORRESPONDING

TO CURRENT LEVEL

+

_

R1

R2

2.4V

REGULATOR

1

3

6

5

8

2

CONSTANT

2.4V

UP TO 65V

I

Figure 28. Simplified Schematic