AD8214

Data Sheet

Rev. A | Page 12 of 16

APPLICATIONS

TYPICAL SETUP AND CALCULATIONS

The key feature of the AD8214 is its ability to detect an overcurrent

condition on the high side of the rail and provide a signal in less

than 100 ns. This performance protects expensive loads, FETs, and

shunt resistors in a variety of systems and applications. This section

details a typical application in which the normal current in the

system is less ≤10 A and an overcurrent detection is necessary

when 15 A is detected in the path.

common-mode voltage range of 5 V to 65 V, the typical voltage

across the shunt resistor is

10 A × 0.005 Ω = 50 mV

The voltage drop across the shunt resistor, in the case of an

overcurrent condition is

15 A × 0.005 Ω = 75 mV

The threshold voltage, must therefore be set at 75 mV,

corresponding to the overcurrent condition. R1 and R2 can be

selected based on this 75 mV threshold at the positive input of

the comparator.

A low load current across the regulator corresponds to optimal

regulator performance; therefore, the series resistance of R1 and

R2 must be relatively large. For this case, the total resistance can

be set as

R1 + R2 = 200 kΩ

To have a 75 mV drop across R1, the following calculations apply:

µA

12

k

200

2.4V =

Ω

R1

k

6.25

µA

12

mV

75

=

Ω

=

R2 = (200 kΩ – R1) = 193.75 kΩ

The values for R1 and R2 are set; correspondingly, the threshold

voltage at +IN is set at 75 mV.

Under normal operating conditions, the current is 10 A or less,

corresponding to a maximum voltage drop across the shunt of

50 mV. This means that the negative input of the comparator is

50 mV below the battery voltage. Since the positive input is

75 mV below the battery voltage, the negative input is at a

higher potential than the positive; therefore, the output of the

AD8214 is low.

If the current increases to 15 A, the drop across the shunt is

75 mV. As the current continues to increase, the positive input

of the comparator reaches a higher potential than the negative,

and the output of the AD8214 switches from low to high. The

input-to-output response of the AD8214 is less than 100 ns. The

output resistor in this case is selected so that the logic level high

signal is 3.3 V.

The output changes states from low to high in the case of an

overcurrent condition. However, the input offset voltage is

typically 1 mV; therefore, this must be taken into consideration

when choosing the threshold voltage. When the current in the

system drops back down to normal levels, the AD8214 changes

states from high to low. However, due to the built-in 10 mV

hysteresis, the voltage at (–IN) must be 10 mV higher than the

threshold for the output to change states from high to low. This

built-in hysteresis is intended to prevent input chatter as well as

any false states.

Table 4 shows typical resistors combinations that can be used to set

Table 4.

Threshold (mV)

R1 (kΩ)

R2 (kΩ)

30

1.5

120

50

1.6

75

60

2

80

75

2.4

75

110

8.06

169

BATTERY

(0.005Ω)

C1

0.01µF

R2

193.75kΩ

R1

6.25kΩ

2.4V

REGULATOR

1

3

6

5

8

2

I

Figure 30. Typical Application