REV. 0

ADM1070

–11–

UNDERVOLTAGE/OVERVOLTAGE DETECTION

The ADM1070 incorporates single-pin overvoltage and

undervoltage detection with a programmable operating voltage

window. When the voltage on the UV/OV pin rises above the

OV rising threshold or falls below the UV falling threshold, a

fault signal is generated that disables the linear current regulator

and results in the GATE Pin being pulled low. The voltage fault

signal is time filtered so that faults of duration less than the UV/

filter operates only on the “faulting” edge (i.e., on a high to

low transition on the undervoltage monitor and on a low to

high transition on the overvoltage monitor). The analog com-

parators have some hysteresis to provide smooth switching of

the comparator inputs.

If the voltage on UV/OV goes out of range (i.e., below 0.86 V

or above 1.97 V) gate is pulled low. If the UV/OV voltage

subsequently re-enters the operating voltage window, the

ADM1070 will restore the gate drive.

The overvoltage and undervoltage thresholds are:

UV turning on = 0.91 V

UV turning off = 0.86 V

OV turning on = 1.97 V

OV turning off = 1.93 V

The undervoltage/overvoltage levels are determined by selection

of the resistor ratio R1/R2, (see Table I). These two resistors

form a resistor divider that generates the voltage; at the UV/OV

Pin, which is proportional to the supply voltage. By choosing

this ratio carefully, the ADM1070 can be programmed to apply

the supply voltage to the load only when it is within specific

thresholds. For example, for R1 = 39 k

Ω and R2 = 1 kΩ the

typical operating range is 36.4 V to 76.8 V. The undervoltage

and overvoltage shutdown thresholds are 34.4 V and 77.2 V

for this resistor ratio. 1% resistors should be used to maintain

the accuracy of these threshold levels.

Voltage Divider:

For R2 = 1 k

Ω:

And for R1 = 39 k

Ω:

Operating Range:

UV => 40(0.91) = 36.4 V

OV => 40(1.93) = 77.2 V

UV/OV Shutdown Levels:

UV => 40(0.86) = 34.4 V

OV => 40(1.97) = 78.8 V

––

+

+

R1

R2 V

UV/OV

Figure 3. Voltage Divider

R1 – k

(FOR R2 = 1k )

0

36

40

20

80

60

100

120

30

47

51

33

43

39

Figure 4. Operating Voltage Window vs. Resistance Ratio

V

61.0

67.0

72.9

78.8

86.7

94.6

102.4

Resistor Ratio

Undervoltage

Overvoltage

k

30

33

36

39

43

47

51

Table IV. Resistance Ratios and Operating Voltage Windows

V

26.7

29.2

31.8

34.4

37.8

41.3

44.7

V

28.2

31.0

33.7

36.4

40.0

43.7

46.4

V

59.8

65.6

71.4

77.2

84.9

92.6

100.4