adm1070art Analog Devices, Inc., adm1070art Datasheet - Page 11

• Manufacturer Part Number: adm1070art
• Description: -48 V Hot Swap Controller
• Manufacturer: Analog Devices, Inc.

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/
OV glitch filter time, t
is set by the choice of external capacitor C
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 kΩ 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.
REV. 0
R1 (for R2 = 1 k )
Resistor Ratio
k
30
33
36
39
43
47
51
FLT
, do not force the gate drive low (t
V
Table IV. Resistance Ratios and Operating Voltage Windows
UV
(Falling)
26.7
29.2
31.8
34.4
37.8
41.3
44.7
V
T
, see Table III). The
Undervoltage
FLT
V
UV
28.2
31.0
33.7
36.4
40.0
43.7
46.4
(Rising)
–11–
V
Voltage Divider:
V
For R2 = 1 kΩ:
V
And for R1 = 39 kΩ:
V
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
Figure 4. Operating Voltage Window vs. Resistance Ratio
UV/OV
SS
SS
= V
= 40 V
= V
UV/OV
120
100
80
60
40
20
0
SS
UV/OV
30
(R2/(R1 + R2))
(R1 + 1)
V
OV
33
100.4
(Falling)
59.8
65.6
71.4
77.2
84.9
92.6
V
36
R1 – k
Overvoltage
39
(FOR R2 = 1k )
Figure 3. Voltage Divider
43
V
OV
–
+
102.4
V
(Rising)
SS
61.0
67.0
72.9
78.8
86.7
94.6
ADM1070
V
47
R1
R2 V
UV/OV
+
–
51