ICL7665S_06 Datasheet, PDF (9/14 Pages) Intersil Corporation – CMOS Micropower Over/Under Voltage Detector

R_P
R₂₁
R₃₁
R₁₁
V_IN
V+
OUT1
OUT2
HYST1 HYST2
SET1
SET2
ICL7665S
R_P
R₂₂
R₃₂
R₁₂
Applications
Single Supply Fault Monitor
Figure 12 shows an over/under voltage fault monitor for a
single supply. The overvoltage trip point is centered around
5.5V and the undervoltage trip point is centered around 4.5V.
Both have some hysteresis to prevent erratic output ON and
OFF conditions. The two outputs are connected in a wired
OR configuration with a pullup resistor to generate a power
OK signal.
+5V SUPPLY
FIGURE 11. AN ALTERNATIVE HYSTERESIS CIRCUIT
TABLE 1. SET-POINT EQUATIONS
NO HYSTERESIS
Overvoltage V_TRIP =
R₁₁ + R₂₁
R₁₁
Overvoltage V_TRIP =
R₁₂ + R₂₂
R₁₂
HYSTERESIS PER FIGURE 10A
V_U1 =
R₁₁ + R₂₁ + R31
R₁₁
x V_SET1
Overvoltage V_TRIP
V_L1 =
R₁₁ + R₂₁
R₁₁
x V_SET1
V_U2 =
R₁₂ + R₂₂ + R₃₂
R₁₂
x V_SET2
Undervoltage V_TRIP
V_L2 =
R₁₂ + R₂₂
R₁₂
x V_SET2
HYSTERESIS PER FIGURE 11
V_U1 =
R₁₁ + R₂₁
R₁₁
x V_SET1
Overvoltage V_TRIP
V_L1 =
R₁₁ +
R₂₁R₃₁
R₂₁ + R_{31 x VSET1}
R₁₁
V_U2 =
R₁₂ + R₂₂
R₁₂
x V_SET2
Overvoltage V_TRIP
V_L2 =
R₁₂ +
R₂₂R₃₂
R₂₂ + R₃₂ x V_SET2
R₁₂
x V_SET1
x V_SET2
R_{21 324kΩ}
13MΩ
5%
R₃₁
100kΩ
OPEN VOLTAGE
DETECTOR
V_U = 5.55V
V_L = 5.45V
V+
HYST1 HYST2
V_SET1 V_SET2
OUT1 OUT2
249kΩ R₂₂
R₃₂
7.5MΩ
5%
100kΩ
OPEN VOLTAGE
DETECTOR
V+
V_U = 4.55V
V_L = 4.45V
1MΩ
POWER
OK
FIGURE 12. FAULT MONITOR FOR A SINGLE SUPPLY
Multiple Supply Fault Monitor
The ICL7665S can simultaneously monitor several supplies
when connected as shown in Figure 13. The resistors are
chosen such that the sum of the currents through R_21A,
R_21B, and R₃₁ is equal to the current through R₁₁ when the
two input voltage are at the desired low voltage detection
point. The current through R₁₁ at this point is equal to
1.3V/R₁₁. The voltage at the V_SET input depends on the
voltage of both supplies being monitored. The trip voltage of
one supply while the other supply is at the nominal voltage
will be different that the trip voltage when both supplies are
below their nominal voltages.
The other side of the ICL7665S can be used to detect the
absence of negative supplies. The trip points for OUT1
depend on both the negative supply voltages and the actual
voltage of the +5V supply.
9
FN3182.8
April 5, 2006