ICL7665S_06 Datasheet, PDF (11/14 Pages) Intersil Corporation – CMOS Micropower Over/Under Voltage Detector

ICL7665S
UNREGULATED
DC INPUT
4700µF
7805
5V REGULATOR
5.86kΩ
715kΩ
130kΩ
HYST1
V+
HYST2
ICL7665S
V_SET1
V_SET2
OUT1
OUT2
470µF
BACKUP
BATTERY
22MΩ
2.2MΩ
1MΩ
1MΩ
1MΩ
RESET OR
WRITE
ENABLE
POWER
FAIL
WARNING
FIGURE 15. POWER FAIL WARNING AND POWERUP/POWERDOWN RESET
Simple High/Low Temperature Alarm
Figure 16 illustrates a simple high/low temperature alarm
which uses the ICL7665S with an NPN transistor. The
voltage at the top of R₁ is determined by the V_BE of the
transistor and the position of R₁’s wiper arm. This voltage
has a negative temperature coefficient. R₁ is adjusted so
that V_SET2 equals 1.3V when the NPN transistor’s
temperature reaches the temperature selected for the high
temperature alarm. When this occurs, OUT2 goes low. R₂ is
adjusted so that V_SET1 equals 1.3V when the NPN
transistor’s temperature reaches the temperature selected
for the low temperature alarm. When the temperature drops
below this limit, OUT1 goes low.
AC Power Fail and Brownout Detector
Figure 17 shows a circuit that detects AC undervoltage by
monitoring the secondary side of the transformer. The
capacitor, C₁, is charged through R₁ when OUT1 is OFF.
With a normal 100 VAC input to the transformer, OUT1 will
discharge C₁ once every cycle, approximately every 16.7ms.
When the AC input voltage is reduced, OUT1 will stay OFF,
so that C₁ does not discharge. When the voltage on C₁
reaches 1.3V, OUT2 turns OFF and the power fail warning
goes high. The time constant, R₁C₁, is chosen such that it
takes longer than 16.7ms to charge C₁ 1.3V.
11
FN3182.8
April 5, 2006