ISL88705 INTERSIL [Intersil Corporation], ISL88705 Datasheet - Page 11

• Manufacturer Part Number: ISL88705
• Description: uP Supervisor with Watchdog Timer, Power-Fail Comparator, Manual Reset and Adjustable Power-On Reset
• Manufacturer: INTERSIL [Intersil Corporation]

Bipolar Voltage Sensing
Any of the ISL88705 - ISL88813 devices can be used to
sense and report the presence of both a positive and
negative voltage via the PFI and PFO as shown in Figure 16.
The V
PFI monitors the presence of the negative supply. As the
differential voltage across the R1, R2 divider is increased the
resistor values must be chosen such that the PFI node is
<1.25V when the -V supply is satisfactory and the positive
supply is at its maximum specified value. This allows the
positive supply to fluctuate within its acceptable range
without signaling a reset. Driving the MR with the inverted
PFO signal as shown provides for reset generation when -V
is not satisfactorily present. Reset will remain asserted as
long as PFO is high.
DD
monitors the positive voltage as normal and the
FIGURE 15. ISL88075EVAL1
ISL88705, ISL88706, ISL88707, ISL88708, 8SL88716, ISL88813
11
Special Application Considerations
Using good decoupling practices will prevent transients
(i.e., due to switching noises and short duration droops in the
supply voltage) from causing unwanted resets.
When using the C
layout as much as possible in order to minimize its effect on
the t
+5V
-5V
POR
R1
R2
timing.
FIGURE 16. ±5V MONITORING
POR
PFI
V+
pin, avoid stray capacitance during
V-
RESET
ISL8870X
V
DD
PFO
RST
MR
100k
December 6, 2006
2N3904
100k
FN8092.3