ISL88705 Просмотр технического описания (PDF) - Renesas Electronics

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ISL88705

µP Supervisor with Watchdog Timer, Power-Fail Comparator, Manual Reset and Adjustable Power-On Reset

Renesas Electronics 

ISL88705, ISL88706, ISL88707, ISL88708, ISL88716, ISL88813

Bipolar Voltage Sensing

Any of the ISL88705, ISL88706, ISL88707, ISL88708,

ISL88716, 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 VDD monitors the

positive voltage as normal and the 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.

+5V

R1

VDD

MR

100k

100k

PFI

PFO

2N3904

R2

When using the CPOR pin, avoid stray capacitance during

layout as much as possible in order to minimize its effect on the

tPOR timing.

If using a voltage resistor divider on the PFI input to critique an

external voltage and intending to use the MR input to initiate

resets then avoid having the PFI voltage less than PFI Vth

+2.2V as unintended PFO transition may occur when MR is

transitioning high.

RST

-5V

ISL8870x, ISL88716, ISL88813

RESET

V+

V-

FIGURE 16. ±5V MONITORING

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.

FN8092 Rev 6.00

November 30, 2015

Page 12 of 16

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