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Data Sheet

PT7M7433/34/35 μ P Supervisory Circuit

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V TRIPLOW = V LTH = V REF ( )

V TRIPHIGH = V HTL = V REF ( )

Hysteresis

Hysteresis increases the comparator’s noise margin by

increasing the upper threshold or decreasing the lower

threshold (see blow). The hysteresis prevents the output from

oscillating (chattering) when V CC is near the low-battery

threshold. This is especially important for applications where

the load on the battery creates significant fluctuations in

battery voltages.

Adjustable Hysteresis (PT7M7433/34/35)

Block diagram shows the correct connections for the external

resistor-dividers. To adjust the low-battery threshold and

hysteresis connect resistor R1 between V CC and LTHIN,

resistor R2 between LTHIN and HTHIN, and R3 between

HTHIN and GND. The hysteresis for the PT7M7433/34/35 is

determined by an external resistor-divider network (see

Application information Resistor-Value Selectio n).

Application Information

Resistor-Value Selection (Programming the

Adjustable Thresholds)

V REF = V LTHIN = V HTHIN = 615mV

R1 + R2 + R3

R2 + R3

R1 + R2 + R3

R3

R TOTAL = R1 + R2 + R3

Use the following steps to determine values for R1, R2, and

R3 of Functional Block Diagram.

1) Choose a value for R TOTAL . Because the PT7M7433/34/35

have very high input impedance, R TOTAL can be up to

5M ? .

2) Calculate R3 based on R TOTAL and the desired upper trip

point:

R3 =

V REF × R TOTAL

V TRIPHIGH

=

615mV × R TOTAL

V TRIPHIGH

3) Calculate R2 based on R TOTAL , R3, and the desired lower

trip point:

R2 =

615mV × R TOTAL

V TRIPLOW

- R3

4) Calculate R1 based on RTOTAL, R3, and R2:

R1 = R TOTAL – R2 – R3

Fig 1. PT7M7433/34/35 adjustable hysteresis

V HTH

V BATT

V HYST

V LTH

t LBCP

LBO

HTH – Battery voltage good enable operation

LTH – Battery voltage low suspend/disable operation

PT0213(05/09)

5

Ver: 3