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Data Sheet

PT7M7433/34/35 μ P Supervisory Circuit

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Function Description

The PT7M7433/34/35 are available with user adjustable

monitoring.

The user sets the threshold voltages for the PT7M7433/34/35,

which permit the user to select the hysteresis range, and

consequently the sensitivity of the system to noise. A wide

hysteresis range prevents chattering that can result during

battery recovery or load removal. The PT7M7433/34/35 have

single low-battery outputs.

The PT7M7433/34/35 combine a 615mV reference with two

comparators, logic, and timing circuitry to provide the user

with information about the charge state of the power-supply

batteries. The PT7M7433/34/35 monitor separate high-voltage

and low-voltage thresholds to determine battery status. The

output can be used to signal when the battery is charged, when

the battery is low, and when the battery is empty.

PT7M7433/34/35 are also available with thresholds

determined using an external resistor-divider (see Application

information Resistor-Value Selectio n). The adjustable versions

can monitor down to 0.62V, making them suitable for

monitoring single-cell alkaline, NiMH, and NiCd applications

(V CC ≥ 1.8V).

When the power-supply voltage drops below the specified low

threshold, the low-battery output asserts (see Low-Battery

Outpu t). When the voltage rises above the specified high

threshold following a 90ms (min) time-out period, the low-

battery output is deasserted (see Threshold Monitorin g). This

ensures the supply voltage has stabilized before power-

converter or microprocessor activity is enabled.

PT0213(05/09)

4

Low-Battery Output

The low-battery outputs are available in active-low (LBO,

push-pull and open-drain) and action-high (LBO open-drain)

configurations. Push-pull outputs are referenced to V CC (for

adjustable threshold versions).

The open-drain devices can be pulled to a voltage independent

of V CC or BATT, up to 5.5V. This allows the device to

monitor and operate from direct battery voltage while

interfacing to higher voltage microprocessors.

The PT7M7433/34/35 single-output voltage monitors provide

a single low-battery output, LBO/LBO. The PT7M7433/34

adjustable-threshold parts assert LBO/LBO when the LTHIN

input drops below the V LTHIN threshold (615mV).

Threshold Monitoring

The PT7M7433/34/35 HTHIN and LTHIN inputs are high-

impedance inputs to comparators. An external resistor divider

network is required between the monitored voltage, HTHIN,

LTHIN, and GND to select the desired thresholds (see

Application information Resistor-Value Selectio n). The

PT7M7433/34/35 single-output voltage monitors assert LBO

/LBO when LTHIN drops below the internal LTHIN reference

(615mV). LBO/LBO is deasserted when HTHIN rises above

the internal HTHIN reference level (615mV) for at least 90ms

(see AC Electrical Characteristics: Fig 2).

Ver: 3