PT7M7436 Datasheet, PDF (4/6 Pages) Pericom Semiconductor Corporation – Supervisory Circuit

PT7M7436/37/38
P Supervisory Circuit
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Block Diagram
VCC
R1
LTHIN
VCC
R2
HTHIN
R3
VCC
615
mV
HYSTERESIS SWITCH
LBO
TIMOUT
PERIOD
LBOL
(LBOL)
LBOH
(LBOH)
HYSTERESIS SWITCH
LBOL/LBOH: PT7M7436/37
LBOL/LBOH: PT7M748
Function Description
The PT7M7436/37/38 are available with user adjustable
monitoring.
The PT7M7436/37/38 combine a 585/615mV reference with
two comparators, logic, and timing circuitry to provide the
user with information about the charge state of the power-
supply batteries. The PT7M7436/37/38 monitor separate high-
voltage and low-voltage thresholds to determine battery status.
The outputs can be used to signal when the battery is charged,
when the battery is low, and when the battery is empty.
PT7M7436/37/38 are also available with thresholds
determined using an external resistor-divider (see Application
information Resistor-Value Selection). They 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
Output). When the voltage rises above the specified high
threshold following a 90ms (min) time-out period, the low-
battery output is deasserted (see Threshold Monitoring). This
ensures the supply voltage has stabilized before power-
converter or microprocessor activity is enabled.
The open-drain devices can be pulled to a voltage independent
of V_CC, up to 5.5V. This allows the device to monitor and
operate from direct battery voltage while interfacing to higher
voltage microprocessors.
The PT7M7436/37/38 dual-output voltage monitors provide
two low-battery outputs, LBOH/LBOH and LBOL/LBOL.
They will assert LBOH /LBOH when HTHIN drops below
V_HTHIN-, and assert LBOL/LBOL when LTHIN drops below
V_LTHIN-.
Threshold Monitoring
The PT7M7436/37/38 dual-output voltage monitors assert
LBOL/LBOL when LTHIN drops below the LTHIN-
threshold and deassert LBOL/LBOL when LTHIN rises above
the LTHIN+ threshold for at least 90ms. LBOH/LBOH is
asserted when HTHIN drops below the HTHIN- threshold and
is deasserted when HTHIN rises above the HTHIN+ threshold
for at least 90ms (see AC Electrical Characteristics: Fig 1).
Hysteresis
Low-Battery Output
Hysteresis increases the comparator’s noise margin by
increasing the upper threshold or decreasing the lower
The low-battery outputs are available in active-low (LBOH,
LBOL push-pull and open drain) and active-high (LBOH,
LBOL open drain) configurations. Push-pull outputs are
referenced to V_CC.
threshold. 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. The
hysteresis for the PT7M7436/37/38 is the differences between
V_HTHIN- and V_HTHIN+ (1.05) or V_LTHIN- and V_LTHIN+ (1.05).
12-07-0002
PT0212-6
07/05/12
4