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2013-11-0003 PT0236-6 11/18/13
6
PT7M6832-6840
Ultra Low Voltage Detectors
Functional Description
Reset Output
The PT7M6832–PT7M6840 assert a reset to prevent code-
execution errors during power-up, power-down, or brownout
conditions. They also assert a reset signal whenever the Vcc
supply voltage falls below a preset threshold (PT7M6832–
PT7M6837) or RESET-IN falls below the adjustable threshold
(PT7M6838-PT7M6840), keeping reset asserted for a fixed
timeout delay (Table 2) after Vcc or RESET-IN has risen
above the reset threshold. The PT7M6832/6835/6838 use a
push-pull active-low output, the PT7M6833/6836/6839 have a
push-pull active-high output, and the PT7M6834/6837/ 6840
have an open-drain active- low output stage. Connect a pull-
up resistor on the PT7M6834/6837/ 6840’s RESET output to
any supply between 0 and 6V.
Manual Reset Input
Reset remains asserted while MR is low, and for a fixed
timeout delay after MR returns high. This input has an
internal 20kΩ pull-up resistor, so it can be left open if it is not
used. MR can be driven with CMOS logic level, or with open-
drain/collector outputs. To create a manual reset function,
connect a normally open momentary switch from MR to
ground; external debounce circuitry is not required.
RESET-IN
The PT7M6838/6839/6840 features a RESET-IN input for
monitoring supply voltages down to 0.44V. An external
resistive-divider network can be used to set voltage
monitoring thresholds as shown in Fig.3. As the monitored
voltage falls, the voltage at RESET-IN decreases and asserts a
reset when it falls below the RESET-IN threshold(V
RSTIN
).
The low-leakage current at RESET-IN allows for relatively
large-value resistors to be used, which reduce power
consumption. For example, for a 0.6V monitored trip level, if
R2 = 200kΩ, then R1 = 70.3kΩ.
Note: The minimum Vcc of 1.3V is required to guarantee the
RESET-IN threshold accuracy.
RESET
(RESET)
VREF=444mV
RESET-IN
V
CC
V
monitored
PT7M6838
/6839
/6840
R
1
R
2
R1=R2(Vmonitored/VREF-1)
() is for PT7M6839
Fig.3 External setting of adjustable threshold
