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Data Sheet
PT7M7433/34/35
µP
Supervisory Circuit
Description
The PT7M7433/34/35 are single-level battery monitors
with internal hysteresis. These devices are offered with
single low-battery output indicators which can be used to
indicate three battery conditions: good (operate system in
normal mode), weak (operate system in low-power
mode), or empty (disable the system).
The PT7M7433/34/35 are user-adjustable threshold
voltages permitting the user to select the hysteresis range
and consequently the sensitivity of the system to noise. A
wide hysteresis range also prevents chattering that can
result due to battery recovery after load removal.
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Features
•
•
•
•
•
•
•
User-Adjustable Low/High Thresholds with 615mV
Internal Reference
Low Current (0.9µA typ)
Single Low-Battery Outputs
Push-Pull LBO, Open-Drain LBO and Open-Drain
LBO options
90ms Minimum LBO Timeout Period
Immune to Short Battery Voltage Transients
-40°C to + 85°C Operating Temperature Range
Applications
•
Monitoring lithiumion (Li+) cells or multicell
alkaline/ NiCd/ NiMH power supplies.
Ordering Information
Part Number
PT7M7433TA
PT7M7434TA
PT7M7435TA
PT7M7433TAE
PT7M7434TAE
PT7M7435TAE
Package
SOT23-5
SOT23-5
SOT23-5
SOT23-5(lead-free)
SOT23-5(lead-free)
SOT23-5(lead-free)
Table 1.
Function comparison of PT7M7433/34
Output
Item
Part No.
Open-Drain
Push-Pull
Single
Active high Active low Active low
1
PT7M7433
-
-
√
√
2
PT7M7434
-
-
√
√
3
PT7M7435
-
-
√
√
Threshold
Factory
User
fixed
adjustable
-
√
-
√
-
√
Package
Dual
-
-
-
SOT23-5
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Data Sheet
PT7M7433/34/35
µP
Supervisory Circuit
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Block Diagram
PT7M7433/34/35Block Diagram
VCC
R1
LTHIN
R
HTHIN
S
R3
VCC
615
mV
LBO TIMOUT
PERIOD
Q
LBO
(LBO)
Q
VCC
R2
EXTERNAL
RESISTOR-
DRIVER
LBO: PT7M7433/34
LBO: PT7M7435
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Data Sheet
PT7M7433/34/35
µP
Supervisory Circuit
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Pin Configuration
PT7M7433
PT7M7434
1
HTHIN
VCC
5
1
PT7M7435
HTHIN
VCC
5
2
GND
2
GND
3
LTHIN
LBO
4
3
LTHIN
LBO
4
Pin Description
Pin
7433/34/35
4
Name
LBO/LBO
Type
Description
Low-Battery Output.
LBO /LBO is asserted when LTHIN drops below
V
LTHIN
, and remains asserted for at least 90ms HTHIN rises above V
HTHIN
.
Push-pull output for PT7M7433. Open drain output for PT7M7434/35.
HTH Threshold Monitor Input.
A resistor-divider network sets the high
threshold associated with LBO/LBO.
LTH Threshold Monitor Input.
A resistor-divider network sets the low
threshold associated with LBO/LBO.
Supply Voltage.
Device power supply for adjustable threshold versions.
Ground
O
1
3
5
2
HTHIN
LTHIN
VCC
GND
I
I
P
P
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Data Sheet
PT7M7433/34/35
µP
Supervisory Circuit
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).
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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 Selection).
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
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.
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 Selection).
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).
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Data Sheet
PT7M7433/34/35
µP
Supervisory Circuit
Application Information
Resistor-Value Selection (Programming the
Adjustable Thresholds)
V
REF
= V
LTHIN
= V
HTHIN
= 615mV
V
TRIPLOW
= V
LTH
= V
REF
( R1 + R2 + R3 )
R2 + R3
R1 + R2 + R3 )
V
TRIPHIGH
= V
HTL
= V
REF
(
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
5MΩ.
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
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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 Selection).
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
LTH
t
LBCP
LBO
HTH – Battery voltage good enable operation
LTH – Battery voltage low suspend/disable operation
V
HYST
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