Preliminary Data Sheet
PT7M7479 Voltage Detector
with Adjustable Hysteresis
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Features
General
•
Optimized for PDAs, cellular telephones, pagers, and
other battery-powered devices
•
Independently adjustable high- and low-Voltage
thresholds
•
High 2% voltage threshold accuracy; 1% available
The PT7M7479 is a voltage monitor - uniquely designed
to detect two separate voltage thresholds - combined
with a delay generator and logic. It is designed for
monitoring the battery supply of portable digital systems,
particularly PDAs, pagers, and cellular telephones.
•
Assured Reset at VCC = 1.2V
•
Extremely low 1µA typical supply current
•
Built in 140ms (minimum) delay deglitches output
•
Immune to brief power supply transients
High- and low-voltage thresholds can be adjusted
independently, allowing for wide hysteresis. Voltage
detection thresh-olds are accurate to 2%. If the battery
voltage falls below the low-voltage threshold, the output
RST or RST is asserted and latched, preventing system
operation until the battery is replaced or recharged.
Internal logic prevents the output from chattering due to
battery recovery or load removal. The output is asserted
for140ms (minimum) when a fresh battery is inserted.
Applications
•
Portable digital systems
•
Particularly PDAs, pagers
•
Cellular telephones
The IC’s power supply input is separate from the
detector inputs, allowing the PT7M7479 to be powered
from a down-stream supply, such a boost converter.
Ordering Information
Part Number
Package
PT7M7479HAT
SOT23-5
PT7M7479HBT
SOT23-5
PT7M7479LAT
SOT23-5
PT7M7479LBT
SOT23-5
Supply current is extremely low (1µA, typical), making
it ideal for portable applications. A high-precision 1%
grade is available.
Block Diagram
VCC
VBATT
+
LTH
-
VLO
R Q
One Shot
VHI
HTH
+
-
+
-
Delay
Line
RST
(PT7M7479L)
S Q
RST
(PT7M7479H)
1.240V
Bandgap
Reference
GND
PT0182(06/04)
Ver: 0
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Preliminary Data Sheet
PT7M7479 Voltage Detector
with Adjustable Hysteresis
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Function comparison
Part Number
Output Polarity
Accuracy
Temperature Range
PT7M7479HAT
Active-High RST
1%
–40°C to +85°C
PT7M7479HBT
Active-High RST
2%
–40°C to +85°C
PT7M7479LAT
Active-Low RST
1%
–40°C to +85°C
PT7M7479LBT
Active-Low RST
2%
–40°C to +85°C
Pin Configuration
PT7M7479H
PT7M7479L
1
HTH
2
GND
3
LTH
Vcc
5
RST
(RST) 4
SOT23-5
Pin Description
Pin
Name Type
PT7M
7479H
PT7M
7479L
1
1
HTH
I
2
2
GND
P
3
3
LTH
I
Description
High-Voltage Threshold Input: Analog input to a comparator. When the level on this pin
initially rises above VREF, the delay generator cycles and the RST remains low or RST remains
high for a minimum of 140ms.
Ground
Low-Voltage Threshold Input: Analog input to a comparator. This is the voltage monitor
input assigned to detect a low voltage condition. When the level on this pin falls below VREF, RST
or RST is asserted and the condition is latched until V HTH > VREF.
Reset Output: Push-pull output. This output is asserted and latched when
4
5
RST
O
4
RST
O
5
Vcc
P
VLTH <VREF, indicating a low voltage condition. This state remains latched until VHTH > V REF.
The polarity of this signal (active-high or low) is determined by the part number suffix. See
Function comparison.
Reset Output: Push-pull output. This output is asserted and latched when VLTH <VREF,
indicating a low voltage condition. This state remains latched until VHTH > VREF. The polarity of
this signal (active-high or low) is determined by the part number suffix. See Function comparison.
Power Supply: Independent supply input for internal circuitry.
PT0182(06/04)
Ver: 0
2
Preliminary Data Sheet
PT7M7479 Voltage Detector
with Adjustable Hysteresis
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Function Description
Application Information
The PT7M7479 monitors the voltage of a battery and detects
when it is discharged below a programmed level. Upon being
replaced, or being recharged above a second higher programmed
trip point, the output remains low (PT7M7479L) or high
(PT7M7479H) for a minimum of 140ms and then sends a reset
signal to a microprocessor or other downstream component. See
“Timing Diagram.”
Resistor-Value Selection (Programming the
Adjustable Thresholds)
The low-voltage threshold is calculated as using:
VBAT (lo) = VREF (
R1 + R2 + R3
)
R2 + R3
The high-voltage threshold is calculated as using:
RST, RST Low Output
R1 + R2 + R3
)
R3
The output is a push-pull logic signal which is asserted when the
PT7M7479 detects a low input voltage. The PT7M7479L’s RST
output is active-low; the PT7M7479H’s RST output is activehigh.
VBAT (hi) = VREF (
Trip Points
To minimize battery current draw it is recommended to use 1
MΩ as the total resistor value
RTOTAL = R1 + R2 + R3.
Battery voltage is monitored by a comparator via a voltage
divider network. The divided voltage is compared to an internal
reference voltage. When the voltage at the LTH input pin drops
below the internal reference voltage, the output is asserted. At
this point, the voltage at HTH is assumed to be below the
reference voltage.
Delay
Where, for both equations:
VREF = 1.240 V
Input Transients
The PT7M7479 is inherently immune to very short negativegoing “glitches.” Very brief transients may exceed the VBAT(lo)
threshold without tripping the output.
At power-on or when the battery is replaced or recharged, and
the voltage at HTH exceeds the reference voltage, the output is
deasserted after a minimum delay of 140ms.
Typical Operation Circuit
PT0182(06/04)
Ver: 0
3
Preliminary Data Sheet
PT7M7479 Voltage Detector
with Adjustable Hysteresis
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Maximum Ratings
Storage Temperature ............................................................-65°C to +150°C
Ambient Temperature with Power Applied .......................... -40°C to +85°C
Supply Voltage to Ground Potential (Vcc to GND) ..............-0.3V to +7.0V
DC Input Voltage (All inputs except Vcc and GND)......-0.3V to VCC+0.3V
DC Output Current (All outputs) ..........................................................20mA
Power Dissipation .............................................................................. 320mW
(Depend on package)
Note:
Stresses greater than those listed under AXIMUM
RATINGS may cause permanent damage to the
device. This is a stress rating only and functional
operation of the device at these or any other conditions above those indicated in the operational sections of this specification is not implied. Exposure
to absolute maximum rating conditions for extended
periods may affect reliability.
DC Electrical Characteristics
(1.5V ≤VCC ≤5.5V; TA = +25C, bold values indicate –40°C ≤TA ≤+85°C; Unless noted)
Symbol
Description
ICC
Supply Current
VCC
Operating Voltage Range
ILTH, IHTH
Test Conditions
Min
RST,RST not asserted
TA= -40~85ºC
Typ
Max
Unit
1
2
µA
5.5
V
10
nA
1.2
Input Leakage Current
0.005
1.240
VREF
VOL
VOH
Reference Voltage
Output Low Voltage
Output High Voltage
PT7M7479HB/LB
1.215
1.265
PT7M7479HA/LA
1.228
1.252
RST asserted or RST not asserted,
ISINK = 1.6mA ,VCC ≥ 1.6V
RST asserted or RST not asserted,
ISINK = 100µA ,VCC ≥ 1.2V
RST not asserted or RST asserted,
ISINK = 500µA ,VCC ≥ 1.6V
RST not asserted or RST asserted,
ISINK = 50µA ,VCC ≥ 1.2V
PT0182(06/04)
0.3
V
0.4
0.8VCC
0.8VCC
V
V
Ver: 0
4
Preliminary Data Sheet
PT7M7479 Voltage Detector
with Adjustable Hysteresis
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AC Electrical Characteristics
VHTH
VBATT
VLTH
0V
tRST
VRST
tRST
tD
VOH
VOL
VOH
VRST
VOL
Note A: The PT7M7479 ignores very brief transients.
See " Applications Information " for details
(VCC = 1.5V to 5.5V TA= -40~85ºC, unless otherwise noted. Typical values are at TA = +25ºC)
Symbol
Description
Test Conditions
Min
140
tW
Reset Pulse Width
At VCC or SENSE
tD
Propagation Delay
VLTH = VREF (max) +100mV to
VREF(min) -100mV
PT0182(06/04)
Typ
100
Max
Unit
420
ms
µs
Ver: 0
5
Preliminary Data Sheet
PT7M7479 Voltage Detector
with Adjustable Hysteresis
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Mechanical Information
SOT23-5
1.90
0.35
0.80
1.50 2.50
1.70 3.10
0-10o
0.30
0.50
0.95
0.09
0.20
0.20
0.55
2.80
3.00
0.90
1.10
0.01
0.13
X.XX
X.XX
Note:
DENOTES DIMENSIONS
IN MILLIMETERS
1) Controlling dimensions in millimeters.
2) Ref: JDDEC TO-236AB
SOT-23 Package Top Marking Instruction
AA LJ
DATE CODE
YEAR & WORK WEEK
PART NO.
2 BIT CODE
(See Table 1)
Example: AALJ
Table 1
No.
PART NO.: PT7M7809L
DATE CODE: YEAR 2003 WW10
Part No.
Code
No.
Part No.
Code
1
PT7M7479HA
hu
3
PT7M7479LA
hw
2
PT7M7479HB
hv
4
PT7M7479LB
hx
PT0182(06/04)
Ver: 0
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Preliminary Data Sheet
PT7M7479 Voltage Detector
with Adjustable Hysteresis
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Notes
Pericom Technology Inc.
Email: support@pti.com.cn
Web Site: www.pti.com.cn, www.pti-ic.com
China:
No. 20 Building, 3/F, 481 Guiping Road, Shanghai, 200233, China
Tel: (86)-21-6485 0576
Fax: (86)-21-6485 2181
Asia Pacific:
Unit 1517, 15/F, Chevalier Commercial Centre, 8 Wang Hoi Rd, Kowloon Bay, Hongkong
Tel: (852)-2243 3660
Fax: (852)- 2243 3667
U.S.A.:
3545 North First Street, San Jose, California 95134, USA
Tel: (1)-408-435 0800
Fax: (1)-408-435 1100
Pericom Technology Incorporation reserves the right to make changes to its products or specifications at any time, without notice, in order to improve design or
performance and to supply the best possible product. Pericom Technology does not assume any responsibility for use of any circuitry described other than the
circuitry embodied in Pericom Technology product. The company makes no representations that circuitry described herein is free from patent infringement or other
rights, of Pericom Technology Incorporation.
PT0182(06/04)
Ver: 0
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