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PDF NCP345SNT1 Data sheet ( Hoja de datos )
| Número de pieza | NCP345SNT1 | |
| Descripción | Overvoltage Protection IC | |
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NCP345
Overvoltage Protection IC
The NCP345 overvoltage protection circuit (OVP) protects
sensitive electronic circuitry from overvoltage transients and power
supply faults when used in conjunction with an external P−channel
FET. The device is designed to sense an overvoltage condition and
quickly disconnect the input voltage supply from the load before any
damage can occur. The OVP consists of a precise voltage reference, a
comparator with hysteresis, control logic, and a MOSFET gate driver.
The OVP is designed on a robust BiCMOS process and is intended to
withstand voltage transients up to 30 V.
The device is optimized for applications that have an external
AC/DC adapter or car accessory charger to power the product and/or
recharge the internal batteries. The nominal overvoltage threshold is
6.85 V so it is suitable for single cell Li−Ion applications as well as 3/4
cell NiCD/NiMH applications.
Features
• Overvoltage Turn−Off Time of less than 1.0 msec
• Accurate Voltage Threshold of 6.85 V (nominal)
• Undervoltage Lockout Protection
• CNTRL Input Compatible with 1.8 V Logic Levels
• Pb−Free Package is Available
Typical Applications
• Cellular Phones
• Digital Cameras
• Portable Computers and PDAs
• Portable CD and other Consumer Electronics
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5
1
THIN SOT−23−5
SN SUFFIX
CASE 483
PIN CONNECTIONS &
MARKING DIAGRAM
OUT 1
5 VCC
GND 2
CNTRL 3
4 IN
Y = Year
W = Work Week
(Top View)
ORDERING INFORMATION
Device
Package
Shipping†
NCP345SNT1 SOT−23−5
NCP345SNT1G SOT−23−5
(Pb−Free)
3000 / Tape &
Reel
(7 inch Reel)
†For information on tape and reel specifications,
including part orientation and tape sizes, please
refer to our Tape and Reel Packaging Specifications
Brochure, BRD8011/D.
AC/DC Adapter or
Accessory Charger
P−CH
Schottky
Diode
VCC
IN Undervoltage
Lock Out
+
−
Logic
FET
Driver
OUT
+
C1 LOAD
Vref
NCP345
GND
CNTRL
Microprocessor port
Note: This device contains 89 active transistors
Figure 1. Simplified Application Diagram
© Semiconductor Components Industries, LLC, 2004
December, 2004 − Rev. 5
1
Publication Order Number:
NCP345/D
1 page  
NCP345
APPLICATION INFORMATION
AC/DC Adapter or
Accessory Charger
Zener
Diode
(optional)
IN
GND
P−CH
Schottky
Diode
VCC
Undervoltage
Lock Out
+
−
Logic
FET
Driver
Vref
NCP345
Zener
Diode
OUT (optional)
CNTRL
Microprocessor
port
+
C1 LOAD
Figure 8.
Introduction
In many electronic products, an external AC/DC wall
adapter is used to convert the AC line voltage into a
regulated DC voltage or a current limited source. Line
surges or faults in the adapter may result in overvoltage
events that can damage sensitive electronic components
within the product. This is becoming more critical as the
operating voltages of many integrated circuits have been
lowered due to advances in sub−micron silicon lithography.
In addition, portable products with removable battery packs
pose special problems since the pack can be removed at any
time. If the user removes a pack in the middle of charging,
a large transient voltage spike can occur which can damage
the product. Finally, damage can result if the user plugs in
the wrong adapter into the charging jack. The challenge of
the product designer is to improve the robustness of the
design and avoid situations where the product can be
damaged due to un−expected, but unfortunately, likely
events that will occur as the product is used.
Circuit Overview
To address these problems, the protection system above
has been developed consisting of the NCP345 Over Voltage
Protection IC and a P−channel MOSFET switch such as the
MGSF3441. The NCP345 monitors the input voltage and
will not turn on the MOSFET unless the input voltage is
within a safe operating window that has an upper limit of
7.05 V. A zener diode can be placed in parallel to the load to
provide for secondary protection during the brief time that
it takes for the NCP345 to detect the overvoltage fault and
disconnect the MOSFET. The decision to use this secondary
diode is a function of the charging currents expected, load
capacitance across the battery, and the desired protection
voltage by analyzing the dV/dT rise that occurs during the
brief time it takes to turn−off the MOSFET. For battery
powered applications, a low−forward voltage Schottky
diode such as the MBRM120LT3 can be placed in series
with the MOSFET to block the body diode of the MOSFET
and prevent shorting the battery out if the input is
accidentally shorted to ground. This provides additional
voltage margin at the load since there is a small forward drop
across this diode that reduces the voltage at the load.
When the protection circuit turns off the MOSFET, there
can be a sudden rise in the input voltage of the device. This
transient can be quite large depending on the impedance of
the supply and the current being drawn from the supply at the
time of an overvoltage event. This inductive spike can be
clamped with a zener diode from IN to ground. This diode
breakdown voltage should be well above the worst case
supply voltage provided from the AC/DC adapter or
Cigarette Lighter Adapter (CLA), since the zener is only
intended to clamp the transient. The NCP345 is designed so
that the IN and VCC pin can safely protect up to 25 V and
withstand transients to 30 V. Since these spikes can be very
narrow in duration, it is important to use a high bandwidth
probe and oscilloscope when prototyping the product to
verify the operation of the circuit under all the transient
conditions. A similar problem can result due to contact
bounce as the DC source is plugged into the product.
For portable products it is normal to have a capacitor to
ground in parallel with the battery. If the product has a
battery pack that is easily removable during charging, this
scenario should be analyzed. Under that situation, the
charging current will go into the capacitor and the voltage
may rise rapidly depending on the capacitor value, the
charging current and the power supply response time.
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