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TC3827-4.2VUA Datasheet(PDF) 3 Page - Microchip Technology |
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TC3827-4.2VUA Datasheet(HTML) 3 Page - Microchip Technology |
3 / 10 page 3 Lithium-Ion Battery Charger TC3827 TC3827-2 12/12/00 © 2001 Microchip Technology Inc. DS21558A Pin No. 8-Pin MSOP Symbol Type Description 1 SHDN Signal Input Shutdown Input 2 GND Power System Ground 3 MODE Signal Output Charge Mode Indicator 4IMON Voltage Output Buffered Copy of Current Sense Resistor Drop 5VOUT Voltage Input Charger DC Output Voltage Sense 6VDRV Signal Output Gate Drive to External MOSFET 7VSNS Signal Input Current Sense Voltage Input 8VIN Power Charger DC Input Voltage PIN DESCRIPTION FUNCTIONAL DESCRIPTION The TC3827 controller only requires a P-channel power MOSFET and two small capacitors to perform as an inex- pensive Li-Ion battery charger. The TC3827 controller drives an external PMOS to provide a regulated output current to charge the battery. Initially, current limited charging occurs until a pre-specified battery voltage is measured at the VOUT pin. It then switches to constant-voltage mode. During constant-voltage mode the TC3827 works like a linear regulator, holding the output voltage within the specified accuracy. The charger output is sensed at the VOUT pin. The charging current follows the foldback characteristic as shown in Figure 2. The sense resistor sets the maximum charging current, IMAX. The voltage drop across the current sense resistor is sensed at the VSNS input. An amplified copy of this sense voltage is provided as output on the current monitor pin (IMON). When the battery is deeply discharged to a minimum voltage level, or if the battery is shorted, the current sense circuit folds back the charge current to limit the power dissipation of the PMOS. Both the VIN and VOUT pins I/O DESCRIPTION SHDN: When SHDN is low, VDRV is pulled high to VIN and the charge is interrupted. GND: Connect to the battery’s negative terminal. See Layout Guidelines for information on system grounding. VOUT: Battery positive terminal and charger regulated output voltage.This pin is connected to the external PMOS drain and directly to the load for optimal regulation. VOUT pin draws typically 1µA from the battery when VIN power is removed. Requires a Bypass capacitor. MODE: Charge Status Indicator. Mode is an open-drain, N-channel MOSFET capable of sinking 20mA for an LED status indication of charger in current limited mode. LED is off in current-voltage mode. VDRV: Gate drive output for the external PMOS pass device. IMON : Battery Charge current profile. This output is an amplified copy of the voltage drop across the current sense resistor. It can be used as input to an A/D converter to provide the controller with information about the charge current profile. VIN: Charger power supply input (+6V absolute max.). Bypass to GND with a capacitor. VSNS: Battery charge current sense voltage feedback. This voltage is developed across a small value precision resistor that is in series with the battery. of the IC need a suitable bypass capacitor. The TC3827 also has a logic-level shutdown input, SHDN, which may be connected to the input voltage to enable the IC. Pulling it “low” or to ground will disable the PMOS drive (VDRV pulled up to VIN voltage). Also, a charger mode pin (MODE) is provided to drive an optional LED for a visual indication of current limited mode operation. LED will be turned off in constant voltage mode operation. |
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