BQ24315 Datasheet, PDF (13/20 Pages) Texas Instruments – OVERVOLTAGE AND OVERCURRENT PROTECTION IC AND Li+ CHARGER FRONT-END PROTECTION IC

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AC Adapter
IN OUT
bq24315
Accessory
DIS
power supply
Charger
EN
Battery
pack
bq24315
SLUS817 – MARCH 2008
e.g.
cellphone
to rest of
system
Figure 22. Charging - The Red Arrows Show the Direction of Current Flow
IN OUT
bq24315
Accessory
EN
power supply
Charger
DIS
Battery
pack
e.g.
cellphone
to rest of
system
Figure 23. Powering an Accessory - The Red Arrows Show the Direction of Current Flow
In the second case, when power is being delivered to an accessory, the bq24315 device is required to support
current flow from the OUT pin to the IN pin.
If V_OUT > UVLO + 0.7V, FET Q1 is turned on, and the reverse current does not flow through the diode but
through Q1. Q1 remains ON as long as V_OUT > UVLO – V_hys(UVLO) + R_DS(on) × I_(ACCESSORY). Within this voltage
range, the reverse current capability is the same as the forward capability, 1.5A. It should be noted that there is
no overcurrent protection in this direction.
PCB Layout Guidelines:
• This device is a protection device, and is meant to protect down-stream circuitry from hazardous voltages.
Potentially, high voltages may be applied to this IC. It has to be ensured that the edge-to-edge clearances of
PCB traces satisfy the design rules for high voltages.
• The device uses SON packages with a PowerPAD™. For good thermal performance, the PowerPAD should
be thermally coupled with the PCB ground plane. In most applications, this will require a copper pad directly
under the IC. This copper pad should be connected to the ground plane with an array of thermal vias.
• C_IN and C_OUT should be located close to the IC. Other components like R_(ILIM) and R_BAT should also be
located close to the IC.
Copyright © 2008, Texas Instruments Incorporated
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