BQ24314C Datasheet, PDF (13/26 Pages) Texas Instruments – Li+ Charger Front-End Protection IC

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bq24314C
SLUSAV3A – AUGUST 2012 – REVISED JULY 2015
Application Information (continued)
If V_OUT > UVLO + 0.7 V, FET Q1 is turned on, and the reverse current does not flow through the diode but
through Q1. Q1 will then remain 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, 1.5 A. It should be noted that
there is no overcurrent protection in this direction.
8.2 Typical Application
The typical values for an application are V_OVP = 6.8 V, I_OCP = 1000 mA, BV_OVP = 4.45 V
AC Adapter
VDC
GND
1 ^IN
C_IN
1 mF
OUT ₈
1 mF
bq24314C
C_OUT
bq24080
Charger IC
VBAT ₆
R_BAT
100 kW
V_PU
7
R_ILM
FAULT ₄
CE ₅
2
R_PU 47 kW
47 kW
R_FAULT
47 kW
R_CE
SYSTEM
Host
Controller
Terminal numbers shown are for the 2 × 2 DSG package.
Figure 12. Typical Application Circuit
8.2.1 Design Requirements
For this design example, use the parameters listed in Table 1.
Table 1. Design Parameters
DESIGN PARAMETER
Supply Voltage
INILIM
EXAMPLE VALUE
5V
1A
8.2.2 Detailed Design Procedure
8.2.2.1 Selection of R_BAT
It is strongly recommended that the battery not be tied directly to the VBAT pin of the device, as under some
failure modes of the IC, the voltage at the IN pin may appear on the VBAT pin. This voltage can be as high as 30
V, and applying 30 V to the battery in case of the failure of the bq24314C device can be hazardous. Connecting
the VBAT pin through R_BAT prevents a large current from flowing into the battery in case of a failure of the
device. In the interests of safety, R_BAT should have a very high value. The problem with a large R_BAT is that the
voltage drop across this resistor because of the VBAT bias current I_VBAT causes an error in the BV_OVP threshold.
This error is over and above the tolerance on the nominal 4.45 V BV_OVP threshold.
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