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| BQ24075T Datasheet, PDF (13/29 Pages) Texas Instruments – 1.5A USB-Friendly Li-Ion Battery Charger and Power-Path Management IC | |||
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www.ti.com
bq24075T
bq24079T
SLUS937 â DECEMBER 2009
POWER ON
When VIN exceeds the UVLO threshold, the bq2407xT powers up. While VIN is below VBAT + VIN(DT), the host
commands at the control inputs (CE, EN1 and EN2) are ignored. The Q1 FET connected between IN and OUT
pins is off, and the status outputs CHG and PGOOD are high impedance. The Q2 FET that connects BAT to
OUT is ON. (If SYSOFF is high, Q2 is off). During this mode, the VOUT(SC2) circuitry is active and monitors for
overload conditions on OUT.
Once VIN rises above VBAT + VIN(DT), PGOOD is driven low to indicate the valid power status and the CE, EN1,
and EN2 inputs are read. The device enters standby mode if (EN1 = EN2 = HI) or if an input overvoltage
condition occurs. In standby mode, Q1 is OFF and Q2 is ON so OUT is connected to the battery input. (If
SYSOFF is high, FET Q2 is off). During this mode, the VOUT(SC2) circuitry is active and monitors for overload
conditions on OUT.
When the input voltage at IN is within the valid range: VIN > UVLO AND VIN > VBAT + VIN(DT) AND VIN < VOVP, and
the EN1 and EN2 pins indicate that the USB suspend mode is not enabled [(EN1, EN2) â (HI, HI)] all internal
timers and other circuit blocks are activated. The device then checks for short-circuits at the ISET and ILIM pins.
If no short conditions exists, the device switches on the input FET Q1 with a 100mA current limit to checks for a
short circuit at OUT. When VOUT is above VSC, the FET Q1 switches to the current limit threshold set by EN1,
EN2 and RILIM and the device enters into the normal operation. During normal operation, the system is powered
by the input source (Q1 is regulating), and the device continuously monitors the status of CE, EN1 and EN2 as
well as the input voltage conditions.
/ PGOOD= Hi-Z
/CHG = Hi-Z
BATTFET ON
VUVLO <VIN <VOVP
No
and
VIN >V BAT +VIN (DT)
Yes
/ PGOOD= Low
Yes
EN1=EN2=1
No
Yes
ILIM or ISET short ?
No
Begin Startup
IIN (MAX ) 100mA
Yes
VOUT short?
No
Input Current
Limit set by EN1
and EN2
No
/CE = Low
Yes
Begin Charging
Figure 23. Startup Flow Diagram
Copyright © 2009, Texas Instruments Incorporated
Product Folder Link(s): bq24075T bq24079T
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