BQ24165 Datasheet, PDF (21/35 Pages) Texas Instruments – 2.5A, Dual-Input, Single Cell Switch Mode Li-Ion Battery Charger with Power Path

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bq24165
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SLUSAP4A – DECEMBER 2011 – REVISED MARCH 2012
Input Voltage Based DPM
During normal charging process, if the input power source is not able to support the programmed or default
charging current, the supply voltage decreases. Once the supply drops to V_{IN_DPM} (set by IUSB_ for USB input or
VDPM for IN input), the input current limit is reduced down to prevent the further drop of the supply. This feature
ensures IC compatibility with adapters with different current capabilities without a hardware change. Figure 24
shows the V_IN-DPM behavior to a current limited source. In this figure the input source has a 750mA current limit
and the charging is set to 750mA. The SYS load is then increased to 1.2A.
V_IN
5 V Adapter
rated for 750 mA
I_IN
V_SYS
I_BAT
I_SYS
Figure 24. bq2416x V_IN-DPM
The V_IN-DPM threshold for the IN input is set using a resistor divider with VDPM connected to the center tap.
Select 10kΩ for the bottom resistor. The top resistor is selected using the following equation:
RTOP = ^{10 kΩ ´ (VINDPM - VDPM )}
V_DPM
(7)
Where V_INDPM is the desired V_INDPM threshold and V_DPM is the regulation threshold specified in the Electrical
Characteristics table. Additionally, a small capictance (<0.01µF) may be added to VDPM if the layout is not ideal
and significant noise exists on the VDPM line.
Bad Source Detection
When a source is connected to IN or USB, the bq2416x runs a Bad Source Detection procedure to determine if
the source is strong enough to provide some current to charge the battery. A current sink is turned on (30mA for
USB input, 75mA for the IN input) for 32ms. If the source is valid after the 32ms (V_BADSOURCE < V_SUPPLY < V_OVP),
the buck converter starts up and normal operation continues. If the supply voltage falls below V_{BAD_SOURCE} during
the detection, the current sink shuts off for two seconds and then retries. The detection circuit retries
continuously until either a new source is connected to the other input or a valid source is detected after the
detection time. If during normal operation the source falls to V_{BAD_SOURCE}, the bq2416x turns off the PWM
converter, turns the battery FET on. Once a good source is detected, the device returns to normal operation.
If two supplies are connected, the IN supply is checked first. If the supply detection fails once, the device
switches to USB for two seconds and then retries IN. This allows the supply to settle if the connection was jittery
or the supply ramp was too slow to pass detection. If the supply fails the detection twice, it is locked out and the
USB supply is used. Once the bad supply is locked out, it remains locked out until the supply voltage falls below
UVLO. This prevents continuously switching between a weak supply and a good supply.
Copyright © 2011–2012, Texas Instruments Incorporated
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