Datasheet

( )
INDPM DPM
DPM
10k V V
RTOP
V
W ´ -
=
bq24278
www.ti.com SLUSB04 –JUNE 2012
Figure 6. bq24278 V
IN-DPM
The VINDPM 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 Equation 7:
(7)
Where V
INDPM
is the desired V
INDPM
threshold and V
DPM
is the regulation threshold specified in the Electrical
Characteristics table.
Bad Source Detection
When a source is connected to IN, the bq24278 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 (70mA) for
32ms. If the source is valid after the 32ms (V
BADSOURCE
< V
IN
< 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 2s and then retries. The detection circuits retries continuously until a valid source is detected after the
detection time. If during normal operation the source falls to V
BAD_SOURCE
, the bq24278 turns off the PWM
converter, turns the battery FET on and runs the bad source detection. Once a good source is detected, the
device returns to normal operation.
Input Over-Voltage Protection
The bq24278 provides over-voltage protection on the input that protects downstream circuitry. The built-in input
over-voltage protection to protect the device and other components against damage from overvoltage on the
input supply (Voltage from V
IN
to PGND). When V
IN
> V
OVP
, the bq24278 turns off the PWM converter, suspends
the charging cycle and turns the battery FET on. Once the OVP fault is removed, the device returns to the
operation it was in prior to the OVP fault.
Status Indicators (CHG, PG)
The bq24278 contains two open-drain outputs that signal its status. The PG output indicates that a valid input
source is connected to IN. PG is low when (V
BAT
+V
SLP
) < V
IN
< V
OVP
. When there is no supply connected to the
input within this range, PG is high impedance. Table 1 illustrates the PG behavior under different conditions.
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