BQ25040 Datasheet, PDF (16/25 Pages) Texas Instruments – 1.1A, Single-Input, Single Cell Li-Ion Battery Charger With 50mA LDO and 2.3A Production Test Support

bq25040
SLUS910B – MARCH 2009 – REVISED MARCH 2009 ...................................................................................................................................................... www.ti.com
V_ISET
V_IN
500mV/div
2V/div
200mA/div
I_OUT
USB500
Time - 1ms/div
Figure 24. V_IN-DPM Protects from Crashing Poor Input Sources
50 mA LDO (LDO)
The LDO output of the bq25040 is a low dropout linear regulator (LDO) that supplies up to 50mA while regulating
to V_LDO. The LDO is active whenever the input voltage is between UVLO and V_OVP. It is not affected by the
EN/SET input. The LDO output is used to power circuitry such as USB transceivers in dead battery conditions.
This allows the user to operate the product immediately after plugging the adapter in, instead of waiting for the
battery to charge to useable levels. Note that the LDO current is not monitored by the input current limit. The
LDO current is limited separately and is in addition to the input current limit.
Charge Done Indicator (CHG)
The bq25040 contains an open drain CHG output that indicates when a charge cycle is complete. When charging
a battery in precharge, fastcharge or CV mode, the CHG output is pulled to VSS. Once the BAT output reaches
regulation and the charge current falls below the termination threshold, CHG goes high impedance to signal the
battery is fully charged. The CHG output remains high during subsequent battery refresh charges. Connect CHG
to the required logic level voltage through a 1kΩ to 100kΩ resistor to use the signal with a microprocessor.
Additionally, CHG may be used to drive an LED for a visual charging status signal. I_CHG must be below 15mA.
CHG may be pulled up to any voltage rail less than the maximum rating on the CHG output. Many LED
applications choose to pull up CHG to the battery voltage. This is acceptable; however, note that at low battery
conditions, the LED may appear dim. Another option is to pull up CHG to the LDO output. This is also
acceptable; however, note that the LDO current is not limited by the input current limit and the additional current
may cause the bq25040 input current to exceed the maximum USB100 specification.
Power Good (PG)
The bq25040 contains a PG signal that indicates when a valid input source is connected. The PG output goes
low when an input source between (V_BAT + 80mV) and V_OVP is connected. Additionally, the input source must be
greater than the UVLO voltage threshold. See Table 2 for the nominal PG deglitches under different conditions.
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