bq24030, bq24031, bq24032,
bq24032A, bq24035, bq24038, bq24039
www.ti.com
SLUS618C–AUGUST 2004–REVISED JUNE 2005
V
K
(SET)
(PRECHG)
I
+
O (PRECHG)
R
SET
(3)
The bqTINY-III activates a safety timer, t(PRECHG), during the conditioning phase. If V(LOWV) threshold is not
reached within the timer period, the bqTINY-III turns off the charger and enunciates FAULT on the STAT1 and
STAT2 pins. The timeout is extended if the charge current is reduced by DPPM. See the Timer Fault Recovery
section for additional details.
Battery Charge Current
The bqTINY-III offers on-chip current regulation with programmable set point. The resistor connected between
the ISET1 and VSS, RSET, determines the charge level. The charge level may be reduced to give the system
priority on input current (see DPPM). The V(SET) and K(SET) parameters are specified in the specifications table.
V
K
(SET)
(SET)
I
+
O (OUT)
R
SET
(4)
When powered from a USB port, the input current available (0.1 A/0.5 A) is typically less than the programmed
(ISET1) charging current, and therefore, the DPPM feature attempts to keep the output from being pulled down
by reducing the charging current.
For the bq24032/2A/8 the charge level, during AC operation only (PSEL = High), can be changed by a factor of 2
by setting the ISET2 pin high (full charge) or low (half charge). The voltage on the ISET1 pin, VSET1, is divided
by 2 when in the half constant current charge mode. Note that with PSEL low, the ISET2 pin controls only the
0.1 A/0.5 A USB current level.
See the section titled Power-Path Management for additional details.
Battery Voltage Regulation
The voltage regulation feedback is through the BAT pin. This input is tied directly to the positive side of the
battery pack. The bqTINY-III monitors the battery-pack voltage between the BAT and VSS pins. When the
battery voltage rises to the VO(REG) threshold, the voltage regulation phase begins and the charging current
begins to taper down.
If the battery is absent, the BAT pin cycles between charge done (VO(REG)) and charging (battery refresh
threshold, ~4.1 V). See Figure 11.
See Figure 12 for power up by battery insertion.
As a safety backup, the bqTINY-III also monitors the charge time in the charge mode. If charge is not terminated
within this time period, t(CHG), the bqTINY-III turns off the charger and enunciates FAULT on the STAT1 and
STAT2 pins. See the DPPM operation under Case 1 for information on extending the safety timer during DPPM
operation. See theTimer Fault Recovery section for additional details.
Power Handoff
The design goal of the IC is to keep the system powered at all times (OUT pin), first by either input, AC or USB,
priority chosen by PSEL (PSEL feature set high internally on bq24039), and lastly by the battery. The input
power source is only considered present if its power-good status is low. There is a break-before-make switching
action when switching between AC to USB or USB to AC, for tSW-AC/USB, where the system capacitance should
hold up the system voltage. Note that the transfer of power occurs when the sources power-good pin goes high
(open-drain output high = power not present), which is when the input source drops to the battery's voltage. If the
battery is below a useable voltage, the system may reset. Typically, prior to losing the input power, the battery
would have some useable capacity, and a system reset would be avoided. If the battery was dead or missing,
the system would lose power unless the PSEL pin was used to transfer power prior to shutdown.
If this is a concern, there is a simple external solution. Externally toggling the PSEL (bq24030/1/2/2A/5/8) pin
immediately starts the power-transfer process (does not wait for input to drop to the battery's voltage). This can
22
TI [ TEXAS INSTRUMENTS ]
