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1
Introduction
2
Considerations When Testing and Using bq2403x ICs
Introduction
The bqTiny-III powers the system while independently charging the battery. This feature reduces the
charge and discharge cycles on the battery, allows for proper charge termination, and allows the system
to run with an absent or defective battery pack. This feature also allows for the system to instantaneously
turn on from an external power source even when using a deeply discharged battery pack.
The bqTiny-III automatically selects the USB port or the ac adapter as the power source for the system. In
the USB configuration, the host can select from the two preset input maximum rates of 100 mA and 500
mA. The bqTiny-III dynamically adjusts the USB charge rate based on the system load to stay within the
100-mA or 500-mA maximum rates. The AC pin can be programmed to perform like a USB input by
pulling the PSEL pin low. An external resistor, RSET1, sets the magnitude of the charge current. If the
charge current exceeds the available input current, the voltage on the OUT pin drops to the DPPM
OUT
threshold or the battery voltage, which ever is higher. The charging current is reduced to what current is
available (I
BAT
= I
IN
–I
OUT
).
The bqTiny-III charges the battery in three phases: conditioning, constant current, and constant voltage.
Charge is terminated based on minimum current. A resistor-programmable charge timer provides a
backup safety for charge termination. The bqTiny-III automatically re-starts the charge if the battery
voltage falls below an internal threshold. The bqTiny-III automatically enters sleep mode when both
supplies are removed (a drop to the battery voltage).
Consider the following noteworthy items while testing and using the bq2403x ICs.
There are three ICs (bq24030/1/2/5) to select from. The significant difference is the OUT pin voltage. The
bq24030/1 has a LDO 6-V regulator connected the OUT pin. The intent on this charger is to provide a
solution for using an inexpensive unregulated adaptor to power the charger. When unloaded, a 5-VDC
adapter peak charges to ~8 V, but when loaded it quickly drops closer to 5 V. Since this is a linear
regulator/charger, the higher the input voltage the lower the current level has to be to not exceed the
power rating of the IC. The bq24032 has a LDO 4.4-V regulator connected to the OUT pin. The bq24035
shuts down if the input exceeds ~6.4 VDC.
The three potential sources to power the system (V
OUT
) are: AC (AC-to-DC adapter), USB port, and
battery. The IC is designed to power the system continuously. The battery, in most cases, is the last line
of backup. If the AC or USB inputs are not available (or disabled), the battery connects to the system.
In thermal regulation condition (T
J
=125°C—not a first-choice design mode of operation), the charge
current is reduced to the battery, and the system still gets its power from the input. The battery
supplement is still available in thermal regulation if the V
OUT
falls to V
BAT
. In thermal cutoff (~155°C), the
input sources are disconnected, but the internal battery FET connects the battery to V
OUT
.
The battery FET only opens (when needed) if a short on the V
OUT
pulls more than 4 A of current, or any
condition has V
OUT
less than 1 Vdc (considered a short-circuit condition). In the short-circuit condition are
two types of pullups: a 500-
Ω
resistor from each input to V
OUT
and a 10-mA current source from the
battery to the V
OUT
. The system load has to be reduced (>200
Ω
) on the output to allow V
OUT
to rise above
1 Vdc. If the voltage on the DPPM pin is held below 1 V, then the short-circuit feature is disabled.
Therefore, placing a small capacitor (~1000 pF) across the DPPM resistor delays the short-circuit
protection on input powerup by a few microseconds. Typically, the system does not have much of a load
below 1 V; so, powering up during a potential short-circuit condition usually is not a problem. V
OUT
is
always powered if there is any source voltage; so, dropping below 1 V is not a typical mode.
Another feature that protects system integrity is dynamic power path management (DPPM). The voltage
on the DPPM pin (DPPM
IN
) times a scaling factor of ~1.15 is the DPPM
OUT
voltage. The DPPM
OUT
voltage
is the critical voltage, determined by the designer, where battery charging current is reduced to keep the
system voltage (V
OUT
) from further decay. A special feature to keep in mind is that when in DPPM mode
the internal oscillator timer is slowed proportionally to how much the programmed charger current is
reduced. This allows the timers (safety and others) to be appropriately adjusted during operation.
Therefore, when performing any test where time is measured, keep in mind this adjustment factor.
2
bq2403x (bqTiny-III™) 1.5-A Single-Chip Li-Ion
SLUU207A – October 2004 – Revised January 2007
and Li-Pol Charge Management IC EVM