Datasheet

ACSET
DPM
AC
V
I =
20 R´
ISET2
PRECHARGE
SR
V
I =
100 R´
ISET2
TERM
SR
V
I =
100 R´
CHARGE TTC TTC
t = C K´
bq24616
www.ti.com SLUSA49B –APRIL 2010– REVISED OCTOBER 2011
Input Adapter Current Regulation
The total input from an ac adapter or other dc source is a function of the system supply current and the battery
charging current. System current normally fluctuates as portions of the systems are powered up or down. Without
dynamic power management (DPM), the source must be able to supply the maximum system current and the
maximum charger input current simultaneously. By using DPM, the battery charger reduces the charging current
when the input current exceeds the input current limit set by ACSET. The current capability of the ac adaptor can
be lowered, reducing system cost.
Similar to setting battery regulation current, adaptor current is sensed by resistor R
AC
connected between ACP
and ACN. Its maximum value is set by ACSET using Equation 3:
(3)
V
ACSET
, the input voltage range of ACSET, is between 0 and 2 V. The ACP and ACN pins are used to sense
voltage across R
AC
with a default value of 10 mΩ; however, resistors of other values can also be used. A larger
sense resistor gives a larger sense voltage and a higher regulation accuracy, but at the expense of higher
conduction loss.
Precharge
On power up, if the battery voltage is below the V
LOWV
threshold, the bq24616 applies the precharge current to
the battery. This feature is intended to revive deeply discharged cells. If the V
LOWV
threshold is not reached within
30 minutes of initiating precharge, the charger turns off and a FAULT is indicated on the status pins.
The precharge current (I
PRECHARGE
) is determined by the voltage on the ISET2 pin (V
ISET2
) according to
Equation 4.
(4)
Charge Termination, Recharge, and Safety Timer
The bq24616 monitors the charging current during the voltage regulation phase. When V
TTC
is valid, termination
is detected while the voltage on the VFB pin is higher than the V
RECH
threshold AND the charge current is less
than the I
TERM
threshold, as calculated in Equation 5:
(5)
V
ISET2
, the input voltage of ISET2, is between 0 and 2 V. The minimum precharge/termination current is clamped
to be around 125 mA with default 10-mΩ sensing resistor. As a safety backup, the bq24616 also provides a
programmable charge timer. The charge time is programmed by the capacitor connected between the TTC pin
and GND, and is given by Equation 6
(6)
where C
TTC
(range from 0.01 µF to 0.11 µF to give 1-h to 10-h safety time) is the capacitor connected from the
TTC pin to GND, and K
TTC
is the constant multiplier (5.6 min/nF).
A new charge cycle is initiated and the fast-charge safety timer is reset when one of the following conditions
occurs:
• The battery voltage falls below the recharge threshold.
• A power-on-reset (POR) event occurs.
• CE is toggled.
The TTC pin may be taken LOW to disable termination and to disable the safety timer. If TTC is pulled to VREF,
the bq24616 continues to allow termination but disables the safety timer. TTC taken low resets the safety timer.
When ACOV, VCCLOWV, and SLEEP mode resume normal, the safety timer also is reset.
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