RT9526 Datasheet, PDF (9/14 Pages) Richtek Technology Corporation – Linear Single Cell Li-Ion Battery Charger with Input Over Voltage Protection

RT9526
Application Information
The RT9526 is a fully integrated low cost single cell Li-ion
battery charger operable in Constant Current (CC) mode
or Constant Voltage (CV) mode. The CC mode current is
set with the external resistor, R_ISET, and the CV mode
voltage is fixed at 4.2V. If the battery voltage is below a
typical 2.8V pre-charge threshold, the RT9526 charges
the battery with a trickle current until the battery voltage
rises above the pre-charge threshold. The RT9526 is
capable of being powered up from AC adapter and USB
(Universal Serial Bus) port inputs.
4.2V
I_{CHG_FAST}
2.8V
16.7 %
I_{CHG_FAST}
CHG_SB
Trickle
CC
CV
Charge
Voltage
Charge
Current
I_IMIN
CHG
Indication
Figure 1. Typical Charge Profile
75 %
I_{CHG_FAST}
Time
VIN Over Voltage Protection
The input voltage is monitored by the internal comparator.
The OVP threshold is set at 11V (typ.). When the input
voltage exceeds the threshold, the controller outputs a
logic signal to turn off the power P-MOSFET to prevent
high input voltage from damaging the electronics in the
handheld system. Nevertheless, an AC input voltage over
28V will still damage the RT9526. When the input over
voltage condition is removed, the controller will enable
the output again by running through soft-start.
Charger Enable Input
ENB is an active-low logic input to enable the charger.
Drive the ENB pin low or leave it floating to enable the
charger. This pin has a 200kΩ internal pull down resistor.
So when left floating, the input is equivalent to logic-low.
Drive this pin high to disable the charger.
Battery Charge Profile
The RT9526 charges a Li-ion battery under Constant
Current (CC) mode or Constant Voltage (CV) mode. The
constant current of ISET is set via the external resistor,
R_ISET, and the constant voltage is fixed at 4.2V. If the battery
voltage is below a typical 2.8V pre-charge threshold, the
RT9526 charges the battery with a trickle current until
the battery voltage rises above the pre-charge threshold.
When the battery voltage reaches 4.2V, the charger enters
CV mode and regulates the battery voltage at 4.2V to
fully charge the battery without the risk of over charge.
a. Battery Pre-Charge Current
During a charge cycle, if the battery voltage is below the
pre-charge threshold, the RT9526 applies a pre-charge
mode to the battery. This feature revives deeply discharged
cells and protects battery life. The internally determined
pre-charge rate of the RT9526 is 16.7% of the constant
charge current.
b. Battery Fast-Charge Current (CC Mode)
The RT9526 offers ISET pin to determine the fast-charge
current via an external resistor, R_ISET, connected between
ISET and GND. The fast-charge current can be calculated
by the following equation :
I_{CHG_FAST}
= K_ISET
x
V_ISET
R_ISET
(mA)
K_SET = 3640; V_SET = 1.21 (typ.)
c. Battery Voltage Regulation (CV Mode)
The battery voltage regulation feedback is through the
BATT pin. The RT9526 monitors the battery voltage
between the BATT and GND pins. When battery voltage is
close to battery regulation voltage threshold, the voltage
regulation phase begins and the charging current begins
to taper down. When battery voltage is over battery
regulation voltage threshold and charge mode stops, the
RT9526 still monitors the battery voltage. Charge current
is resumed when the battery voltage falls under battery
regulation voltage threshold.
Sleep Mode
The RT9526 enters sleep mode if both AC and USB are
removed from the input. This feature prevents draining the
battery during the absence of input supply.
DS9526-01 April 2011
www.richtek.com
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