Diodes API9221 - Manual (Page 9)

API9221
CAR/WALL or USB SUPPLY INPUT LITHIUM BATTERY
CHARGER with OVP USB BYPASS and 10mA LDO
API9221
Document number: DS32204 Rev. 2 - 2
9 of 15
www.diodes.com
November 2011
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T
Functional Characteristics (cont.)
Charging from Adapter Power (VDC pin) (cont.)
The maximum charge current available may be otherwise
limited by the car/wall adapter current limit, by thermal
protection within the API9221, or by the r
DS(ON)
of the
FET in the VDC charging path. For example, if IVDC is
set to 1A, there is a voltage drop of 0.6V due the typical
r
DS(ON)
of 600m Ω at room temperature. Therefore, the
voltage at the VDC input must be at least 4.8V to charge
the battery to 4.2V in the minimum time.
The VDC input is safe from damage up to 28V.
Charging from USB Power (VUSB pin)
The battery can be charged at a current of up to 0.5A
from this pin. In this case the maximum available charge
current is set by an external resistor R
IUSB
connected
between the IUSB and GND pins. If VUSB is greater than
the power-on threshold voltage (VPO
R
) and less than the
over-voltage protection threshold (OVP
VUSB
), the battery
will begin to charge at a rate dependent on the battery
voltage.
The resistor R
IUSB
resistor determines the charge current
according to
IUSB
R
6820
IUSB
= Amp
For example, a resistor value of 22k Ω sets a charge
current of 0.31A.
The recommended IUSB setting is 46.5mA to 465mA.
The maximum charge current available may be otherwise
limited by the external USB current limit, or by thermal
protection within the API9221.
The R
DS(ON)
of the FET in the USB charging path is
typically 600m Ω at room temperature. At the IUSB limit of
465mA, there is a voltage drop of nearly 0.3V.
Therefore, the voltage at the VUSB input must be at least
4.5V to charge the battery to 4.2V in the minimum time.
The VUSB input is safe from damage up to 28V.
Trickle Charge
When the battery voltage is below the Preconditioning
Threshold, V
MIN
, the charger is in the Trickle Charge
state and the charge current is limited to 18% of the
available charge current set by R
IVDC
or R
IUSB
. If the
USB charge current is programmed to a value less than
the VDC trickle charge, then this value of the USB
current is used in trickle mode (no derating).
When the battery voltage reaches V
MIN
, the charge
current increases to 100% of the available charge
current.
End-of-Charge Current
During charging, as the battery voltage approaches the
regulated value of 4.2V, the charging current will begin to
decrease. Eventually the charging current settles to a
value just low enough to maintain the regulated voltage.
When the current becomes less than the End-of-Charge
threshold current, I
MIN,
the logic output CHG goes
HIGH. The threshold current is set by an external resistor
connected between the IMIN and GND pins. This is
independent of whether the VDC or VUSB input is valid.
The resistor at IMIN determines the EOC threshold
current according to
IMIN
MIN
R
550
I
=
Amp
For example, a resistor value of 10k Ω sets the EOC
threshold current to 55mA.
Accuracy
When the constant voltage phase has been reached, the
battery is charged to 4.2V ±1%. This is the maximum
error over the ambient temperature range from -40°C to
+85°C.
Fault Summary and Protection
Overvoltage protection: If VDC is greater than OVP
VDC
(6.9V), the VDC charging path is turned off until VDC falls
below OVP
VDC
- HOVP
VDC
, where HOVP
VDC
is the OVP
hysteresis. Similarly, if VUSB is greater than OVP
VUSB
(5.4V), the USB charging path is turned off until VUSB
falls below OVP
VUSB
– HOVP
VUSB
.
USB_BYP current limit: The USB_BYP load current is
limited to 400mA (nominally).
USB_BYP reverse blocking: If the voltage at USB_BYP
is greater than VUSB, the USB bypass path is turned off.
BAT reverse blocking: If the battery voltage is greater
than either VDC or VUSB, the relevant charge path is
turned off.
VDC_LDO reverse blocking: If the voltage at VDC_LDO
is greater than VDC, the linear regulator is turned off.
Thermal protection: When the junction temperature
reaches 125°C, a current foldback circuit is activated.
This effectively limits the power dissipation to a safe
level.