BQ25050 Datasheet, PDF (21/28 Pages) Texas Instruments – 1A, Single-Input, Single Cell Li-Ion Battery Charger with 50-mA LDO, External Power Path

bq25050
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APPLICATION INFORMATION
SLUSA33 – MARCH 2010
Selection of Input/ Output Capacitors
In most applications, all that is needed is a high-frequency decoupling capacitor on the input power pin. For
normal charging applications, a 0.1µF ceramic capacitor, placed in close proximity to the IN pin and GND pad
works best. In some applications, depending on the power supply characteristics and cable length, it may be
necessary to increase the input filter capacitor to avoid exceeding the OVP voltage threshold during adapter hot
plug events where the ringing exceeds the deglitch time.
The charger in the bq25050 requires a capacitor from OUT to GND for loop stability. Connect a 1µF ceramic
capacitor from OUT to GND close to the pins for best results. More output capacitance may be required to
minimize the output droop during large load transients. Connect a 0.1µF ceramic capacitor from BAT to GND to
eliminate the potential ESD strike.
The LDO also requires an output capacitor for loop stability. Connect a 0.1µF ceramic capacitor from LDO to
GND close to the pins. For improved transient response, this capacitor may be increased.
bq25050 Charger Design Example
The following sections provide an example for determining the component values for use with the bq25050.
Requirements Refer to Figure 1 and Figure 2 for Schematics of the Design Example
• Supply voltage = 4.35~10.2V
• Fast charge current is set by CTRL - pin 7
• Input current monitoring output - pin 2
• Set 0°C~45°C operating range
Calculations
Program the Fast Charge Current (CTRL): Programming the different input currents, BGATE option,
temperature operating range, and VIN-DPM is done by pulsing the CTRL input. See table 2 for details. If, at any
time, the CTRL input is held high for more than 2ms, the IC is disabled. After CTRL is pulled low for more than
2ms, the charger resumes. See Figure 26 for details.
Program the input current monitoring output (IMON): Connect a resistor from IMON to VSS to monitor the
input current. The voltage of IMON pin is determined by:
V_IMON = K_IMON × R_IMON × I_CHG
The maximum IMON pin voltage is typically 1.2V. If the V_IMON is programmed to be higher than V_IMON(MAX), the
V_IMON will be clamped on V_IMON(MAX). But, I_CHG is controlled by the CTRL pin separately and is not affected by
V_IMON.
Set charger operating temperature range (TS): The operating range is 0°C to 45°C by a default NTC
thermistor NCP15WB473F (47kΩ Thermistor, b=4050). 12 qualified CTRL pulses can set V_{HOT_60} as TS hot
threshold and set 0°C to 60°C as the operating range. The following conditions will reset temperature operating
range back to 0°C to 45°C.
• Input voltage is lower than UVLO
• The CTRL input is held high for more than 2ms
In battery discharge mode, the TS function is disabled if the CHG voltage falls below logic low.
External FET Controller (BGATE): On Figure 1, BGATE drives an external P-channel FET that connects the
battery to the system output. When power is first applied to either V_BAT or V_IN, the device sources a typical 50µA
small current out of BGATE and monitors the voltage. If BGATE voltage is higher than logic high in first 1ms and
stays high for at least 2ms, the external power path control feature is enabled and V_LOWV is set to 2.9V. The OUT
pin maintains voltage at V_OUT(REG).
In Figure 2, BGATE is connected to Vss. The external power path control feature is disabled and V_LOWV is set to
2.5V. The OUT pin shorts to BAT.
Status Indicators (CHG): The CHG pin is open drain output. If used, CHG pin should be pulled up via a resistor
and possibly a LED to a power source. If monitored by a host, the host pull-up power source should be used.
Copyright © 2010, Texas Instruments Incorporated
Product Folder Link(s): bq25050
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