YB1880 Datasheet, PDF (9/10 Pages) YOBON TECHNOLOGIES,INC. – Standalone Linear Lithium Battery Charger

YB1880
Standalone Linear Lithium Battery Charger
Application Hints
Stability Considerations
The constant-voltage mode feedback loop is stable without an output capacitor provided a battery is
connected to the charger output. With no battery present, an output capacitor is recommended to reduce
ripple voltage. When using high value, low ESR ceramic capacitors, it is recommended to add a 1Ω resistor in
series with the capacitor. No series resistor is needed if tantalum capacitors are used. In constant-current
mode, the PROG pin is in the feedback loop, not the battery. The constant-current mode stability is affected
by the impedance at the PROG pin. With no additional capacitance on the PROG pin, the charger is stable
with program resistor values as high as 20k. However, additional capacitance on this node reduces the
maximum allowed program resistor. The pole frequency at the PROG pin should be kept above 100kHz.
VCC Bypass Capacitor
Many types of capacitors can be used for input bypassing, however, caution must be exercised when using
multilayer ceramic capacitors. Because of the self-resonant and high Q characteristics of some types of
ceramic capacitors, high voltage transients can be generated under some start-up conditions, such as
connecting the charger input to a live power source. Adding a 1.5Ω resistor in series with a ceramic capacitor
will minimize start-up voltage transients.
Power Dissipation
The conditions that cause the YB1880 to reduce charge current through thermal feedback can be
approximated by considering the power dissipated in the IC. Nearly all of this power dissipation is generated
by the internal MOSFET—this is calculated to be approximately:
The approximate ambient temperature at which the thermal feedback begins to protect the IC is:
Thermal Considerations
Because of the small size of the thin SOT23 package, it is very important to use a good thermal PC board
layout to maximize the available charge current. The thermal path for the heat generated by the IC is from the
die to the copper lead frame, through the package lead, (especially the ground lead) to the PC board copper.
The PC board copper is the heat sink. The footprint copper pads should be as wide as possible and expand
out to larger copper areas to spread and dissipate the heat to the surrounding ambient. Other heat sources on
the board, not related to the charger, must also be considered when designing a PC board layout because
they will affect overall temperature rise and the maximum charge current.
YB1880 Rev.1.0
www.yobon.com.tw
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