AT1457
Preliminary Product Information
1-Cell Lithium-Ion And Lithium-Polymer
Charge Management IC
4.Reverse Current Blocking Diode
(A) Transistor Circuit Application
When using the AT1457 with a PNP Transistor, a reverse-blocking diode is not
required because there is no current path from BAT to VIN. However, it is
advisable to still place a diode to the circuit. In the event where the input supply is
interrupted or removed during the constant current or constant voltage phases, the
battery under charge will discharge through the circuit pass transistor rendering it
impossible to turn off. If the circuit is unable to turn off, the reverse leakage will
discharge the battery. A Blocking diode will prevent this undesirable effect.
(B) MOSFET Circuit Application
An reverse blocking diode is required for the circuit show in Figure 3. The blocking
diode gives the system protection from a shorted input. It also prevent the leakage
current of battery when the input power is interrupted or removed.
5.Input Capacitor
It is good design practice to place a decoupling capacitor between VCC and VSS
pins. An input capacitor in the range of 0.1µF to 10µF is recommended. A larger
input capacitor in application will minimize switching or power bounce effects
when the power supply is “hot plugged” in.
6.Input Capacitor
The AT1457 does not need an output capacitor for stability of the device itself,
However, a capacitor connected between BAT and VSS will control the output
voltage when the AT1457 is powered up when no battery is connected. If a high
impedance load is placed across the BAT pin to VSS, the AT1457 can become
unstable. Such a case is possible with aging Li-Ion battery cells. As cells age
through repeated charge and discharge cycles, the internal impedance can rise over
time. A 10µF or larger output capacitor will compensate for the adverse effects of a
high impedance load and assure device stability over all operating conditions.
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10/3/2006 REV:1.2
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