AME2056 Datasheet, PDF (15/26 Pages) Analog Microelectronics – 1A Single Cell Li-ion

AME
AME2056
1A Single Cell Li-ion
Battery Linear Charger
Power Dissipation
AME2056 has thermal feedback protection to reduce the charging current in overload condition, so the power dissipa-
tion is required to consider. The power dissipation definition is:
P_D = (V_CC −V_BAT ) × I _BAT
Where P_D is power dissipated, V_CC is the input supply current, V_BAT is the battery voltage and I_BAT is the charge current.
AME2056 will automatically reduce the charging current to maintain the die temperature under 145^oC approximately,
so it is not necessary to check maximum power dissipation. The ambient temperature of thermal feedback protection is:
( ) T_A = 145^o C − P_D × θ _JA = 145^o C − V_CC − V_BA × θ _JA
For example: AME2056 operating from a 5V power providing 0.8A to a 3.75V Li-Ion battery. The maximum ambient
temperature which the AME2056 operates in 0.8A condition can be calculated:
T_A = 145^o C − (5V − 3.75V ) × 0.8A×84^o C /W = 57^o C
The AME2056 can be used above 57^oC, but the charging current will be reduced below 0.8A. The charging current can
be calculated:
I _BAT
=
145^o C − T_A
(V_CC −V_BAT ) ×θ _JA
According to the previous example with ambient temperature of 90^oC, the charging current is reduced to:
I _BAT
=
145^o C − 90^o C
(5 − 3.75)× 84
= 524mA
Layout Consideratons
The good thermal conduction PCB layout is very important to apply to maximize the available charging current. The
thermal path is from the die to the PCB. The PCB is the heat sink. The copper pads footprint should be as large as
possible and expand out to large copper areas to spread and dissipate the heat to the ambient. Other heat source must
be considered when designing a PCB layout because they will affect overall temperature rise and maximum charging
current.
V_CC Bypass Capacitor
Many types of capacitors can be used as input bypass capacitor. However, the high voltage transients can be
generated under some start-up conditions when using the self-resonant and high Q characteristics of ceramic capacitors.
Adding a 0.4Ω resistor in series with an X5R ceramic capacitors will minimize start-up voltage transients.
Rev. B.01
15