LTC4052-4.2_15 Datasheet, PDF (9/12 Pages) Linear Technology – Lithium-Ion Battery Pulse Charger with Overcurrent Protection

LTC4052-4.2
APPLICATIO S I FOR ATIO
In addition, feedthrough vias or plated through holes (lo-
cated directly beneath the package and elsewhere) connect-
ing internal copper and backside copper layers help transfer
and spread the heat generated by the package.
Calculating Junction Temperature
Example: Find the maximum junction temperature for a
battery voltage of 4V (V_IN will collapse to approximately
V_BAT in the full charge mode), charge current of 1A and a
maximum ambient temperature of 75°C.
The power dissipated by the IC is:
P = (I_BAT • I_BAT • R_DS(ON)) + (V_IN • I_IN)
= (1A • 1A • 0.35Ω) + (4V • 0.7mA)
= 0.35 + 0.003
= 0.353W
The LTC4052 is available in an enhanced 8-pin MSOP
package which features an exposed copper pad on the
bottom of the package allowing it to be soldered directly to
the PC board copper for maximum heat transfer. This
greatly reduces the thermal resistance and increases the
power handling capability when compared to a standard
MSOP package. The junction to ambient thermal resis-
tance of this package when the backside of the package is
soldered to the PC board is approximately 35°C/W de-
pending on the copper area. The junction temperature rise
above ambient will be approximately:
(0.353W)(35°C/W) = 12.36°C
The maximum junction temperature will be equal to the
maximum junction temperature rise above ambient plus
the maximum ambient temperature or:
T_JMAX = 85°C + 12.36°C = 97.36°C
ACPR Output Pin
When the input voltage is 45mV higher than the voltage at
the BAT pin, the ACPR pin is pulled to ground to indicate
that the input supply (wall adapter) is applied. After the
input supply is removed, this pin will become high imped-
ance. An internal 100ms filter prevents the LTC4052 from
turning off if the voltage at the V_IN pin rings and gets too
close to V_BAT due to parasitic inductance.
Stop Charging
The charger is off when the voltage at the V_IN pin is less
than 45mV above V_BAT (sleep mode). The charge pump
and the internal pass transistor are turned off, and the
internal resistor divider is disconnected to reduce the
current drain on the battery in the sleep mode.
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