Datasheet

LTC4063
16
4063fc
Protection Features
While the thermally regulated charger limits the junction
temperature to 105°C during normal operation, current
overload at the LDO regulator output may result in exces-
sive power dissipation. Internal circuitry limits the output
currents, allowing the battery charger and regulator to
be short-circuited to ground indefinitely. Furthermore, if
the junction temperature exceeds 150°C, both the bat-
tery charger and regulator will shut down. The LTC4063
becomes enabled again once the junction temperature
drops below 140°C. If the fault condition remains in
place, the part will thermal cycle between the shutdown
and enabled states.
The LTC4063 also protects against reverse conduction
from the LDO output to the battery input. This provides
protection if a discharged (low voltage) battery is powering
the LDO, and the output voltage is held above the battery
voltage by a backup battery or a second regulator circuit.
When the output voltage is higher than the battery voltage,
the reverse output current is typically less than 50µA.
Thermal
Considerations
In order to deliver maximum charge current under all
conditions, it is critical that the exposed metal pad on the
backside of the LTC4063 package is properly soldered to
the PC board ground. Correctly soldered to a 2500mm
2
double sided 1oz copper board, the LTC4063 has a ther-
mal resistance of approximately 40°C/W. Failure to make
thermal contact between the exposed pad on the backside
of the package and the copper board will result in thermal
resistances far greater than 40°C/W. As an example, a
correctly soldered LTC4063 can deliver over 800mA to a
applicaTions inForMaTion
battery from a 5V supply at room temperature. Without
a good backside thermal connection this number would
drop to much less than 500mA.
V
CC
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 an X5R
ceramic capacitor will minimize start-up voltage transients.
For more information, see Application Note 88.
Charge
Current Soft-Start and Soft-Stop
The LTC4063 includes a soft-start circuit to minimize the
inrush current at the start of a charge cycle. When a charge
cycle is initiated, the charge current ramps from zero to the
full-scale current over a period of approximately 100µs.
Likewise, internal circuitry slowly ramps the charge cur-
rent from full-scale to zero when the charger is shut down
or self terminates. This has the effect of minimizing the
transient current load on the power supply during start-up
and charge termination.
Reverse
Polarity Input Voltage Protection
In some applications, protection from reverse polarity volt-
age on V
CC
is desired. If the supply voltage is high enough,
a series blocking diode can be used. In other cases where
the voltage
drop must be kept low, a P-channel MOSFET
can be used (as shown in Figure 8).
V
CC
V
IN
4063 F08
LTC4063
DRAIN-BULK
DIODE OF FET
Figure 8. Low Loss Input Reverse Polarity Protection