LTC4063 LINER [Linear Technology], LTC4063 Datasheet - Page 16

• Manufacturer Part Number: LTC4063
• Description: Standalone Linear Li-Ion Charger with Micropower Low Dropout Linear Regulator
• Manufacturer: LINER [Linear Technology]

APPLICATIO S I FOR ATIO
LTC4063
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 battery
charger and regulator will shut down. The LTC4063 be-
comes 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 power-
ing 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
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
16
U
U
W
Figure 8. Low Loss Input Reverse Polarity Protection
U
V
IN
DIODE OF FET
DRAIN-BULK
2
V
battery from a 5V supply at room temperature. Without a
good backside thermal connection this number would
drop to much less than 500mA.
V
Many types of capacitors can be used for input bypassing,
however, caution must be exercised when using multi-
layer ceramic capacitors. Because of the self-resonant and
high Q characteristics of some types of ceramic capaci-
tors, 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
voltage on V
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).
CC
CC
LTC4063
Bypass Capacitor
4063 F08
CC
is desired. If the supply voltage is high
4063fb