LTC4077 View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LTC4077' PDF : 16 Pages View PDF
LTC4077
APPLICATIO S I FOR ATIO
Thermal Limiting
An internal thermal feedback loop reduces the programmed
charge current if the die temperature attempts to rise above
a preset value of approximately 105°C. This feature protects
the LTC4077 from excessive temperature and allows the
user to push the limits of the power handling capability of
a given circuit board without risk of damaging the device.
The charge current can be set according to typical (not
worst-case) ambient temperature with the assurance that
the charger will automatically reduce the current in worst-
case conditions. DFN power considerations are discussed
further in the Applications Information section.
Using a Single Charge Current Program Resistor
In applications where the programmed wall adapter
charge current and USB charge current are the same, a
single program resistor can be used to set both charge
currents. Figure 2 shows a charger circuit that uses one
WALL
ADAPTER
LTC4077
DCIN
BAT
100mA
(USB, HPWR = LOW)
500mA
USB
PORT
1mF
1mF
USBIN
IUSB
HPWR
+
IUSBL
IDC
RISET
GND
2k
1%
4077 F02
Figure 2. Dual Input Charger Circuit. The Wall Adapter
Charge Current and USB Charge Currents (HPWR = High)
are Both Programmed to be 500mA. If USBIN is the Supply
and HPWR = Low, the Charge Current is 100mA
charge current program resistor. In this circuit, one registor
programs the same charge current for each input supply
(with HPWR = HIGH).
ICHRG(DC)
= ICHRG(USB)
=
1000V
RISET
The programmed charge current for USB supply with
HPWR in its low state is:
ICHRG(USBL)
=
200V
RISET
The LTC4077 can also program the wall adapter charge
current and USB charge current independently using two
program resistors, RIDC and RIUSB. Figure 3 shows a
charger circuit that sets the wall adapter charge current
to 800mA and the USB charge current to 500mA (HPWR
= high) or 50mA (HPWR = low).
WALL
ADAPTER
LTC4077
DCIN
BAT
USB
USBIN
POWER
1mF
1mF
RIUSBL
4.02k
1%
RIUSB
2k
1%
HPWR PWR
IUSBL CHRG
IUSB
IDC
GND
800mA (WALL)
500mA (USB,
HPWR = HIGH)
50mA (USB,
HPWR = LOW)
1k 1k
RIDC
1.24k
1%
+
4.2V
1-CELL
Li-Ion
BATTERY
4077 F03
Figure 3. Full Featured Dual Input Charger Circuit
4077f
12
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