LTC4075HVXEDD View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LTC4075HVXEDD' PDF : 16 Pages View PDF
LTC4075HVX
APPLICATIONS INFORMATION
Using a Single Charge Current Program Resistor
The LTC4075HVX can program the wall adapter charge
current and USB charge current independently using two
program resistors, RIDC and RIUSB. Figure 2 shows a
charger circuit that sets the wall adapter charge current
to 800mA and the USB charge current to 500mA.
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 3 shows a charger circuit that uses one
charge current program resistor.
WALL
ADAPTER
LTC4075HVX
DCIN
BAT
800mA (WALL)
500mA (USB)
USB
USBIN
+
PORT
1μF
1μF
IUSB
RIUSB
2k
1%
IDC
RIDC
1.24k
1%
ITERM
GND
RITERM
1k
1%
4075hvx F02
Figure 2. Dual Input Charger with Independant Charge Currents
WALL
ADAPTER
LTC4075HVX
DCIN
BAT
500mA
USB
USBIN
+
PORT
1μF
1μF
IUSB
IDC
RISET
2k
1%
ITERM
GND
RITERM
1k
1%
4075hvx F03
Figure 3. Dual Input Charger Circuit. The Wall Adapter Charge
Current and USB Charge Current are Both Programmed to be
500mA
In this circuit, the programmed charge current from both the
wall adapter supply is the same value as the programmed
charge current from the USB supply:
ICHRG−DC
=
ICHRG−USB
=
1000V
RISET
Stability Considerations
The constant-voltage mode feedback loop is stable without
any compensation provided a battery is connected to the
charger output. However, a 1μF capacitor with a 1Ω series
resistor is recommended at the BAT pin to keep the ripple
voltage low when the battery is disconnected.
When the charger is in constant-current mode, the charge
current program pin (IDC or IUSB) is in the feedback loop,
not the battery. The constant-current mode stability is af-
fected by the impedance at the charge current program pin.
With no additional capacitance on this pin, the charger is
stable with program resistor values as high as 20k (ICHRG
= 50mA); however, additional capacitance on these nodes
reduces the maximum allowed program resistor.
Power Dissipation
When designing the battery charger circuit, it is not neces-
sary to design for worst-case power dissipation scenarios
because the LTC4075HVX automatically reduces the charge
current during high power conditions. The conditions that
cause the LTC4075HVX to reduce charge current through
thermal feedback can be approximated by considering the
power dissipated in the IC. Most of the power dissipation
is generated from the internal charger MOSFET. Thus, the
power dissipation is calculated to be:
PD = (VIN – VBAT) • IBAT
PD is the dissipated power, VIN is the input supply volt-
age (either DCIN or USBIN), VBAT is the battery voltage
and IBAT is the charge current. The approximate ambient
temperature at which the thermal feedback begins to
protect the IC is:
TA = 125°C – PD • θJA
TA = 125°C – (VIN – VBAT) • IBAT • θJA
Example: An LTC4075HVX operating from a 5V wall
adapter (on the DCIN input) is programmed to supply
800mA full-scale current to a discharged Li-Ion battery
with a voltage of 3.3V.
12
4075hvxf
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