LTC4097EDDB#PBF Linear Technology, LTC4097EDDB#PBF Datasheet - Page 15

• Manufacturer Part Number: LTC4097EDDB#PBF
• Manufacturer: Linear Technology
• Type: Battery Chargerr

Specifications of LTC4097EDDB#PBF

• Battery Type: Li-Ion/Li-Pol
• Output Voltage: 4.2V
• Operating Supply Voltage (min): 4.25V
• Operating Supply Voltage (max): 5.5V
• Operating Temp Range: -40C to 85C
• Mounting: Surface Mount
• Pin Count: 12
• Operating Temperature Classification: Industrial
• Lead Free Status / RoHS Status: Compliant

APPLICATIONS INFORMATION
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 charge cur-
rent program resistor. In this circuit, one resistor programs
the same charge current for each input supply.
The LTC4097 can also program the wall adapter charge
current and USB charge current independently using two
program resistors, R
charger circuit that sets the wall adapter charge current
to 800mA and the USB charge current to 500mA.
Stability Considerations
The constant-voltage mode feedback loop is stable without
any compensation provided a battery is connected to the
charger output. However, a 4.7µF 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 affected 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 20KΩ (I
50mA); however, additional capacitance on these nodes
reduces the maximum allowed program resistor.
ADAPTER
WALL
PORT
I
USB
CHRG DC
Figure 2. Dual Input Charger Circuit. The
Wall Adapter Charge Current and USB Charge
Current are Both Programmed to be 500mA
(
1µF
)
=
I
CHRG USB
R
ISET
1%
1µF
2k
(
IDC
)
DCIN
USBIN
IUSB
IDC
and R
=
LTC4097
1000
GND
R
ITERM
SET
HPWR
IUSB
BAT
V
. Figure 3 shows a
(USB, HPWR = LOW)
R
2k
1%
ITERM
100mA
500mA
+
4097 F02
4.2V
1-CELL
Li-Ion
BATTERY
CHRG
=
ADAPTER
WALL
PORT
Power Dissipation
When designing the battery charger circuit, it is not neces-
sary to design for worst-case power dissipation scenarios
because the LTC4097 automatically reduces the charge
current during high power conditions. The conditions
that cause the LTC4097 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 MOSFET pass device. Thus,
the power dissipation is calculated to be:
P
age (either DCIN or USBIN), V
and I
temperature at which the thermal feedback begins to
protect the IC is:
Example: An LTC4097 operating from a 5V USB adapter
(on the USBIN input) is programmed to supply 500mA
full-scale current to a discharged Li-Ion battery with a
voltage of 3.3V. Assuming θ
Considerations), the ambient temperature at which the
LTC4097 will begin to reduce the charge current is ap-
proximately:
USB
D
P
T
T
T
T
T
is the power dissipated, V
A
A
A
A
A
D
Figure 3. Full Featured Dual Input Charger Circuit
BAT
= 115°C – P
= 115°C – (V
= 115°C – (5V – 3.3V) • (500mA) • 60°C/W
= 115°C – 0.85W • 60°C/W = 115°C – 51°C
= 64°C
= (V
R
IUSB
1%
2k
is the charge current. The approximate ambient
1µF
CC
1.24k
– V
R
1%
IDC
1µF
BAT
D
CC
) • I
• θ
DCIN
USBIN
IUSB
IDC
– V
LTC4097
JA
BAT
GND
BAT
HPWR
ITERM
CHRG
VNTC
NTC
BAT
) • I
JA
CC
BAT
BAT
is 60°C/W (see Thermal
is the input supply volt-
R
2k
1%
R
ITERM
NTCBIAS
is the battery voltage
• θ
100k
JA
LTC4097
100mA/500mA (USB)
800mA (WALL)
R
100k
NTC
1k
+
15
4097 F03
4.2V
1-CELL
Li-Ion
BATTERY
4097f