LTC4069EDC-4.4#TRM Linear Technology, LTC4069EDC-4.4#TRM Datasheet - Page 12

• Manufacturer Part Number: LTC4069EDC-4.4#TRM
• Description: BATT CHARGER, LI ON, 750MA, 6DFN
• Manufacturer: Linear Technology

Specifications of LTC4069EDC-4.4#TRM

• Battery Type: Li-Ion
• Input Voltage: 5.5V
• Battery Charge Voltage: 4.4V
• Charge Current Max: 750mA
• Battery Ic Case Style: DFN
• No. Of Pins: 6
• No. Of Series Cells: 1
• Operating Temperature Range: -40°C To
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

LTC4069
APPLICATIONS INFORMATION
LTC4069 will demand a charge current higher than the
current limit of the voltage supply, the supply voltage will
drop to the battery voltage plus 600mA times the “on”
resistance of the internal PFET. The “on” resistance of the
LTC4069 power device is approximately 450mΩ with a 5V
supply. The actual “on” resistance will be slightly higher
due to the fact that the input supply will drop to less than
5V. The power dissipated during this phase of charging
is less than 240mW. That is a 76% improvement over the
non-current limited supply power dissipation.
USB and Wall Adapter Power
Although the LTC4069 allows charging from a USB port,
a wall adapter can also be used to charge Li-Ion batteries.
Figure 4 shows an example of how to combine wall adapter
and USB power inputs. A P-channel MOSFET, MP1, is used
to prevent back conducting into the USB port when a wall
adapter is present and Schottky diode, D1, is used to prevent
USB power loss through the 1k pull-down resistor.
Typically a wall adapter can supply signifi cantly more
current than the 500mA-limited USB port. Therefore, an
N-channel MOSFET, MN1, and an extra program resistor
are used to increase the charge current to 750mA when
the wall adapter is present.
Stability Considerations
The LTC4069 contains two control loops: constant-voltage
and constant-current. The constant-voltage loop is stable
without any compensation when a battery is connected
with low impedance leads. Excessive lead length, however,
may add enough series inductance to require a bypass
12
ADAPTER
5V WALL
POWER
750mA
500mA
Figure 4. Combining Wall Adapter and USB Power
I
I
USB
CHG
CHG
MP1
1k
D1
MN1
V
CC
LTC4069
4.02k
PROG
BAT
I
CHG
2k
+
4069 F04
Li-Ion
BATTERY
SYSTEM
LOAD
capacitor of at least 1μF from BAT to GND. Furthermore,
a 4.7μF capacitor with a 0.2Ω to 1Ω series resistor from
BAT to GND is required to keep ripple voltage low when
the battery is disconnected.
High value capacitors with very low ESR (especially
ceramic) may reduce the constant-voltage loop phase
margin. Ceramic capacitors up to 22μF may be used
in parallel with a battery, but larger ceramics should be
decoupled with 0.2Ω to 1Ω of series resistance.
In constant-current mode, the PROG pin is in the feedback
loop, not the battery. Because of the additional pole created
by the PROG pin capacitance, capacitance on this pin must
be kept to a minimum. With no additional capacitance on
the PROG pin, the charger is stable with program resistor
values as high as 25k. However, additional capacitance
on this node reduces the maximum allowed program
resistor. The pole frequency at the PROG pin should be
kept above 100kHz. Therefore, if the PROG pin is loaded
with a capacitance, C
be used to calculate the maximum resistance value for
R
Average, rather than instantaneous, battery current may
be of interest to the user. For example, if a switching power
supply operating in low current mode is connected in
parallel with the battery, the average current being pulled
out of the BAT pin is typically of more interest than the
instantaneous current pulses. In such a case, a simple RC
fi lter can be used on the PROG pin to measure the average
Figure 5. Isolating Capacitive Load on the PROG Pin and Filtering
PROG
R
PROG
:
≤
LTC4069
2
GND
π
PROG
•
10
5
1
PROG
•
C
R
PROG
PROG
10k
, the following equation should
4069 F05
C
FILTER
CHARGE
CURRENT
MONITOR
CIRCUITRY
4069fb