LTC4011 Linear Technology, LTC4011 Datasheet - Page 18

• Manufacturer Part Number: LTC4011
• Description: High Efficiency Standalone Nickel Battery Charger
• Manufacturer: Linear Technology

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APPLICATIO S I FOR ATIO
LTC4011
previously discussed. The application includes all average
cell voltage and battery temperature sensing circuitry
required for the LTC4011 to utilize its full range of charge
qualification, safety monitoring and fast charge termina-
tion features. A green LED indicates valid DC input voltage
and installed battery, while a pair of red LEDs indicates
charging. A yellow LED indicates fault conditions. The
grounded CHEM pin selects the NiMH charge termination
parameter set.
While the LTC4011 is a complete, standalone solution,
Figure 9 shows that it can also be interfaced to a host
microprocessor. The MCU can control the charger directly
with an open-drain I/O port connected to the V
that port is low leakage and can tolerate at least 2V. The
charger state is monitored on the four LTC4011 status
outputs. Charging of NiMH batteries is selected in this
example. However, NiCd (CHEM → V
be chosen as well.
18
4
4.5V TO 34V
ADAPTER
FROM
U
20k
3k
G
U
3k
R
3k
R
49.9k
W
RT
3k
Figure 8. Full-Featured 2A LTC4011 Application
Y
) parameters could
0.1µF
INFET
FAULT
CHRG
TOC
READY
DCIN
TIMER
GND
CHEM
V
INTV
U
RT
TEMP
LTC4011
DD
10k
R5
BGATE
SENSE
TGATE
V
pin, if
PGND
V
V
TEMP
CDIV
CELL
BAT
V
CC
33nF
10k
Unlike all of the other applications discussed so far, the
battery continues to power the system during charging.
The MCU could be powered directly from the battery or
from any type of post regulator operating from the battery.
In this configuration, the LTC4011 relies expressly on the
ability of the host MCU to know when load transients will
be encountered. The MCU should then pause charging
(and thus –∆V processing) during those events to avoid
premature fast charge termination. If the MPU cannot
reliably perform this function, full PowerPath control
should be implemented. Excessive battery load current
variations, such as those generated by a post-regulating
PWM, can generate sufficient voltage noise to cause the
LTC4011 to prematurely terminate a charge cycle and/or
prematurely restart a fast charge. In this case, it may be
necessary to inhibit the LTC4011 after charging is com-
plete until external gas gauge circuitry indicates that
recharging is necessary. Shutdown power is applied to the
LTC4011 through the body diode of Q2 in this application.
R2
22nF
51k
10µF
10µH
0.05Ω
30.9k
10.7k
6V
4011 F08
NiCd PACK
WITH 10k NTC
(2AHr)
10µF
TO
SYSTEM
LOAD
4011p