LTC4010 Datasheet, PDF (15/20 Pages) Linear Integrated Systems – High Efficiency Standalone Nickel Battery Charger

LTC4010
APPLICATIO S I FOR ATIO
FROM
ADAPTER
5.5V TO 34V
20k
G
R
Y
R1 10k
20µF
LTC4010
V_CC
FAULT TGATE
CHRG
READY
D1
6V
Q4
TO
SYSTEM
LOAD
BGATE
49.9k
TIMER PGND
GND
CHEM
SENSE
BAT
0.1µF
INTV_DD
V_CDIV
V_CELL
V_TEMP
10k
33nF
10µH
0.05Ω
20µF
68nF
NiMH PACK
WITH 10k NTC
4010 F07
Figure 7. Full-Featured 2A LTC4010 Application
P-channel MOSFET Q4 functions as a switch to connect
the battery to the system load whenever the DC input
adapter is removed. If the maximum battery voltage is less
than the maximum rated V_GS of Q4, diode D1 and resistor
R1 are not required. Otherwise choose the Zener voltage
of D1 to be less than the maximum rated V_GS of Q4. R1
provides a bias current of (V_BAT – V_ZENER)/(R1 + 20k) for
D1 when the input adapter is removed. Choose R1 to make
this current, which is drawn from the battery, just large
enough to develop the desired V_GS across D1.
While the LTC4010 is a complete, standalone solution,
Figure 8 shows that it can also be interfaced to a host mi-
croprocessor. The MCU can control the charger directly with
an open-drain I/O port connected to the V_TEMP pin, if that
port is low leakage and can tolerate at least 2V. The charger
state is monitored on the three LTC4010 status outputs.
Charging of NiMH batteries is selected in this example.
However, NiCd parameters could be chosen as well.
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 LTC4010 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 pre-
mature fast charge termination. If the MPU cannot reliably
perform this function, the battery should be disconnected
from the load with a rectifier or switch during charging.
Excessive battery load current variations, such as those
generated by a post-regulating PWM, can generate suffi-
cient voltage noise to cause the LTC4010 to prematurely
terminate a charge cycle and/or prematurely restart a fast
charge. In this case, it may be necessary to inhibit the
LTC4010 after charging is complete until external gas gauge
circuitry indicates that recharging is necessary. Shutdown
power is applied to the LTC4010 through the body diode
of the P-channel MOSFET in this application.
Waveforms
Sample waveforms for a standalone application during a
typical charge cycle are shown in Figure 9. Note that these
waveforms are not to scale and do not represent the
complete range of possible activity. The figure is simply
intended to allow better conceptual understanding and to
highlight the relative behavior of certain signals generated
by the LTC4010 during a typical charge cycle.
Initially, the LTC4010 is in low power shutdown as the
system operates from a heavily discharged battery. A DC
adapter is then connected such that V_CC rises above 4.25V
4010p
15