Datasheet

LTC4010
17
4010fb
Sample Applications
Figures 6 through 8 detail sample charger applications of
various complexities. Combined with the Typical Application
on the first page of this data sheet, these figures demon-
strate some of the proper configurations of the LTC4010.
MOSFET body diodes are shown in these figures strictly
for reference only.
Figure 6 shows a minimum application, which might be
encountered in low cost NiCd fast charge applications.
The LTC4010 uses –∆V to terminate the fast charge state,
as no external temperature information is available.
Nonsynchronous PWM switching is employed to reduce
external component cost. A single LED indicates charging
status.
A
full-featured 2A LTC4010 application is shown in Figure 7.
The inherent voltage ratings of the V
CELL
, V
CDIV
, SENSE
and BAT pins allow charging of one to sixteen series nickel
cells in this application, governed only by the V
CC
overhead
limits previously discussed. The application includes all
average cell voltage and battery temperature sensing
circuitry required for the LTC4010 to utilize its full range
of charge qualification, safety monitoring and fast charge
termination features. The V
TEMP
thermister network allows
the LTC4010 to accurately terminate fast charge under a
applicaTions inForMaTion
variety of applied charge rates. Use of a synchronous PWM
topology improves efficiency and reduces excess heat
generation. LED D1 indicates valid DC input voltage and
installed battery, while LED D2 indicates charging. Fault
conditions are indicated by LED D3. The grounded CHEM
pin selects the NiMH charge termination parameter set.
P-channel MOSFET Q1 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 Q1, diode D4 and resistor R1
are not required. Otherwise choose the Zener voltage
of D4 to be less than the maximum rated V
GS
of Q1. R1
provides a bias current of (V
BAT
– V
ZENER
)/(R1 + 20k) for
D4 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 D4.
While the LTC4010 is a complete, standalone solution,
Figure 8 shows that it can also be interfaced to a host
microprocessor. The host 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.
Figure 6. Minimum 1 Amp LTC4010 Application
FAULT
CHRG
READY
V
CC
TGATE
V
CDIV
V
CELL
CHEM
V
TEMP
LTC4010
TIMER
INTV
DD
GND
SENSE
BAT
FROM
ADAPTER
12V
10µH
TO
SYSTEM
LOAD
0.1Ω
NiCd
PACK
(1AHr)
4010 F06
3k
49.9k
10k
8.66k
0.1µF
10µFR2
33nF
10µF
BGATE
PGND