LTC4010_15 Datasheet, PDF (17/24 Pages) Linear Technology – High Efficiency Standalone Nickel Battery Charger

LTC4010
Applications Information
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
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.
FROM
ADAPTER
12V
3k
10µF
LTC4010
V_CC
FAULT TGATE
CHRG
READY
BGATE
49.9k
TIMER PGND
SENSE
GND
BAT
0.1µF
10k
V_CDIV
CHEM V_CELL
INTV_DD V_TEMP
8.66k
10µH
0.1Ω
R2
10µF
33nF
4010 F06
TO
SYSTEM
LOAD
NiCd
PACK
(1AHr)
Figure 6. Minimum 1 Amp LTC4010 Application
4010fb
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