LTC4060_15 Datasheet, PDF (16/20 Pages) Linear Technology – Standalone Linear NiMH/NiCd Fast Battery Charger

LTC4060
TYPICAL APPLICATIO S
Full Featured 2A Charger Application
Figure 2 shows an application that utilizes the optional
temperature sensing and optional externally program-
mable automatic recharge features. It also has LEDs to
indicate charging status and the presence of sufficient
input supply voltage.
The PROG pin has a total resistance of 691Ω to ground
that programs the fast-charge current at the PNP’s emitter
to 2.02A (2A at the collector for beta of 100). The ARCT pin
voltage is programmed to 1.25V. When the battery cell
voltage falls below this automatic recharge will begin.
Optional capacitor C_BAT filters excessive contact bounce.
This circuit can be modified to charge a 4A-Hr battery at a
C/2 rate simply by doubling the C_TIMER capacitance.
Power Path Control
Proper power path control is an important consideration
when fast charging nickel cells. This control ensures the
system load remains powered at all times, but that normal
system operation and associated load transients do not
adversely affect the charging procedure. Figure 3 illus-
trates a 1A charger with power path control. When V_IN is
applied the forward biased Schottky diode will power the
load while the P-channel FET will disconnect the battery
from the load. When V_IN is removed, the FET will turn-on
to provide a low loss switch from the battery to the load,
and the diode will isolate V_IN. The ACP output signals the
presense of V_IN.
V_IN = 5V
R_HOT
4.42k
“CHARGE”
R_LED
330Ω
14
5
V_CC
13
SHDN ACP
15
3
CHRG SENSE
11
NTC
1
DRIVE
R_NTC
10k
R_PROG
115Ω
R_ARCT
576Ω
7 ^LTC4060 2
PROG BAT
8
4
ARCT TIMER
9
12
SEL0 CHEM
10
6
SEL1 PAUSE
GND
16
R_LED
330Ω
“AC”
MJD210
C_TIMER
1.5nF
4060 F02
C_BAT
10µF
+ 2-CELL
NiMH
BATTERY
Figure 2. Full Featured 2A Charger Application
16
R_LED
330Ω
“CHARGE”
R_PROG
1400Ω
V_IN = 5V
B220A
5
V_CC
13
SHDN ACP
15
3
CHRG SENSE
11 _NTC
DRIVE ¹
7 ^LTC4060 2
PROG BAT
8
4
ARCT TIMER
9
12
SEL0 CHEM
10
6
SEL1 PAUSE
GND
16
R_AC
10k
ACP
FZT948
FDG312P
C_TIMER
820pF
+ 2-CELL
NiMH
BATTERY ^*
TO LOAD
C_LOAD
10µF
4060 F03
*DRAIN SOURCE DIODE OF MOSFET
Figure 3. 1A Charger Application with Power Path Control
4060f