Datasheet

LTC4415
14
4415fa
Typical applicaTions
non-critical high current loads. If the status resistors are
pulled up through the keep-alive power source itself as
shown in Figure 6, the output voltage is limited to:
V
OUT
= V
KEEP_ALIVE
– V
gs(M1,2)
where V
gs(M1,2)
is the voltage drop from gate to source
of the composite NMOS device (M1 and M2). The pull-up
resistor, R1, consumes power from the keep-alive source
when the primary or backup sources supply power to the
load. The primary power source or backup battery supplies
power to the load when either of them are higher than the
output voltage.
Current limit on any of the diode power paths can be set
to automatically fold back as the output voltage drops (to
reduce power consumption), by switching out a resistor on
the CLIM pin, as shown in Figure 6 for diode 1. The gate
of NMOS M3 can optionally be fed from a resistor divided
output voltage to adjust the output voltage threshold of
current foldback.
Multiple Battery Charging
Figure 7 illustrates an application circuit for automatic dual
battery charging from a single charger. The battery with
lower voltage receives larger charging current until both
battery voltages are equal, then both are charged. While
both batteries are charging simultaneously, the higher
capacity battery gets proportionally higher current from
the charger. For Li-Ion batteries, both batteries achieve
the charger float voltage minus the forward regulation
voltage of 15mV. This concept can be extended to more
than two batteries using additional LTC4415. The STAT1,
STAT2 pins provide information as to when the batteries
are being charged. For intelligent control, the EN1/EN2
input pins can be used with a microcontroller as shown
in Figure 9 later in this section.
Figure 7. Dual Battery Charging from a Single Charger
PROG
EN
FAULT
BATSENS
TO µP
FROM µP
NTC
CHRG
PGND
10µF
PV
IN
V
INSENSE
BAT
IDET TIMER
R4
549Ω
R5
549Ω
C2
0.22µF
C1
10µF
V
IN
4.5V TO 5.5V
C3
0.1µF
SS
SW SENSE
LTC4001
L1
1.5µH
GNDSENS
R3
10k
25°C
R2
1k
D1
LED
R1
10k
IDEAL
50k
IDEAL
LTC4415
GND
EN1
4415 F07
CLIM1
CLIM2
STAT1
WARN1
WARN2
STAT2
EN2
IN2
IN1 OUT1
OUT2
BAT2
LOAD2
1.5k
1.5k
+
BAT1
+
LOAD1