LTC4415
16
4415fa
Figure 10. Parallel Diodes with Current Limit Foldback and Reverse Polarity Protection
output falls below a threshold set by the resistor divider
on EN1 pin. This arrangement results in current limit
foldback, reducing the current limit of the parallel diodes
to that of only diode 2 when the output voltage falls, thus
controlling power dissipation.
An optional Schottky diode can be inserted in series with
the chip ground as shown in Figure 10 to protect LTC4415
against input power source reverse polarity. The presence
of the Schottky shifts the UVLO and enable pin thresholds
by a voltage equal to the forward voltage drop of the
Schottky diode.
Power Backup Using Supercapacitors and Optional
Keep-Alive Cell
An application of dual backup power is shown on the last
page of this data sheet. Diode 2 provides power to the
triple DC/DC converter (LTC3521) when the primary input
power (V
DD
) is available, possibly from a wall adapter. When
the input power falls below the supercapacitor voltage,
the supercapcitor provides power to the LTC3521. The
supercapacitor charger (LTC3625) provides a power failure
comparator output signal (PFO) when its input voltage
falls below a preset voltage defined by the resistive divider
on the PFI input. The PFO signal is available to start the
shutdown of high current applications. When the super-
capacitor discharges to a voltage level determined by the
resistor divider on EN1 input of LTC4415, the wired-AND
status signal of LTC4415 pulls up because neither of the
diode paths in LTC4415 are conducting and the coin cell
provides power through a back-to-back connected pair
of NFETs, M1 and M2. The wired-AND status signal is
available to signal that only low current circuits such as
real-time clock or memory remain enabled while operating
from the coin cell.
Figure 9. Microcontrolled PowerPath Monitoring and Control
Typical applicaTions
IDEAL
IDEAL
LTC4415
GND
EN1
MN1
IRLML2402
470k
4415 F09
4.7µF
LOAD
CLIM1
CLIM2
STAT1
WARN1
WARN2
STAT2
EN2
IN2
IN1 OUT1
OUT2
PRIMARY
POWER
SOURCE
AUXILLIARY
POWER
SOURCE
MICRO-
CONTROLLER
IDEAL
IDEAL
LTC4415
GND
EN1
470k
4415 F10
LOAD
CLIM1
CLIM2
STAT1
WARN1
WARN2
STAT2
EN2
IN2
D1
1N5817
IN1 OUT1
OUT2
POWER
SOURCE
ENABLE
