Datasheet

Data Sheet ADP1853
Rev. 0 | Page 15 of 28
SHORT-CIRCUIT AND CURRENT-LIMIT
PROTECTION
When the output is shorted or the output current exceeds the
current limit set by the current-limit setting resistor (between
ILIM and CS) for eight consecutive cycles, the ADP1853 shuts
off both the high-side and low-side drivers and restarts the soft
start sequence every 10 ms, which is known as hiccup mode.
The SS node discharges to zero through an internal 3 kΩ
resistor during an overcurrent or short-circuit event. Figure 22
shows that the ADP1853 on a high current application circuit
maintains current-limit hiccup mode when the output is
shorted.
Figure 22. Current-Limit Hiccup Mode, 20 A Current Limit
ENABLE/DISABLE CONTROL
The EN pin is used to enable or disable the controller ADP1853;
the precision enable typical threshold is 0.63 V. When the
voltage at EN rises above the threshold voltage, the controller is
enabled and starts normal operation after initialization of the
internal oscillator, references, settings, and the soft start period.
When the voltage at EN drops to typically 30 mV (hysteresis)
below the threshold voltage, the driver and the internal
controller circuits in the ADP1853 are turned off. The initial
settings are still valid; therefore re-enabling the controller does
not change the settings until the power at the VIN pin is cycled.
In addition, the EN signal does not shut down the LDO at
VCCO, which is always active when V
IN
is above the UVLO
threshold.
For the purpose of start-up power sequencing, the startup of the
ADP1853 can be programmed by connecting an appropriate
resistor divider from the master power supply to the EN pin, as
shown in Figure 23. For instance, if the desired start-up voltage
from the master power supply is 10 V, R1 and R2 can be set to
156 kΩ and 10 kΩ, respectively.
Figure 23. Optional Power-Up Sequencing Circuit
CH1 10V M2ms A CH1 11.2V
1
3
4
CH3 500mV CH4 10A Ω
SW
SS
INDUCTOR
CURRENT
10594-028
ADP1853
FBEN
R
TOP
R
BOT
V
OUT
R1
R2
MASTER
SUPPLY
VOLTAGE
10594-029