Datasheet
Data Sheet ADP1850
Rev. A | Page 15 of 32
SHORT-CIRCUIT AND CURRENT-LIMIT
PROTECTION
SHUTDOWN CONTROL
The EN1 and EN2 pins are used to enable or disable Channel 1
and Channel 2 of the ADP1850. The precision enable (minimum)
threshold for EN1/EN2 is 0.57 V. When the voltage at EN1/EN2
rises above the threshold voltage, the ADP1850 is enabled and
starts normal operation after the soft start period. And when
the voltage at EN1/EN2 drops typically 30 mV (hysteresis)
below the threshold voltage, the switchers and the internal
circuits in the ADP1850 are turned off. Note that EN1/EN2
cannot shut down the LDO at VCCO, which is always active.
When the output is shorted or the output current exceeds the
current limit set by the current limit setting resistor (between
ILIMx and SWx) for eight consecutive cycles, the ADP1850
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 1 kΩ
resistor during an overcurrent or short-circuit event. Figure 28
shows that the ADP1850 on a high current application circuit is
entering current limit hiccup mode when the output is shorted.
For the purpose of start-up power sequencing, the startup of the
ADP1850 can be programmed by connecting an appropriate
resistor divider from the master power supply to the EN1/EN2
pin, as shown in Figure 29. 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.
CH3 500mV
CH1 10V
CH4 10A Ω
M2ms A CH1 11.2V
SW1
SS1
INDUCTOR CURRENT
1
3
4
09440-029
ADP1850
FB1
OR
FB2
EN1
OR
EN2
R
TOP
R
BOT
V
OUT1
R1
R2
MASTER
SUPPLY VOLTAGE
09440-030
Figure 29. Optional Power-Up Sequencing Circuit
THERMAL OVERLOAD PROTECTION
Figure 28. Current Limit Hiccup Mode, 20 A Current Limit
The ADP1850 has an internal temperature sensor that senses
the junction temperature of the chip. When the junction
temperature of the ADP1850 reaches approximately 155°C, the
ADP1850 goes into thermal shutdown, the converter is turned
off, and SS discharges toward zero through an internal 1 kΩ
resistor. At the same time, VCCO discharges to zero. When the
junction temperature drops below 135°C, the ADP1850 resumes
normal operation after the soft start sequence.