ADP1850ACPZ-R7 datasheet(15/32 Pages) AD

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Data Sheet

ADP1850

Rev. C | Page 15 of 32

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

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.

CH3 500mV

CH1 10V

CH4 10A

Ω

M2ms

A CH1

11.2V

SW1

SS1

INDUCTOR CURRENT

Figure 28. Current Limit Hiccup Mode, 20 A Current Limit

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.

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.

ADP1850

FB1

FB2

EN1

EN2

RTOP

RBOT

VOUT1

MASTER

SUPPLY VOLTAGE

Figure 29. Optional Power-Up Sequencing Circuit

THERMAL OVERLOAD PROTECTION

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.

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