ADP2381AREZ-R7 datasheet(14/28 Pages) AD

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ADP2381

Data Sheet

Rev. 0 | Page 14 of 28

If the output voltage is charged prior to turn-on, the ADP2381

prevents the low-side MOSFET from turning on, which

discharges the output voltage until the soft start voltage exceeds

the voltage on the FB pin.

When the regulator is disabled or a current fault happens, the

soft start capacitor is discharged, and the internal digital soft

start is reset to 0 V.

POWER GOOD

The power-good (PGOOD) pin is an active high, open-drain

output that requires a pull-up resistor. A logic high indicates

that the voltage at the FB pin (and, therefore, the output

voltage) is above 95% of the reference voltage and there is a

1024 cycle waiting period before PGOOD is pulled high. A logic

low indicates that the voltage at the FB pin is below 90% of the

reference voltage and there is a 16-cycle waiting period before

PGOOD is pulled low.

PEAK CURRENT LIMIT AND SHORT-CIRCUIT

PROTECTION

The ADP2381 has a peak current-limit protection circuit to

prevent current runaway. During soft start, the ADP2381 uses

frequency foldback to prevent output current runaway. The

switching frequency is reduced according to the voltage on the

FB pin, which allows more time for the inductor to discharge.

The correlation between the switching frequency and FB pin

voltage is shown in Table 5.

Table 5. Switching Frequency and FB Pin Voltage

FB Pin Voltage

Switching Frequency

FB ≥ 0.4 V

0.4 V > V

FB ≥ 0.2 V

SW/2

FB < 0.2 V

SW/4

For heavy load protection, the ADP2381 uses hiccup mode for

overcurrent protection. When the inductor peak current reaches

the current-limit value, the high-side MOSFET turns off and

the low-side driver turns on until the next cycle, while the

overcurrent counter increments. If the overcurrent counter

reaches 10, or the FB pin voltage falls to ≤0.4 V after the soft

start, the regulator enters hiccup mode. The high-side MOSFET

and low-side MOSFET are both turned off. The regulator

remains in this mode for 4096 clock cycles and then attempts to

restart. If the current limit fault is cleared, the regulator resumes

normal operation. Otherwise, it reenters hiccup mode.

The ADP2381 also provides a sink current limit to prevent the

low-side MOSFET from sinking a lot of current from the load.

When the voltage across the low-side MOSFET exceeds the

sink current-limit threshold, which is typically 20 mV, the low-

side MOSFET turns off immediately for the rest of this cycle.

Both high-side and low-side MOSFETs turn off until the next

clock cycle.

In some cases, the input voltage (PVIN) ramp rate is too slow or

the output capacitor is too large to support the setting regulation

voltage during the soft start, causing the regulator to enter

hiccup mode. To avoid such cases, use a resistor divider at the

UVLO pin to program the UVLO input voltage, or use a longer

soft start time.

OVERVOLTAGE PROTECTION (OVP)

The ADP2381 provides an overvoltage protection feature to

protect the system against an output shorting to a higher voltage

supply or a strong load transient occurring. If the feedback

voltage increases to 0.7 V, the internal high-side MOSFET and

low-side driver are turned off until the voltage at FB decreases to

0.63 V. At that time, the ADP2381 resumes normal operation.

UNDERVOLTAGE LOCKOUT (UVLO)

The UVLO pin enable threshold is 1.2 V with 100 mV

hysteresis.

The ADP2381 has an internal voltage divider consisting of two

resistors from PVIN to GND, 320 kΩ for the high-side resistor

and 125 kΩ for the low-side resistor. An external resistor divider

from PVIN to GND can be used to override the internal resistor

divider.

THERMAL SHUTDOWN

In the event that the ADP2381 junction temperatures rise above

150°C, the thermal shutdown circuit turns off the regulator.

Extreme junction temperatures can be the result of high current

operation, poor circuit board design, and/or high ambient

temperature. A 25°C hysteresis is included so that when thermal

shutdown occurs, the ADP2381 does not return to operation

until the on-chip temperature drops below 125°C. Upon

recovery, soft start is initiated prior to normal operation.

ADP2381AREZ-R7 数据表(PDF) 14 Page - Analog Devices

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