ADP2165ACPZ-1.8-R7 datasheet(13/23 Pages) AD

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Data Sheet

ADP2165/ADP2166

Rev. B | Page 13 of 23

SOFT START

The SS pin is used to program the soft start time. By connecting

a capacitor between the SS and GND pins, the internal current

then charges this capacitor and establishes the soft start ramp-up.

The soft start time can be calculated by the following equation:

= 6

where:

CSS is the soft start capacitance.

ISS is the soft start pull-up current (3.5 µA).

If the output voltage is precharged prior to startup, the

ADP2165/ADP2166 prevent reverse inductor current that

discharges the output capacitor until the soft start voltage

exceeds the voltage on the FB pin.

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

soft start capacitor discharges.

TRACKING

The ADP2165/ADP2166 have a tracking input feature, TRK,

that allows the output voltage to track another voltage (master

voltage). It is especially useful in core and I/O voltage tracking for

field programmable gate arrays (FPGAs), digital signal processors

(DSPs), and application specific integrated circuits (ASICs).

The internal error amplifier includes three positive inputs: the

internal reference voltage, the soft start voltage, and the TRK

voltage. The error amplifier regulates the FB voltage to the

lowest of the three voltages. To track a master voltage, tie the

TRK pin to a resistor divider from the master voltage.

If the TRK function is not used, connect the TRK pin to the VREG.

POWER-GOOD (PGOOD)

The PGOOD pin is an active high, open-drain output that requires

a pull-up resistor. A logic high on the PGOOD pin indicates

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

voltage) is within ±10% of the desired value. In addition, there is a

16-cycle waiting period after the FB pin is detected as being

within the ±10% range. A logic low on the PGOOD pin indicates

that the voltage on the FB pin is not within ±10% of the desired

value. Similarly, there is a 16-cycle delay to deassert PGOOD.

PEAK CURRENT-LIMIT AND SHORT-CIRCUIT

PROTECTION

The ADP2165/ADP2166 have a peak current-limit protection

circuit to prevent current runaway. When the inductor peak

current reaches the current-limit value, the high-side NFET

turns off, and the low-side NFET turns on until the next cycle,

while the overcurrent counter increments. If the overcurrent

counter count exceeds 10, the device enters hiccup mode, and

the high-side NFET and low-side NFET both turn off. The

devices remain in this mode for seven times the soft start time

and then attempt to restart from the soft start. If the current-

limit fault clears, the devices resume normal operation.

Otherwise, they reenter hiccup mode after counting 10 current-

limit violations.

OVERVOLTAGE PROTECTION

The ADP2165/ADP2166 provide an overvoltage protection

feature that protects the system from an output short to a higher

voltage supply or from a strong unload transient. If the feedback

voltage increases to 0.7 V, the internal high-side NFET turns off

and the low-side NFET turns on until the current through the

low-side NFET reaches the negative current limit. Thereafter, both

the high-side and low-side NFET are held in the off state until

the voltage at FB decreases to 0.63 V, and the devices resume

normal operation.

UNDERVOLTAGE LOCKOUT

Undervoltage lockout circuitry is integrated in the ADP2165/

ADP2166. If AVIN drops below 2.5 V, the devices turn off.

When the AVIN voltage rises above 2.6 V, the soft start period

initiates, and the devices are enabled.

THERMAL SHUTDOWN

In the event that the junction temperatures of the ADP2165/

ADP2166 rise above 150°C, the thermal shutdown circuit turns

the regulator off. 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 ADP2165/ADP2166 do not

return to operation until the on-chip temperature drops below

125°C. When coming out of thermal shutdown, soft start initiates.

ADP2165ACPZ-1.8-R7 Datasheet(PDF) 13 Page - Analog Devices

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