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Data Sheet

ADP1031

Rev. A | Page 25 of 38

Flyback Regulator Overcurrent Protection

The flyback regulator features a current-limit function that senses

the forward current in the switching metal-oxide semiconductor

field effect transistor (MOSFET) on a cycle by cycle basis. If the

current exceeds the ILIM (FLYBACK) threshold, the switch turns off.

Flyback Regulator Overvoltage Protection

The flyback regulator of the ADP1031 implements a number of

OVP methods to detect and prevent an overvoltage condition

on the flyback regulator output, such as the following:

•

If the voltage on the FB1 pin exceeds VFB1 by 10% for the

adjustable output version, or the VOUT1 pin exceeds the

factory programmed VOUT1 by 10% for the fixed output

version, an OVP fault will be detected, which prevents the

flyback regulator switch from turning on. The flyback

regulator primary switch stays off until the OVP condition

is no longer present.

•

If communication across the isolation barrier from the

secondary controller to the primary controller fails, the

flyback regulator shuts down and a new soft start power-up

cycle initiates.

•

If the voltage on the output of the flyback regulator exceeds

the severe overvoltage threshold (SOVPFLYBACK), the primary

controller does not turn on the primary side switch. The

flyback regulator primary switch stays off until the voltage on

the VOUT1 pin falls below the SOVPFLYBACK − SOVPFLYBACK_HYST

threshold.

BUCK REGULATOR

Buck Regulator Operation

The step-down, dc-to-dc (or buck) regulator in the ADP1031

uses a current mode controlled scheme, operating at a fixed

frequency set by an internal oscillator. Current mode uses a fast

inner current-controlled loop to regulate peak inductor current

and a slower outer loop to adjust the current loop to regulate

the output voltage. At the start of each oscillator cycle, the high-

side MOSFET switch turns on, applying the input voltage to one

end of the inductor, which normally causes the buck regulator

inductor current (IL_BUCK) to increase until the current sense

signal crosses the peak inductor current threshold that turns

off the MOSFET switch. The error amplifier output sets this

threshold. During the high-side MOSFET off time, the inductor

current declines through the low-side MOSFET switch until

either the next oscillator clock pulse starts a new cycle that results

in continuous conduction mode (CCM) operation, or the inductor

current reaches zero, the low-side MOSFET switch is turned off,

and the control system waits for the next oscillator clock pulse

to start a new cycle, resulting in discontinuous mode (DCM)

operation. Under light load conditions, the regulator can skip

pulses to maintain regulation and increase power conversion

efficiency.

Buck Regulator UVLO

The step-down regulator of theADP1031 features an internal

undervoltage lockout circuit that monitors the input voltage to

the regulator or VOUT1. If the voltage at VOUT1 drops below

the internal threshold level of 4.5 V, the regulator turns off. If

the output at VOUT1 rises above the internal threshold, the

regulator soft start period initiates, and the regulator enables.

Buck Regulator Soft Start

The step-down regulator in the ADP1031 includes soft start

circuitry that ramps the output voltage in a controlled manner

during start-up, thereby limiting the inrush current.

Buck Regulator Current-Limit Protection

The step-down regulator in the ADP1031 includes a current-

limit protection circuit to limit the amount of forward current

through the high-side MOSFET switch. The inductor peak

current is monitored cycle by cycle to detect an overload

condition. When the overload condition occurs, the current-

limit protection limits the peak inductor current to ILIM (BUCK),

resulting in a drop in the output voltage.

Buck Regulator OVP

The step-down regulator of the ADP1031 features an OVP

circuit that monitors the output voltage. If the voltage on the

VOUT2 pin exceeds the nominal output voltage by 10%, the

step-down, dc-to-dc regulator stops switching until the voltage

falls below the threshold again.

Buck Regulator Active Pull-Down Resistor

The buck regulator has an active pull-down resistor that

discharges the output capacitor when the output of VOUT1

is between 1.23 V and 4.5 V. The pull-down resistor connects

between VOUT2 and SGND2.

ADP1031ACPZ-5-R7 数据表(PDF) 25 Page - Analog Devices

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