ZSPM4012B Datasheet

© 2016 Integrated Device Technology, Inc.

13

January 27, 2016

Figure 3.2

Monitor and Control Logic Functionality

TSD

Filter

VCC-UV

Filter

Internal

POR

Filter

Filter

EN

VOUT-UV

Filter

PG

ENABLE

REGULATOR

VOUT-OV

Filter

IOCD

OCD_Filter

TRI-STATE

VSW OUTPUT

3.2.

Internal Protection Details

3.2.1.

Internal Current Limit

The current through the high-side FET is sensed on a cycle-by-cycle basis, and if the current limit is reached, the

over-current detection (OCD) circuit will abbreviate the cycle. The device also senses the FB pin to identify hard

short conditions and will direct the VSW output to skip 4 cycles if the current limit occurs when FB is low. This

allows current built up in the inductor during the minimum on-time to decay sufficiently. The current limit is always

active when the regulator is enabled. Soft start ensures that current limit does not prevent regulator startup.

An additional feature of the over-current protection circuitry is that under extended over-current conditions, the

device will automatically disable. A simple toggle of the EN enable pin will return the device to normal operation.

3.2.2.

Thermal Shutdown

If the temperature of the die exceeds 170°C (typical), the thermal shutdown (TSD) circuit will set the VSW outputs

to the tri-state level to protect the device from damage. The PG and all other protection circuitry will stay active to

inform the system of the failure mode. If the ZSPM4012B cools to 160°C (typical), it will attempt to start up again,

following the normal soft start sequence. If the device reaches 170°C, the shutdown/restart sequence will repeat.

3.2.3.

Voltage Reference Soft-Start

The voltage reference in this device is ramped at a rate of 4ms to prevent the output from overshoot during

startup. This ramp restarts whenever there is a rising edge sensed on the EN pin. This occurs in both the fixed

and adjustable versions. During the soft start ramp, current limit is still active and still protects the device if the

output is shorted.

3.2.4.

VCC Under-Voltage Lockout

The ZSPM4012B is held in the off state until VCC reaches 4.3V (typical). See section 1.4 for the input hysteresis.