MIC2619 datasheet(8/15 Pages) MIC

8 / 15 page

Micrel, Inc.

MIC2619

March 2010

M9999-030410-A

Functional Diagram

MIC2619 Block Diagram

Functional Description

The MIC2619 is a constant frequency, PWM current

mode boost regulator. It is composed of an oscillator,

slope compensation ramp generator, current amplifier,

gm error amplifier, PWM generator, and bipolar output

transistor. The oscillator generates a 1.2MHz clock

which triggers the PWM generator to turn on the output

transistor and resets the slope compensation ramp

generator. The current amplifier is used to measure

switch current by amplifying the voltage signal from the

internal sense resistor. The output of the current

amplifier is summed with the output of the slope

compensation ramp generator. This summed current-

loop signal is then fed to one of the inputs of the PWM

generator.

The gm error amplifier measures the feedback voltage

through the external feedback resistors and amplifies the

error between the detected signal and the 1.265V

reference voltage. The output of the gm error amplifier

provides the voltage-loop signal that is fed to the other

input of the PWM generator. When the current-loop

signal exceeds the voltage loop signal, the PWM

generator turns off the bipolar output transistor. The next

clock

period

initiates

the

switching

cycle,

maintaining the constant frequency current-mode PWM

control.

VIN

VIN provides power to the control and reference circuitry

as well as the switch mode regulator MOSFETs. Due to

the high speed switching, a 1µF capacitor is

recommended as close as possible to the VIN and GND

pin.

The enable pin provides a logic level control of the

output. In the off state, supply current of the device is

greatly reduced (typically <0.1µA). Also, in the off state,

the output drive is placed in a “tri-stated” condition,

where the bipolar output transistor is in an “off” state or

non-conducting state.

OVP

The OVP pin provides over-voltage protection on the

output of the MIC2619. When the OVP circuit is tripped,

the output voltage remains at the set OVP voltage.

Because the OVP circuit operates at a lower frequency

than the feedback circuit, output ripple will be higher

while in an OVP state. OVP requires a resistor divider

network to the output and GND to set the OVP voltage.

If the output voltage overshoots the set OVP voltage,

then the MIC2619 OVP circuit will shut off the switch;

saving itself and other sensitive circuitry downstream.

The accuracy of the OVP pin is ±5% and therefore

should be set above the output voltage to ensure noise

or other variations will not cause a false triggering of the

OVP circuit.

MIC2619 Datasheet(PDF) 8 Page - MIC GROUP RECTIFIERS

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