Micrel, Inc.

MIC2807

February 2008

13

M9999-022008-B

Device Functional Description

The MIC2807 is a power management IC with a single

integrated step-down regulator and two low dropout

regulators. LDO1 is a 200mA low dropout regulator and

LDO2 is a 30mA low dropout regulator. The 500mA

pulse-width-modulated

(PWM)

step-down

regulator

utilizes a dynamically adjustable output voltage for

powering RF power amplifiers. By dynamically adjusting

the output power as necessary, battery life can be

dramatically improved in battery powered RF power

amplifier applications.

Also where high power is

required, the step-down PWM regulator has a bypass

mode where an internal 95mΩ switch shorts the OUT

and PVIN pins together.

Pin Functional Description

PVIN

PVIN (Power VIN) provides power to the MOSFETs for

the step-down switching regulator section of the

MIC2807, along with the current limit sensing circuitry.

Due to the high switching speeds, a minimum 1µF

capacitor is recommended close to PVIN and the power

ground (PGND) pin for bypassing*.

AVIN

AVIN (Analog VIN) provides power to the internal

reference and control section of the step-down regulator.

AVIN, VIN, and PVIN must all be tied together. Careful

layout should be considered to ensure high frequency

switching noise caused by PVIN is reduced before

reaching AVIN*.

DAC

The DAC pin is the control pin that sets the output

voltage of the step-down regulator. The Output voltage is

When 1.2V or greater is applied to the DAC pin, the

MIC2807’s step-down regulator enters bypass mode. In

bypass mode, the input supply is connected to the

output through a 95mΩ P-Channel MOSFET.

EN/EN1/EN2

The EN pin provides a logic level control of the step-

down regulator output. In the off state, supply current of

the device is greatly reduced (typically ≤1µA). Also, in

the off state, the output drive and bypass switch are

placed in a "tri-stated" condition, where both the high

side P-channel MOSFET and the low-side N-channel are

in an off or non-conducting state. EN1 provides logic

control for LDO1, and EN2 provides logic control for

LDO2. Placing a logic high voltage on any one of the

respective enable pins (EN, EN1 or EN2) will turn-on

(powering up the bias and control circuitry) that

respective regulator (DC/DC, LDO1 or LDO2). Do not

drive the enable pins above the supply voltage (AVIN

and VIN).

VIN

VIN provides power to the LDO1 and the LDO2 control

sections of the MIC2807. A minimum 1µF capacitor,

2.2µF recommended, should be placed as close as

possible between the VIN and AGND pins. VIN must

have the same voltage as AVIN*.

OUT

The OUT pin connects the internal bypass drain and the

feedback signal to the output. The bypass applies the

input voltage through a low resistance (95mΩ typical) P-

Channel MOSFET switch. The feedback signal provides

the control path to set the output at 3 times the DAC

voltage.

SW

The SW pin connects directly to the inductor and

provides the switching current necessary to operate in

PWM mode. Due to the high speed switching on this pin,

the switch node should be routed away from sensitive

nodes.

PGND

PGND (Power GND) is the ground path for the

MOSFETs in the step-down regulator section. The

current loop for the power ground should be as small as

possible and separate from the analog ground (AGND)

loop*.

AGND

AGND (Analog GND) is the ground path for the biasing

and control circuitry. The current loop for the signal

ground should be separate from the Power ground

(PGND) loop*.

LDO1

Regulated output voltage of the LDO1. Power is

provided by VIN. Recommended output capacitance is

2.2µF.

LDO2

Regulated output voltage of the LDO2. Power is

provided by VIN. Recommended output capacitance is

1µF.

BYP

Filter capacitor for the voltage reference for the LDO1

and the LDO2. A 100nF capacitor is recommended from

the BYP pin to ground.

* Refer to PCB layout section of this data sheet for optimal layout

principles.