Micrel, Inc.
MIC2808
VIN
Device Functional Description
VIN provides power to the LDO1 and the LDO2 control
sections of the MIC2808. 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*.
The MIC2808 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
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 (95mꢀ typical) P-
Channel MOSFET switch. The feedback signal provides
the control path to set the output at three times the DAC
voltage.
amplifier applications.
Also where high power is
required, the step-down PWM regulator has a bypass
mode where an internal 95mꢀ switch connects the OUT
and PVIN pins together.
SW
Pin Functional Description
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.
PVIN
PVIN (Power VIN) provides power to the MOSFETs for
the step-down switching regulator section of the
MIC2808, 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*.
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*.
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*.
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*.
DAC
The DAC pin is the control pin that sets the output
voltage of the step-down regulator. The Output voltage is
3X the voltage set on the DAC pin (VOUT = VDAC x 3).
When 1.2V or greater is applied to the DAC pin, the
MIC2808’s step-down regulator enters bypass mode. In
bypass mode, the input supply is connected to the
output through a 95mꢀ P-Channel MOSFET.
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.
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).
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.
M9999-071709-A
July 2009
13
MICREL [ MICREL SEMICONDUCTOR ]
