MIC2810 datasheet(13/18 Pages) MICREL

13 / 18 page

Micrel, Inc.

MIC2810

February 2008

M9999-022008-C

Device Functional Description

The MIC2810 is a power management IC with a single

integrated step-down regulator and two low dropout

regulators. LDO1 and LDO2 are 300mA low dropout

regulators supplied from the input voltage pins. The

step-down regulator is a 600mA PWM power supply. All

three regulators utilize a /LOWQ light load mode to

maximize battery efficiency under light load conditions.

This is achieved with a /LOWQ control pin that when

pulled low shuts down all the biasing and drive current

for the PWM regulator, along with reducing the current

limit of the two independent LDOs. When the /LOWQ pin

is pulled low, the MIC2810 draws only 30µA of operating

current. This mode allows the output to be regulated

through the LDO output which is capable of providing

60mA of output current. This method has the advantage

of producing a clean, low current, ultra-low noise output

in /LOWQ mode. During /LOWQ mode, the SW node

becomes high impedance, blocking current flow. Other

methods of reducing quiescent current, such as pulse

frequency modulation (PFM) or bursting techniques

create large amplitude and low frequency ripple voltages

that can be detrimental to system operation.

When more than 60mA is required, the /LOWQ pin can

be forced high, causing the MIC2810 to enter PWM

mode. In this case, the LDO output makes a "hand-off"

to the PWM regulator with virtually no variation in output

voltage. The LDO output then turns off allowing up to

600mA of current to be efficiently supplied through the

PWM output to the load.

Pin Functional Description

VIN/VIN1/VIN2

Three input voltage pins provide power to the switch

mode regulator, LDO1, and LDO2. VIN provides power

to the control circuitry of the DC/DC converter and

voltage reference circuitry shared by all the regulators in

the MIC2810. LDO1’s input voltage (VIN1) can go down

to 1.65V but LDO2 and the DC/DC converter input

voltages are limited to 2.7V minimum.

For the switch mode regulator VIN provides power to the

MOSFET along with current limiting sense circuitry. Due

to the high switching speeds, a 4.7µF capacitor is

recommended close to VIN and the power ground

(PGND) pin for bypassing. Please refer to the PCB

layout section for an example of an appropriate circuit

layout.

LDO

The LDO pin is the output of the linear regulator and

should be connected to the output of the step-down

PWM regulator. In /LOWQ mode (/LOWQ <0.2V), the

LDO provides the output voltage of the DC/DC regulator.

LDO1

Regulated output voltage of LDO1. Power is provided by

VIN1. Recommended output capacitance is 2.2µF.

LDO2

Regulated output voltage of LDO2. Power is provided by

VIN2. Recommended output capacitance is 2.2µF.

EN/EN1/EN2

All enable inputs are active high, requiring 1.0V for

guaranteed operation. EN provides logic control for the

DC/DC regulator. EN2 provides logic control for LDO2,

and EN1 provides logic control for LDO1. The enable

inputs are CMOS logic and cannot be left floating.

The enable pins provide logic level control of the

specified outputs. When all enable pins are in the off

state, supply current of the device is greatly reduced

(typically <1µA). When the DC/DC regulator is in the off

state, the output drive is 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. Do not drive any of the enable pins above the

supply voltage.

Power-On Reset (POR)

The power-on reset output is an open-drain N-Channel

device, requiring a pull-up resistor to either the input

voltage or output voltage for proper voltage levels. The

POR output has a delay time that is programmable with

a capacitor from the CSET pin to ground. The delay time

can be programmed to be as long as 1 second.

/LOWQ

The /LOWQ pin provides a logic level control between

the internal PWM switching regulator mode, and the low

noise linear regulator mode. With /LOWQ pulled low

(≤0.2V), quiescent current of the device is greatly

reduced by switching to a low noise linear regulator

mode that has a typical supply current of 38µA. In linear

(LDO) mode the output can deliver 60mA of current to

the output. By placing /LOWQ high (≥1V), the device

transitions into a constant frequency PWM step-down

regulator mode. This allows the device the ability to

efficiently deliver up to 600mA of output current at the

same output voltage.

/LOWQ mode also limits the output load of both LDO1

and LDO2 to <50mA.

BIAS

The BIAS pin supplies the power to the internal control

and reference circuitry. The bias is powered from VIN

through an internal 6Ω resistor. A small 0.1µF capacitor

is recommended for bypassing.

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