Micrel, Inc.

MIC5311

March 2006

9

M9999-032706

(408) 955-1690

Functional Description

The MIC5311 is a high performance, low quiescent

current power management IC consisting of two µCap

low dropout regulators with a LowQ™ mode featuring

lower operating current. Both regulators are capable of

sourcing 300mA.

Enable 1 and 2

The enable inputs allow for logic control of both output

voltages with individual enable inputs. The enable input

is active high, requiring 1.0V for guaranteed operation.

The enable input is CMOS logic and cannot be left

floating.

LowQ™ Mode

The LowQ™ pin is logic level low, requiring <0.2V to

enter the LowQ™ mode. The LowQ™ pin cannot be left

floating. Features of the LowQ™ mode include lower

total quiescent current of typically 7uA.

Input Capacitor

Good bypassing is recommended from input to ground

to help improve AC performance. A 1µF capacitor or

greater located close to the IC is recommended. Larger

load currents may require larger capacitor values.

Bypass Capacitor

The internal reference voltage of the MIC5311 can be

bypassed with a capacitor to ground to reduce output

noise and increase input ripple rejection (PSRR). A

quick-start feature allows for quick turn-on of the output

voltage. The recommended nominal bypass capacitor is

0.01µF, but an increase will result in longer turn on

Output Capacitor

Each regulator output requires a 2.2µF ceramic output

capacitor for stability. The output capacitor value can be

increased

to

improve

transient

response,

but

performance has been optimized for a 2.2µF ceramic

type output capacitor. X7R/X5R dielectric-type ceramic

capacitors

are

recommended

because

of

their

temperature performance. X7R-type capacitors change

capacitance by 15% over their operating temperature

range and are the most stable type of ceramic

capacitors. Z5U and Y5V dielectric capacitors change

value by as much as 50% to 60% respectively over their

operating temperature ranges. To use a ceramic chip

capacitor with Y5V dielectric, the value must be much

higher than a X7R ceramic capacitor to ensure the same

minimum capacitance over the equivalent operating

temperature range.

Thermal Considerations

The MIC5311 is designed to provide 300mA of

continuous current per channel in a very small MLF

package. Maximum power dissipation can be calculated

based on the output current and the voltage drop across

the part. To determine the maximum power dissipation

of the package, use the junction-to-ambient thermal

resistance of the device and the following basic

equation:

die,

125°C,

and

is

the

ambient

operating

temperature.

θ

examples of the junction-to-ambient thermal resistance

for the MIC5311.

Table 1. MLF™ Thermal Resistance

The actual power dissipation of the regulator circuit can

be determined using the equation:

conditions that are critical to the application will give the

maximum operating conditions for the regulator circuit.

For example, when operating the MIC5311 at 60°C with

a minimum footprint layout, the maximum load currents

can be calculated as follows:

The junction-to-ambient thermal resistance for the

minimum footprint is 63°C/W, from Table 1. The

maximum power dissipation must not be exceeded for

proper operation. Using a lithium-ion battery as the

can be calculated as follows:

Package

θθθθ

Minimum Footprint

θθθθ

JC

3x3 MLF™-10

63°C/W

2°C/W