MIC2033 datasheet(13/20 Pages) MICREL

13 / 20 page

Micrel, Inc.

MIC2033

August 2012

M9999-082012-A

Functional Description

The MIC2033 is a high-side MOSFET power distribution

switch providing increased system reliability utilizing 5%

current limit accuracy. The MIC2033 has an operating

input voltage range from 2.5V to 5.5V and is internally

current limited and has thermal shutdown that protects

the device and system.

Soft-Start

Soft-start reduces the power supply input surge current

at startup by controlling the output voltage rise time. The

input surge appears while the output capacitor is

charged up. A slower output rise time will draw a lower

input surge current.

During soft-start, an internal current sink discharges the

external capacitor at CSLEW to ground to control the

ramp of the output voltage. The output voltage rise time

is dependent upon the value of CCSLEW, the input voltage,

output voltage, and the current limit. The value of the

CSLEW external capacitor is recommended to be in the

range of 0.1µF to 1µF.

Input Capacitor

A 1µF to 10µF ceramic input capacitor is recommended

for most applications.

The input capacitor must be placed on the same side of

the board and next to the MIC2033 to minimize the

voltage ringing during transient and short circuit

conditions. It is also recommended to use two vias for

each end of the capacitor to connect to the power and

ground plane.

X7R

X5R

dielectric

ceramic

capacitors

are

recommended

because

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% and 60% respectively over their operating

temperature ranges. To use a ceramic chip capacitor

with Y5V dielectric, the value must be much higher than

an X7R ceramic or a tantalum capacitor to ensure the

same capacitance value over the operating temperature

range.

Output Capacitor

The output capacitor type and placement criteria are the

same as the input capacitor. See the Input Capacitor

section for a detailed description.

Enable

The MIC2033 offers either an active high or active low

enable input (EN) that allows ON/OFF control of the

switch output. The current through the device reduces to

near “zero” when the device is shutdown, with only

microamperes of leakage current. The EN input may be

directly tied to VIN or driven by a voltage that is equal to

or less than VIN, but do not leave this pin floating.

Current Limit

The MIC2033 is available with four fixed current limit

settings: 0.5A, 0.8A, 1A, and 1.2A. If the output current

exceeds the set current limit, then the MIC2033 switch

will enter constant current limit mode. The maximum

allowable current limit may be less than the full specified

and/or expected current if the MIC2033 is not mounted

on a circuit board with sufficiently low thermal resistance.

The MIC2033 responds within 10µs to short circuits to

limit the output current and also provides an output fault

flag that will assert (low) for an over current condition

that lasts longer than 32ms.

Thermal Design

To help reduce the thermal resistance, the ePad

(underneath the IC) should be soldered to the PCB

ground and the placement of thermal vias either

underneath or near the ePad is highly recommended.

Thermal design requires the following application-

speciﬁc parameters:

 Maximum ambient temperature (TA)

 Output current (IOUT)

 Input voltage (VIN)

 Current Limit (ILIMIT)

When the MIC2033 is in constant current limit mode, it

may exceed the over temperature threshold. If this

occurs, the over temperature condition will shut down

the MIC2033 switch and the fault status flag will go

active (assert low). After the switch cools down, it will

turn on again. The MIC2033 power dissipation can be

maximized by either lowering the thermal resistance on

the exposed pad (only the DFN package has an

exposed pad) on the printed circuit board, or by limiting

the maximum allowable ambient temperature.

Thermal Measurements

It is always wise to measure the IC’s case temperature

to make sure that it is within its operating limits. Although

this might seem like a very elementary task, it is very

easy to get erroneous results. The most common

mistake is to use the standard thermal couple that

comes with the thermal voltage meter. This thermal

couple wire gauge is large, typically 22 gauge, and

behaves like a heatsink, resulting in a lower case

measurement.

There are two suggested methods for measuring the IC

case temperature: a thermal couple or an infrared

thermometer. If a thermal couple is used, it must be

constructed of 36 gauge wire or higher to minimize the

wire heatsinking effect. In addition, the thermal couple tip

must be covered in either thermal grease or thermal glue

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