MIC2033 datasheet(13/28 Pages) MICROCHIP

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DS20005539C-page 13

MIC2033

4.0

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.

4.1

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 0.1 µF.

4.2

Input Capacitor

A 1 µF to 100 µF 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 or 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.

4.3

Output Capacitor

The output capacitor type and placement criteria are

the same as the input capacitor.

The exact amount of capacitance depends upon the

specific application. For example, USB applications will

typically use 150 µF, whereas local consumers, such

as microcontrollers, may require as little as 1 µF.

Care must be taken when choosing the output

capacitance for inductive loads. Without sufficient

capacitance or clamping devices, sudden disconnects

or shorts on VOUT can result in stresses beyond the

device's absolute maximum ratings, even for short

cables, which will damage the device.

4.4

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.

Care should be taken to ensure that the EN pin does

not exceed VIN by more than 500 mV at any time. This

includes at power-up and during load transients.

Whenever possible, it is recommended to tie EN to VIN

through a pull-up resistor and use an open-drain or

open-collector device to change the state.

4.5

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

10 µs to short-circuits to limit the output current and

also provides an output fault flag that will assert (low)

for an overcurrent condition that lasts longer than

32 ms.

4.6

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 overtemperature threshold. If this

occurs, the overtemperature 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.

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