MIC2040/2041

Micrel

M9999-012004

14

January 2005

Power Dissipation

Power dissipation depends on several factors such as the

load, PCB layout, ambient temperature, and package type.

The following equations can be used to calculate power

dissipation and die temperature.

Calculation of power dissipation can be accomplished by the

following equation:

P

2

(4)

To relate this to junction temperature, the following equation

can be used:

T

(5)

where T

and R

Printed Circuit Board Hot-Plug

The MIC2040/41 are ideal inrush current limiting power

switches suitable for hot plug applications. Due to the inte-

grated charge pump, the MIC2040/41 present a high imped-

ance when in the off state and the device slowly becomes a

low impedance as it turns on. This effectively isolates power

supplies from highly capacitive loads by reducing inrush

current during hot plug events. This same feature also can be

used for soft-start requirements.

Bus-Powered Hub (USB)

Figure 5 illustrates a bus-powered hub application where the

MIC2040 provides ganged power switching to multiple down-

stream ports. A low-cost MIC5203 (SOT-143) or MIC5207

(TO-92) 3.3V low-dropout (LDO) regulator provides power

from the bus to the USB controller.

PCB Layout Recommendations

The MIC2040 and MIC2041 have very low on-resistance,

typically 50mΩ, and the switches can provide up to 1.5A of

continuous output current. Under maximum load, the power

consumed by the devices may cause the devices to heat up

considerably. The following list contains some useful sug-

gestions for PCB layout design of the MIC2040/41 in order to

prevent the die from overheating under normal operating

conditions.

7, 9

6

1

2

5

8,10

3

220Ω

Note:

BothV

BothV

I

C2

0.1µF

3.3V USB

Controller

MIC5203-3.3

ON/OFF

OC

IN

D+

D-

GND

4

MIC2040-1BM

VBIAS

VIN

EN

/FAULT

ILIM

VOUT

UVLOIN

GND

LDO

Regulator

R2

20kΩ

R1

20kΩ

(OPEN)

5V@ 1A

C1

0.1µF

Downstream port

(100mA max.)

Downstream port

(100mA max.)

Downstream port

(100mA max.)

GND

OUT

IN

C4

C3

VBUS

D+

D-

GND

Figure 5. Multi-Port Bus-Powered Hub

1. Supply additional copper area under the device

to remove heat away from the IC.

See “Application Hint 17” for a general guideline in

calculating the suggested area.

2. Provide additional pad area on the corner pins of

the MIC2040/41 IC for heat distribution.

3. Tie the common power pins (V

and V

such that the traces entering and leaving the

device have a uniform width sufficient for the

application’s current requirements plus added

margin (25% minimum recommended).

Ex: For 1A maximum current, design traces for

1.25A capability.

4. For PCB trace width calculations, there are

numerous calculator programs available on the

internet and elsewhere. As a general rule of

thumb, 15-20 mils for every 1A of current when

using 1oz. copper. However, the trace width

calculators often take into account maximum

temperature increase constraints, as well as

layer arrangement, in determining the PCB trace

widths.