MIC2042/2043

Micrel

M0512-112603

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

(5)

To relate this to junction temperature, the following equation

can be used:

T

(6)

where T

Printed Circuit Board Hot-Plug

The MIC2042/43 are ideal inrush current limiting power

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

grated charge pump, the MIC2042/43 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.

PCB Layout Recommendations

The MIC2042 and MIC2043 have very low on-resistance,

typically 40mΩ, and the switches can provide up to 3A of

continuous output current. Under such heavy loads, the

power consumed by the devices may cause the devices to

8, 12

7

2

4

9

6

13

10,11,14

1

3

200W

C1

0.1mF

5

MIC2042-1BTS

VBIAS

VIN

EN

/FAULT

UVLOIN

SLEW

VOUT

PGREF

PWRGD

ILIM

GND

R1

47kW

R4

1%

R5

1%

0.8V @1.5A

R7

47kW

Digital

Output

Signals

C3

10mF

C2

0.1mF

0.8V

2.5V

R2

95.3kW

1%

R3

59kW

1%

R6

47kW

Note:

Undervoltage Lockout = 0.6V.

Output Power-Good = 0.7V.

Figure 4. Lower UVLO Setting

heat up considerably. The following list contains some useful

suggestions for PCB layout design of the MIC2042/43 in

order to prevent the die from overheating under normal

operating conditions:

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 MIC2042/43 IC for heat distribution.

3. Tie the common power pins (VIN = pins 8 and

12 and VOUT = pins 10, 11, 14 for the 14-pin

TSSOP, VIN = pins 5 and 7 and VOUT = pins 6

and 8 for the 8-pin SOP) together in a manner

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 2A maximum current, design traces for

2.5A capability.

4. For PCB trace width calculation, 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.