January 2005

11

M0512-112603

MIC2042/2043

Micrel

Functional Description

The MIC2042 and MIC2043 are high-side N-Channel switches

equipped with programmable current limit up to 3A for use in

general purpose power distribution applications. The switches,

available with active-high or active-low enable inputs, provide

output slew-rate control and circuit protection via thermal

shutdown and an optional output latch during overcurrent

conditions.

Input and Output

V

must be present for the switch to operate. V

the drain of the output MOSFET and sources power to the

switched load. V

is the source terminal of the output MOSFET and attaches to

the load. In a typical circuit, current flows from V

toward the load. If V

from V

device is enabled. When disabled (OFF), the switch will block

current flow from either direction.

Enable Input

Enable, the ON/OFF control for the output switch, is a digital

input available as an active-high (–1) or active-low (–2)

signal. The EN pin, referenced to approximately 0.5 × VBIAS,

must be driven to a clearly defined logic high or logic low.

Failure to observe this requirement, or allowing EN to float,

will cause the MIC2042/43 to exhibit unpredictable behavior.

EN should not be allowed to go negative with respect to

ground, nor allowed to exceed VBIAS. Failure to adhere to

these conditions may result in damage to the device.

Undervoltage Lockout

When the switch is enabled, undervoltage lockout (UVLO)

monitors the input voltage, V

MOSFET from turning on until V

level, nominally set at 1.45V. The UVLO threshold is adjust-

able and can be varied by applying an external resistor divider

to the UVLOIN pin from VIN to GND. The resistive divider

network is required when the input voltage is below 1.5V. The

UVLO threshold is internally preset to 1.45V if the UVLOIN

pin is left open. See “Applications Information” section.

Programmable Current Limit

The MIC2042/43 is designed to prevent damage to the

external load by limiting the maximum amount of current it

can draw. The current limit is programmed by an external

resistor (R

active when the output voltage is at least 200mV below the

voltage at the input to the device. The limiting current value

is defined by the current limit factor (CLF) divided by R

and the MIC2042/43 will limit from 0.5A to 3A with a set point

accuracy of ±22%. In programming the nominal current limit,

the value of R

R

CLF

I

390A

I

SET

LIMIT

LIMIT

==

× Ω

()

(1)

And given the ±22% tolerance of the current limit factor (CLF),

the external resistor is bound by:

(2)

The graphs below (Figure 3) display the current limit factor

characteristic over the full temperature range at the indicated

voltage. These curves can be used as a point of reference in

determining the maximum variation in the device’s current

limit over the full temperature range. For example: With

V

(R

MIC2042/43 would be 1.66A and 2.34A, respectively, as

shown on the 3V graph using the 192Ω reference point.

When current limiting occurs, the MIC2042 and MIC2043

respond differently. Upon first reaching the limiting current

both devices restrict current flow, allowing the load voltage to

drop below V

ceeds 200mV, then a fault condition is declared and the fault

delay timer is started. If the fault condition persists longer than

the delay period, typically 28ms, then the /FAULT output

asserts low. At this point, the MIC2042 will continue to supply

current to the load at the limiting value (I

MIC2043 will latch off its output.

0

0.5

1

1.5

2

2.5

3

3.5

4

0 120 240 360 480 600 720 840 960

R

Current Limit

vs. R

SET

–40°C to +85°C

V

CLF (LO)

CLF (HI)

0

0.5

1

1.5

2

2.5

3

3.5

4

0 120 240 360 480 600 720 840 960

R

Current Limit

vs. R

SET

–40°C to +85°C

V

CLF (LO)

CLF (HI)

0

0.5

1

1.5

2

2.5

3

3.5

4

0 120 240 360 480 600 720 840 960

R

Current Limit

vs. R

SET

–40°C to +85°C

V

CLF (LO)

CLF (HI)

Figure 3. Current Limit Factor