January 2005

11

M9999-012004

MIC2040/2041

Micrel

Functional Description

The MIC2040 and MIC2041 are high-side N-Channel switches

equipped with programmable current limit up to 1.5A for use

in general purpose power distribution applications. The

switches, available with active-high or active-low enable

inputs, operate down to 0.8V and provide circuit protection via

thermal shutdown and an optional output latch during

overcurrent conditions.

Input and Output

VBIAS supplies power to the internal circuitry of the switch

and must be present for the switch to operate. VIN is con-

nected to the drain of the output MOSFET and sources power

to the switched load. VIN must be less than or equal to VBIAS.

VOUT is the source terminal of the output MOSFET and

attaches to the load. In a typical circuit, current flows from VIN

to VOUT toward the load. If VOUT is greater than VIN, current

will flow from VOUT to VIN since the switch is bi-directional

when the 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 MIC2040/41 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, VIN, and prevents the output

MOSFET from turning on until VIN exceeds a predetermined

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.”

Programmable Current Limit

The MIC2040/41 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 MIC2040/41 will limit from 0.25A to 1.5A with a set

point accuracy of ±18%. In programming the nominal current

limit, the value of R

equation:

R

CLF

I

340A

I

SET

LIM

LIM

==

× Ω

()

(1)

And given the ±18% tolerance of the current limit factor (CLF),

the external resistor is bound by:

(2)

The graph below (Figure 3) displays the current limit factor

characteristic over the full temperature and voltage range

indicated on the graph. This curve 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

= 340Ω), the low and high current limit settings for the

MIC2040/41 would be approximately 0.82A and 1.18A, re-

spectively, as shown on the graph using the 340Ω reference.

The MIC2041 is equipped with an internal circuit breaker for

overcurrent protection. During an overcurrent event which

exceeds the flag delay, the /FAULT output is asserted and the

MIC2041 latches the output off. Once the overcurrent load is

removed, the output automatically resets.

0

0.25

0.5

0.75

1

1.25

1.5

1.75

2

2.25

2.5

R

Current Limit vs. R

SET

CLF (LO)

V

–40°C to +85°C

CLF (HI)

Figure 3. Current Limit Factor