Micrel, Inc.

MIC845

July 2005

6

M9999-070505

(408) 955-1690

Application Information

Output

The MIC845N output is an open-drain MOSFET, so

most applications will require a pull-up resistor. It is

recommended that the value of this resistor not

exceed 470kΩ, otherwise PCB leakages may begin

to dominate and give a false output indication.

The output of “N” type devices may be pulled up as

high as 6V regardless of the IC’s supply voltage,

without damage to the IC.

The “H” and “L” versions of MIC845 have push-pull

output stages, no pull-up resistors are required. The

maximum output voltage of the “H” and “L” versions

Input

MIC845 has been designed to present an almost

infinite input resistance at its INP pin making it ideal

for monitoring lithium coin cell and back-up batteries.

In applications where the ‘battery low’ voltage is

2.55V, MIC845’s INP pin may be tied directly to the

cell’s positive terminal without any additional

circuitry.

MIC845’s input may be subjected to voltages as high

as 6V, steady-state, without any adverse effects,

regardless of the IC’s supply voltage. This applies

even if the supply voltage is zero. This permits a

situation wherein the IC’s supply is turned off, but an

input voltage is still present. Under such conditions,

circuitry internal to MIC845.

Input Transients

MIC845 is inherently immune to very short

negative-going “glitches.” Very brief transients may

As shown in the figure below, the narrower the

transient, the deeper the threshold overdrive that will

be ignored by the MIC845. The graph represents the

typical allowable transient duration for a given

amount of threshold overdrive that will not generate

an output.

0

2

4

6

8

10

12

14

16

0

200

400

600

800 1000

COMPARATOR OVERDRIVE

Input Transient

Response