January 2000

5

MIC833

MIC833

Micrel

drain to 3.1V. Using 3.1V for the V

calculation of the two remaining resistor values.

V

3.1V

1.24

1M

R2

344k

Ω

+









R2

56k

=Ω

1M

R2 R3

R1

Ω−

−

R1 600k

=Ω

The accuracy of the resistors can be chosen based upon the

accuracy required by the system.

The inputs may be subjected to voltages as high as 6V steady

state without adverse effects of any kind, regardless of the IC

supply voltage. This applys even if the supply voltage is zero.

This permits the situation in which the IC supply is turned off,

but voltage is still present on the inputs. See “Electrical

Characteritics.”

Input Transients

The MIC833 is inherently immune to very short negative-

going “glitches.” Very brief transients may exceed the V

IN(lo)

threshold without tripping the output.

As shown in Figure 2, the narrower the transient, the deeper

the threshold overdrive that will be ignored by the MIC833.

The graph represents the typical allowable transient duration

for a given amount of threshold overdrive that will not toggle

the output.

0

20

40

60

80

100

120

140

1

10

100

1000

RESET COMP. OVERDRIVE, V

Input Transient

Response

Figure 2. Input Transient Response

Initialization Behavior

When the MIC833 is powered up, the comparators and latch

become active before the reference voltage reaches its final

value. In most applications, this presents no problems. How-

ever, the user should be aware of this: when applying power

to the part, if the input voltage is

between the two thresholds,

the output of the part will be

high because input HTH will have

been higher than the 1.24V reference during initialization.

It is not very likely the part would be powered up in this state;

it is more likely the same power supply will power the part and

develop its inputs. However, if the above-described condition

should occur, the next HTH threshold crossing would

not be

processed; that is, the latch would have been already set. The

next valid input condition would have to be a crossing of the

LTH threshold, which resets the latch, after which “normal”

operation is restored.

Applications Information

Output

Since the MIC833 output is an open-drain MOSFET, most

applications will require a pull-up resistor. The value of the

resistor should not be too large or leakage effects may

dominate. 470k

Ω is the maximum recommended value. Note

that the output may be pulled up as high as 6V regardless of

IC supply voltage. See “Electrical Characteristics.”

Programming the Thresholds

The low-voltage threshold is calculated using:

VV

R1 R2 R3

R2 R3

IN(lo)

REF

=

++

+









The high-voltage threshold is calculated using:

VV

R1 R2 R3

R3

IN(hi)

REF

=

++









where, for both equations:

V

1.240V

In order to provide the additional criteria needed to solve for

the resistor values, the resistors can be selected such that

they have a given total value, that is, R1 + R2 + R3 = R

A value such as 1M

Ω for R

because it draws minimum current but has no significant

effect on accuracy.

When working with large resistors, a small amount of leakage

current can cause voltage offsets that degrade system accu-

racy. The maximum recommended total resistance from V

IN

to ground is 3M

Ω.

HTH

OUT

VDD

LTH

GND

MIC833

604k

1%

56k

1%

340k

1%

470k

R1

R2

R3

5

3

1

4

2

Figure 1. Example Circuit

Once the desired trip points are determined, set the V

IN(hi)

threshold first.

For example, use a total of 1M

Ω = R1 + R2 + R3. For a typical

single-cell lithium ion battery, 3.6V is a good “high threshold”

because at 3.6V the battery is moderately charged. Solving

for R3:

V

3.6V

1.24

1M

R3

Ω









R3

344k

=Ω

Once R3 is determined, the equation for V

to determine R2. A single lithium-ion cell, for example, should

not be discharged below 2.5V. Many applications limit the