±5V, ±12V (±15V) Dedicated

Microprocessor Voltage Monitors

_______________________________________________________________________________________

9

absolute maximum ratings have no effect on the refer-

ence. Within the absolute maximum ratings, the DIN

input has no effect on the reference.

Power-Supply Bypassing and Grounding

In high-noise environments where the voltage connected

“bounce,” causing false comparator outputs. Eliminate

this problem using Figure 8’s RC bypass network.

Although bypassing the reference may appear to help,

Figure 8’s solution is recommended; bypassing the ref-

erence reduces its voltage change, but doing so caus-

es a time delay prior to the reference voltage returning

to its correct level.

Eliminating Output Oscillation when

Using the Auxiliary Comparator

Although hysteresis is built into the auxiliary comparator,

output oscillation problems are still possible. Oscillation

can occur when a comparator’s output couples back to

its inverting input through stray board capacitance.

Make sure the board trace leading from the comparator

output does not pass near its inverting input (or vice

versa). Also, reducing the resistance connected to DIN

reduces its susceptibility to picking up output signals. In

most cases, using input resistor values on the order of

100k

Ω creates no problem. Since using lower resistor

values increases the supply current, another approach

is to bypass the input resistors as shown in Figure 9,

although this slows the circuit’s response. When much

larger valued input resistors are used, high valued resis-

tors on the output should be used.

When DOUT is required to sink larger currents (i.e.,

when smaller pull-up resistor values are used), oscilla-

tion problems are more likely to occur. To minimize

power consumption and to optimize stability, use the

largest value pull-up resistor feasible for the output

drive required. When lower pull-up resistor values are

used, lower values for the resistors connected to the

inputs can help alleviate oscillation problems.

MAX8215

MAX8216

14

8

PGND

0.1

µF

OUT1

DOUT

7

13

9

RESET

3

2

GND

+5V

DIN

+5V

680k

680k

1

µF

1k

Figure 7. Microprocessor Reset Circuit Monitoring Its Own

Supply Voltage

MAX8215

MAX8216

13

OUT1

14

V+

1k

0.1

µF

Figure 8. Alternate Bypass Scheme

MAX8215

MAX8216

9

DOUT

7

DIN

Figure 9. Alternative Means for Reducing Impedance Level

Seen at DIN