powered up, the high-speed comparator is enabled,

the low-power comparator is disabled, and STAT goes

high, placing the MAX975 back into high-speed mode

(Figure 2).

period required for the comparator to enter auto-

standby mode. Determine the capacitor required for a

10 x Cµs, where C is in pF. For example, connecting a

0.1µF capacitor to STO_ results in a timeout period of

1sec. The propagation delay of OUT_ when exiting auto

standby mode is equivalent to the low - power-mode

propagation delay. When STAT_ goes low, the low-

power comparator is disabled and the high-speed com-

parator is ready for operation. To bring the comparator

out of auto-standby mode without a transition occurring

on OUT_, toggle LP low-high-low. The LP pin is sensitive

to noise. If fall times larger than 10µs are expected,

bypass LP with a 0.1µF capacitor to GND. To disable

auto-standby mode, drive STO_ low or connect it to

ground. Note that driving STO_ low while in auto-

standby mode will not bring the comparator out of auto-

standby mode. Also, if driving STO_ with an open drain,

leakage must be less than 1nA. On power-up, the

device is in high-speed mode unless LP is high. The

MAX977 operates in the same manner as the MAX975.

Low-Power Mode

Driving LP high switches the MAX975/MAX977 to low-

power mode. In this mode, the supply current drops to

a maximum of 5

µA, and propagation delay increases

typically to 480ns. The high-speed comparator is dis-

abled and the low-power comparator is enabled for

continuous operation. Return to high-speed mode by

driving LP low. The LP pin is sensitive to noise. If fall

times larger than 10µs are expected, bypass LP with a

0.1µF capacitor to GND. The logic state and sink/

source capabilities of OUT_ remain unchanged in low-

power mode.

Input-Stage Circuitry

The MAX975/MAX977 input common-mode range is

rails. The output remains in the correct logic state while

one or both of the inputs are within the common-mode

range. If both input levels are out of the common-mode

range, input-stage current saturation occurs and the

output becomes unpredictable.

Single/Dual, +3V/+5V Dual-Speed

Comparators with Auto-Standby

12

______________________________________________________________________________________

DIFFERENTIAL

INPUT

VOLTAGE

OUT_

STAT_

LP

0V

300

µA

3

µA

A

Figure 2. Timing Diagram