MAX837 View Datasheet(PDF) - Maxim Integrated

Part Name

Description

Manufacturer

MAX837

4-Pin Micropower Voltage Monitors

Maxim Integrated 

4-Pin Micropower Voltage Monitors

_____________________________Typical Operating Characteristics (continued)

(VCC = +5V, RLOAD = 1MΩ, RPULLUP = 10kΩ (MAX836 only), TA = +25°C, unless otherwise noted.)

VCC FALLING PROPAGATION DELAY

vs. TEMPERATURE

160

1mV/μs

140

VTRIP = 4.63V

120

10mV/μs

100

80

VTRIP = 3.0V

VTRIP = 4.63V

60

VTRIP = 3.0V

40

-60 -40 -20 0 20 40 60

TEMPERATURE (°C)

80 100

1800

1600

1400

1200

1000

800

600

400

200

0

2

OUT RISE/FALL-TIME

vs. SUPPLY VOLTAGE

RISE TIME

MAX837 ONLY

FALL TIME

3 4 5 6 7 8 9 10 11 12

VCC (V)

_____________________Pin Description

PIN NAME

FUNCTION

1

GND System Ground

2

VCC

System Supply Input

Noninverting Input to the Comparator.

3

IN

The inverting input connects to the

internal 1.204V bandgap reference.

4

OUT

Open-Drain (MAX836) or

Push-Pull (MAX837) Output

GND

OUT

MAX836

VCC

RPULLUP

VCC

0.1μF

VCC

IN

VTRIP

=

(1.204)

R1

+ R2

R2

R1

R2

NOTE: UNITS ARE OHMS AND VOLTS

Figure 1. Programming the Trip Voltage, VTRIP

Detailed Description

The MAX836/MAX837 micropower voltage monitors

contain a 1.204V precision bandgap reference and a

comparator (see the Typical Operating Circuit). The

only difference between the two parts is the structure of

the comparator output driver. The MAX836 has an

open-drain n-channel output driver that can be pulled

up to a voltage higher than VCC, but under 11V. The

MAX837’s output is push-pull, and can both source

and sink current.

Programming the Trip Voltage

Two external resistors set the trip voltage, VTRIP (Figure 1).

VTRIP is the point at which the applied voltage (typically

VCC) toggles OUT. The MAX836/MAX837’s high input

impedance allows large-value resistors without compro-

mising trip-voltage accuracy. To minimize current con-

sumption, select a value for R2 between 500kΩ and

1MΩ, then calculate R1 as follows:

R1

=

R2

⎛

⎝⎜

VTRIP

VTH

⎞

- 1⎠⎟

where VTRIP = desired trip voltage (in volts), VTH =

threshold trip voltage (1.204V).

Applications Information

Adding Hysteresis

Hysteresis adds noise immunity to the MAX836/MAX837

and prevents repeated triggering when VIN is near the

threshold trip voltage. Figure 2 shows how to add hys-

teresis to the comparator. The technique is similar for

4 _______________________________________________________________________________________

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