MAX6412 데이터 시트보기 (PDF) - Maxim Integrated

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MAX6412

Low-Power, Single/Dual-Voltage μP Reset Circuits with Capacitor-Adjustable Reset Timeout Delay

Maxim Integrated 

MAX6412–MAX6420

Low-Power, Single/Dual-Voltage μP Reset Circuits

with Capacitor-Adjustable Reset Timeout Delay

Use the following formula to calculate the externally moni-

tored voltage (VMON_TH):

VMON_TH = VRST x (R1 + R2)/R2

where VMON_TH is the desired reset threshold voltage

and VRST is the reset input threshold (1.26V). Resistors

R1 and R2 can have very high values to minimize current

consumption due to low leakage currents. Set R2 to some

conveniently high value (1MΩ, for example) and calculate

R1 based on the desired monitored voltage, using the

following formula:

R1 = R2 x (VMON_TH/VRST - 1) (Ω)

Manual Reset Input

(MAX6412/MAX6413/MAX6414)

Many μP-based products require manual reset capabil-

ity, allowing the operator, a technician, or external logic

circuitry to initiate a reset. A logic low on MR asserts reset.

Reset remains asserted while MR is low and for the reset

timeout period after MR returns high.

The MR has an internal 20kΩ pullup resistor so it can be

left open if not used. Connect a normally open momentary

switch from MR to ground to create a manual reset func-

tion (external debounce circuitry is not required for long

reset timeout periods).

A manual reset option can easily be implemented with

the MAX6415–MAX6420 by connecting a normally open

momentary switch in parallel with R2 (Figure 2). When

the switch is closed, the voltage on RESET IN goes to

zero, initiating a reset. Similar to the MAX6412/MAX6413/

MAX6414 manual reset, reset remains asserted while the

switch is closed and for the reset timeout period after the

switch is opened.

VMON_TH

VCC

R1

RESET IN

VCC

R2

MAX6415

MAX6420

GND

SRT

Figure 2. Adding an External Manual Reset Function to the

MAX6415–MAX6420

Monitoring Voltages Other than VCC

(MAX6415/MAX6416/MAX6417)

The MAX6415/MAX6416/MAX6417 contain an adjust-

able reset threshold input. These devices can be used

to monitor voltages other than VCC. Calculate VMON_TH

as shown in the Reset Threshold section. (See Figure 3.)

VMON_TH

VCC

R1

RESET IN

VCC

R2

MAX6415

MAX6416

GND MAX6417

SRT

VMON_TH = 1.26 x (R1 + R2)/R2

R1

RESET IN

VCC

R2

MAX6415

MAX6416

GND MAX6417

SRT

Figure 1. Calculating the Monitored Threshold Voltage (VMON_TH)

Figure 3. Monitoring External Voltages

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