MAX6412(2005) 데이터 시트보기 (PDF) - Maxim Integrated

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MAX6412
(Rev.:2005)

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

Maxim Integrated 

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

with Capacitor-Adjustable Reset Timeout Delay

Use the following formula to calculate the externally

monitored voltage (VMON_TH):

VMON_TH = VRST ✕ (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 cur-

rent consumption due to low leakage currents. Set R2

to some conveniently high value (1MΩ, for example)

and calculate R1 based on the desired monitored volt-

age, 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 man-

ual reset function (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–

GND MAX6420

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 adjustable

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

GND MAX6416

MAX6417

SRT

VMON_TH = 1.26 x (R1 + R2) / R2

R1

RESET IN

VCC

R2

MAX6415

GND MAX6416

MAX6417

SRT

Figure 1. Calculating the Monitored Threshold Voltage (VMON_TH)

Figure 3. Monitoring External Voltages

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