MAX6723AUTWFD2-T View Datasheet(PDF) - Maxim Integrated

Part Name

Description

Manufacturer

MAX6723AUTWFD2-T

Dual/Triple, Ultra-Low-Voltage, SOT23 µP Supervisory Circuits

Maxim Integrated 

Dual/Triple, Ultra-Low-Voltage, SOT23 µP

Supervisory Circuits

The normal watchdog timeout period (1.12s min)

begins after the first transition on WDI before the con-

clusion of the long initial watchdog period (Figure 2).

During the normal operating mode, the supervisor will

issue a reset pulse for the reset timeout period if the µP

does not update the WDI with a valid transition (high-to-

low or low-to-high) within the standard timeout period

(1.12s min).

Leave WDI unconnected to disable the watchdog timer.

The WDI unconnected-state detector uses a small

(200nA typ) current source. Therefore, do not connect

WDI to anything that will source more than 50nA.

Power-Fail Comparator

PFI is the noninverting input to a comparator. If PFI is

less than VPFI (626.5mV), PFO goes low. Common uses

for the power-fail comparator include monitoring prereg-

ulated input of the power supply (such as a battery) or

providing an early power-fail warning so software can

conduct an orderly system shutdown. It can also be

used to monitor supplies other than VCC1 or VCC2 by

setting the power-fail threshold with a resistor-divider, as

shown in Figure 3. PFI is the input to the power-fail com-

parator. The typical comparator delay is 2µs from PFI to

PFO. Connect PFI to ground of VCC1 if unused.

Ensuring a Valid Reset Output

Down to VCC = 0V

The MAX6715A–MAX6729A/MAX6797A are guaranteed

to operate properly down to VCC = 0.8V. In applications

that require valid reset levels down to VCC = 0V, use a

pulldown resistor at RST to ground. The resistor value

used is not critical, but it must be large enough not to

load the reset output when VCC is above the reset thresh-

old. For most applications, 100kΩ is adequate. This con-

figuration does not work for the open-drain outputs of the

MAX6715A/MAX6717A/MAX6719A/MAX6721A/

MAX6723A/MAX6725A/MAX6727A/MAX6728A. For push-

pull, active-high RST output connect the external resistor

as a pullup from RST to VCC1.

A)

VIN

R1

R2

MAX6728A/

MAX6729A/

MAX6797A

PFI

PFO

( ) VTRIP = VPFI

R1 + R2

R2

GND

VTH

VCC

tWDI-NORMAL

1.12s MAX

tWDI-STARTUP

35s MAX

WDI

1.12s MAX

RST

tRP

B)

VCC

R1

R2

MAX6728A/

MAX6729A/

MAX6797A

PFI

PFO

VIN

GND

[ ( ) ] VTRIP = R2

(VPFI)

1+

R1

1

R2

- VCC

R1

VPFI = 626.5mV

Figure 2. Normal Watchdog Startup Sequence

Figure 3. Using Power-Fail Input to Monitor an Additional

Power-Supply a) VIN is Positive b) VIN is Negative

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