MAX6720AUTRDD4+T Maxim Integrated, MAX6720AUTRDD4+T Datasheet - Page 11

• Manufacturer Part Number: MAX6720AUTRDD4+T
• Description: Supervisory Circuits
• Manufacturer: Maxim Integrated
• Series: MAX6715A, MAX6716A, MAX6717A, MAX6718A, MAX6719A, MAX6720A, MAX6721A, MAX6722A, MAX6723A, MAX6724A, MAX6725A, MAX6726A, MAX6727A, MAX6728A, MAX6729A, MAX6797Ar

Specifications of MAX6720AUTRDD4+T

• Number Of Voltages Monitored: 3
• Monitored Voltage: 1.8 V to 5 V, 0.9 V to 3.3 V
• Undervoltage Threshold: 2.55 V, 0.765 V, Adjustable
• Overvoltage Threshold: 2.7 V, 0.81 V, Adjustable
• Output Type: Active Low, Push-Pull
• Manual Reset: Resettable
• Watchdog: No Watchdog
• Battery Backup Switching: No Backup
• Power-up Reset Delay (typ): 2240 ms
• Supply Voltage - Max: 5.5 V
• Maximum Operating Temperature: + 125 C
• Mounting Style: SMD/SMT
• Package / Case: SOT-23
• Chip Enable Signals: No
• Maximum Power Dissipation: 696 mW
• Minimum Operating Temperature: - 40 C
• Power Fail Detection: No
• Supply Current (typ): 15 uA
• Supply Voltage - Min: 0.8 V

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.
PFI is the noninverting input to a comparator. If PFI is
less than V
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 V
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 V
Figure 2. Normal Watchdog Startup Sequence
WDI
V
RST
CC
PFI
(626.5mV), PFO goes low. Common uses
V
Dual/Triple, Ultra-Low-Voltage, SOT23 µP
TH
______________________________________________________________________________________
t
WDI-NORMAL
t
1.12s MAX
RP
t
WDI-STARTUP
35s MAX
Power-Fail Comparator
1.12s MAX
CC
1 if unused.
CC
1 or V
CC
2 by
The MAX6715A–MAX6729A/MAX6797A are guaranteed
to operate properly down to V
that require valid reset levels down to V
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 V
old. For most applications, 100kΩ is adequate. This con-
figuration does not work for the open-drain outputs of the
M A X 6 7 1 5 A / M A X 6 7 1 7 A / M A X 6 7 1 9 A / M A X 6 7 2 1 A /
MAX6723A/MAX6725A/MAX6727A/MAX6728A. For push-
pull, active-high RST output connect the external resistor
as a pullup from RST to V
Figure 3. Using Power-Fail Input to Monitor an Additional
Power-Supply a) V
V
V
V
CC
IN
IN
A)
B)
R1
R2
R1
R2
Supervisory Circuits
PFI
PFI
MAX6728A/
MAX6729A/
MAX6728A/
MAX6729A/
MAX6797A
MAX6797A
GND
GND
IN
Ensuring a Valid Reset Output
is Positive b) V
PFO
PFO
CC
1.
CC
CC
V
is above the reset thresh-
V
IN
PFI
TRIP
Down to V
= 0.8V. In applications
V
is Negative
= 626.5mV
TRIP
= R2 (V
= V
[
PFI
PFI
CC
(
)
R1 + R2
(
R2
R1
1
= 0V, use a
+
CC
)
R2
1
)
-
= 0V
V
R1
CC
11
]