General Description
The MAX706P/R/S/T, MAX706AP/AR/AS/AT, and
MAX708R/S/T microprocessor (µP) supervisory circuits
reduce the complexity and number of components
required to monitor +3V power-supply levels in +3V to
+5V µP systems. These devices significantly improve
system reliability and accuracy compared to separate
ICs or discrete components.
The MAX706P/R/S/T and MAX706AP/AR/AS/AT supervi-
sory circuits provide the following four functions:
1) A reset output during power-up, power-down, and
brownout conditions.
2) An independent watchdog output that goes low if the
watchdog input has not been toggled within 1.6s.
3) A 1.25V threshold detector for power-fail warning,
low-battery detection, or for monitoring a power
supply other than the main supply.
4) An active-low, manual-reset input.
The only difference between the MAX706R/AR,
MAX706S/AS, and MAX706T/AT is the reset-threshold
voltage levels, which are 2.63V, 2.93V, and 3.08V,
respectively. All have active-low reset output signals.
The MAX706P/AP are identical to the MAX706R/AR,
except the reset output signal is active-high. The watch-
dog timer function for the MAX706AP/AR/AS/AT dis-
ables when the WDI input is left open or connected to a
high-impedance state of a low-leakage tri-state output.
The MAX708R/S/T provide the same functions as the
MAX706R/S/T and MAX706AR/AS/AT except they do
not have a watchdog timer. Instead, they provide both
RESET and RESET outputs. As with the MAX706,
devices with R, S, and T suffixes have reset thresholds
of 2.63V, 2.93V, and 3.08V, respectively.
These devices are available in 8-pin SO, DIP, and
µMAX®packages and are fully specified over the oper-
ating temperature range.
Applications
Battery-Powered Equipment
Portable Instruments
Computers
Controllers
Intelligent Instruments
Critical µP Power Monitoring
Features
oµMAX Package, Small 8-Pin SO
oPrecision Supply-Voltage Monitors
2.63V (MAX706P/R, MAX706AP/AR, and MAX708R)
2.93V (MAX706S, MAX706AS, and MAX708S)
3.08V (MAX706T, MAX706AT, and MAX708T)
o200ms Reset Time Delay
oDebounced TTL/CMOS-Compatible Manual Reset
Input
o100µA Quiescent Current
oWDI Disable Feature (MAX706AP/AR/AS/AT)
oWatchdog Timer: 1.6s Timeout
oReset Output Signal:
Active-High Only (MAX706P, MAX706AP)
Active-Low Only (MAX706R/S/T, MAX706AR/AS/AT)
Active-High and Active-Low (MAX708R/S/T)
oVoltage Monitor for Power-Fail or Low-Battery
Warning
o8-Pin Surface-Mount Package
oGuaranteed RESET Assertion to VCC = 1V
MAX706P/R/S/T, MAX706AP/AR/AS/AT, MAX708R/S/T
+3V Voltage Monitoring, Low-Cost µP
Supervisory Circuits
________________________________________________________________
Maxim Integrated Products
1
Ordering Information
19-0099; Rev 5; 4/06
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
Ordering Information continued at end of data sheet.
Pin Configurations appear at end of data sheet.
µMAX is a registered trademark of Maxim Integrated Products, Inc.
PART†TEMP
RANGE
PIN-
PACKAGE
PKG
CODE
MAX706PCPA 0°C to +70°C 8 PDIP P8-1
MAX706PCSA 0°C to +70°C 8 SO S8-2
MAX706PCUA 0°C to +70°C 8 µMAX U8-1
MAX706PEPA -40°C to +85°C 8 PDIP P8-1
†
SO, µMAX, and PDIP packages are available in lead-free.
VCC
PFI
GND
MR PFO
WDO
RESET
UNREGULATED
DC
PUSHBUTTON
SWITCH
WDI I/O LINE
INTERRUPT
µP
MAX639
DC-DC
CONVERTER
+3V/+3.3V
MAX706R/S/T
MAX706AR/AS/AT
VCC
RESET
NMI
Typical Operating Circuits
Typical Operating Circuits continued at end of data sheet.
MAX706P/R/S/T, MAX706AP/AR/AS/AT, MAX708R/S/T
+3V Voltage Monitoring, Low-Cost µP
Supervisory Circuits
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(MAX70_P/R, MAX706AP/AR: VCC = 2.7V to 5.5V; MAX70_S, MAX706AS: VCC = 3.0V to 5.5V; MAX70_T, MAX706AT: VCC = 3.15V to
5.5V; TJ= TA= TMIN to TMAX, unless otherwise noted. Typical values are at TJ= TA= +25°C.) (Note 2)
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
Terminal Voltage (with respect to GND)
VCC ........................................................................-0.3V to +6V
All Other Inputs (Note 1)..........................-0.3V to (VCC + 0.3V)
Input Current
VCC ..................................................................................20mA
GND .................................................................................20mA
Output Current (all outputs) ................................................20mA
Continuous Power Dissipation (TA= +70°C)
8-Pin CERDIP (derate 8mW/°C above +70°C)..............640mW
8-Pin PDIP (derate 9.1mW/°C above +70°C).............727.3mW
8-Pin SO (derate 5.9mW/°C above +70°C)................470.6mW
8-Pin µMAX (derate 4.5mW/oC above +70°C) ..............362mW
Operating Temperature Range
MAX70_C .............................................................0°C to +70°C
MAX70_E ..........................................................-40°C to +85°C
MAX70_M .......................................................-55°C to +125°C
Junction Temperature......................................................+150°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
Note 1: The input-voltage limits on PFI, WDI, and MR can be exceeded if the input current is less than 10mA.
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
MAX70_C 1.0 5.5
Supply Voltage Range VCC MAX70_E/M 1.2 5.5 V
MAX706_C 90 200
MAX706_E/M 90 300
MAX708_C 50 200
VCC < 3.6V
MAX708_E/M 50 300
MAX706_C 135 350
MAX706_E/M 135 500
MAX708_C 65 350
Supply Current ISUPPLY
VCC < 5.5V
MAX708_E/M 65 500
µA
MAX70_P/R, MAX706AP/AR 2.55 2.63 2.70
MAX70_S, MAX706AS 2.85 2.93 3.00
Reset Threshold (Note 3)
(VCC Falling) VRST
MAX70_T, MAX706AT 3.00 3.08 3.15
V
Reset Threshold Hysteresis
(Note 3) VHYS 20 mV
MAX70_P/R, MAX706AP/AR VCC = 3.0V 140 200 280
MAX70_S, MAX706AS, VCC = 3.3V 140 200 280Reset Pulse Width (Note 3) tRST
VCC = 5V 200
ms
RESET OUTPUT
VOH VRST
(
MAX
)
< VCC < 3.6V ISOURCE = 500µA 0.8 x
VCC
VOL VRST
(
MAX
)
< VCC < 3.6V ISINK = 1.2mA 0.3
VOH 4.5V < VCC < 5.5V IRSOURCE =
800µA
VCC -
1.5
VOL 4.5V < VCC < 5.5V ISINK = 3.2mA 0.4
MAX70_C VCC = 1.0V, ISINK = 50µA 0.3
Output-Voltage High
(MAX70_R/S/T)
(MAX706AR/AS/AT)
VOL MAX70_E/M: VCC = 1.2V, ISINK = 100µA 0.3
V
MAX706P/R/S/T, MAX706AP/AR/AS/AT, MAX708R/S/T
+3V Voltage Monitoring, Low-Cost µP
Supervisory Circuits
_______________________________________________________________________________________ 3
ELECTRICAL CHARACTERISTICS (continued)
(MAX70_P/R, MAX706AP/AR: VCC = 2.7V to 5.5V; MAX70_S, MAX706AS: VCC = 3.0V to 5.5V; MAX70_T, MAX706AT: VCC = 3.15V to
5.5V; TJ= TA= TMIN to TMAX, unless otherwise noted. Typical values are at TJ= TA= +25°C.) (Note 2)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
VOH VRST
(
MAX
)
< VCC < 3.6V ISOURCE = 215µA VCC –
0.6
VOL VRST
(
MAX
)
< VCC < 3.6V ISINK = 1.2mA 0.3
VOH 4.5 < VCC < 5.5V ISOURCE = 800µA VCC -
1.5
Output-Voltage High
(MAX706P) (MAX706AP)
VOL 4.5V < VCC < 5.5V ISINK = 3.2mA 0.4
V
VOH VRST
(
MAX
)
< VCC < 3.6V ISOURCE = 500µA 0.8 x VCC
VOL VRST
(
MAX
)
< VCC < 3.6V ISINK = 500µA 0.3
VOH 4.5V < VCC < 5.5V ISOURCE = 800µA VCC -
1.5
Output-Voltage High
(MAX708_)
VOL 4.5V < VCC < 5.5V ISINK = 1.2mA 0.4
V
WATCHDOG INPUT
MAX706P/R, MAX706AP/AR, VCC = 3.0V 1.00 1.6 2.25
Watchdog Timeout Period tWD MAX706S/T, MAX706AS/AT, VCC = 3.3V 1.00 1.6 2.25 s
VIL = 0.4V VRST(MAX) < VCC
< 3.6V 100
WDI Pulse Width
(MAX706_, MAX706A_) tWP
VIH = 0.8V x VCC 4.5V < VCC <
5.5V 50
ns
VIL VRST(MAX) < VCC < 3.6V 0.6
VIH VRST(MAX) < VCC < 3.6V 0.7 x
VCC
VIL VCC = 5.0V 0.8
Watchdog Input Threshold
(MAX706_, MAX706A_)
VIH VCC = 5.0V 3.5
V
MAX706_ -1.0 +0.02 +1.0
WDI Input Current WDI = 0V or VCC MAX706A_ -5 +5 µA
MAX706P/R/S/T, MAX706AP/AR/AS/AT, MAX708R/S/T
+3V Voltage Monitoring, Low-Cost µP
Supervisory Circuits
4 _______________________________________________________________________________________
ELECTRICAL CHARACTERISTICS (continued)
(MAX70_P/R, MAX706AP/AR: VCC = 2.7V to 5.5V; MAX70_S, MAX706AS: VCC = 3.0V to 5.5V; MAX70_T, MAX706AT: VCC = 3.15V to
5.5V; TJ= TA= TMIN to TMAX, unless otherwise noted. Typical values are at TJ= TA= +25°C.) (Note 2)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
WATCHDOG OUTPUT
VOH VRST
(
MAX
)
< VCC < 3.6V ISOURCE = 500µA 0.8 x
VCC
VOL VRST
(
MAX
)
< VCC < 3.6V ISINK = 500µA 0.3
VOH 4.5V < VCC < 5.5V ISOURCE = 800µA VCC -
1.5
WDO Output Voltage
(MAX706_, MAX706A_)
VOL 4.5V < VCC < 5.5V ISINK = 1.2mA 0.4
V
MANUAL RESET INPUT
VRST(MAX) < VCC
< 3.6V 25 70 250
MR Pullup Current MR = 0
4.5V < VCC <
5.5V 100 250 600
µA
VRST(MAX) < VCC < 3.6V 500
MR Pulse Width tMR 4.5V < VCC < 5.5V 150 ns
VIL VRST(MAX) < VCC < 3.6V 0.6
VIH VRST(MAX) < VCC < 3.6V 0.7 x
VCC
VIL 4.5V < VCC < 5.5V 0.8
MR Input Threshold
VIH 4.5V < VCC < 5.5V 2.0
V
VRST(MAX) < VCC < 3.6V 750
MR to Reset Output Delay tMD 4.5V < VCC < 5.5V 250 ns
POWER-FAILURE COMPARATOR
(MAX70_P/R, MAX706AP/AR) PFI falling
VCC = 3.0V 1.2 1.25 1.3
PFI Input Threshold (MAX70_S/T, MAX706AS/AT) PFI falling,
VCC = 3.3V 1.2 1.25 1.3
V
PFI Input Current -25 +0.01 +25 nA
VOH VRST
(
MAX
)
< VCC < 3.6V ISOURCE = 500µA 0.8 x
VCC
VOL VRST
(
MAX
)
< VCC < 3.6V ISINK = 1.2mA 0.3
VOH 4.5V < VCC < 5.5V ISOURCE = 800µA VCC -
1.5
PFO Output Voltage
VOL 4.5V < VCC < 5.5V ISINK = 3.2mA 0.4
V
Note 2: All devices 100% production tested at TA= +85°C. Limits over temperature are guaranteed by design.
Note 3: Applies to both RESET in the MAX70_R/S/T and MAX706AR/AS/AT, and RESET in the MAX706P/MAX706AP.
MAX706P/R/S/T, MAX706AP/AR/AS/AT, MAX708R/S/T
+3V Voltage Monitoring, Low-Cost µP
Supervisory Circuits
_______________________________________________________________________________________
5
Typical Operating Characteristics
(TA = +25°C, unless otherwise noted.)
Typical Operating Characteristics
MAX706P/R/S/T, MAX706AP/AR/AS/AT, MAX708R/S/T
+3V Voltage Monitoring, Low-Cost µP
Supervisory Circuits
6 _______________________________________________________________________________________
Pin Description
MAX706P
MAX706AP
MAX706R/S/T,
MAX706AR/AS/AT MAX708R/S/T
SO/DIP µMAX SO/DIP µMAX SO/DIP µMAX
NAME FUNCTION
131313MR
Acti ve-Low , M anual -Reset Inp ut. P ull M R b el ow 0.6V to tr i gg er a
r eset pul se. M R i s TTL/C M OS com p ati b l e w hen V
C C
= 5V and can
b e shorted to GN D wi th a swi tch. M R i s i nter nal l y connected to a
70µA sour ce curr ent. C onnect to V
C C
or l eave unconnected .
242424V
C C S upp l y V ol tag e Inp ut
3 5 3 5 3 5 GND Ground
4 6 4 6 4 6 PFI
Adjustable Power-Fail Comparator Input. Connect PFI to a
resistive divider to set the desired PFI threshold. When PFI is
less than 1.25V, PFO goes low and sinks current; otherwise,
PFO remains high. Connect PFI to GND if not used.
575757PFO
Active-Low, Power-Fail Comparator Output. PFO asserts when
PFI is below the internal 1.25V threshold. PFO deasserts when
PFI is above the internal 1.25V threshold. Leave PFO
unconnected if not used.
6 8 6 8 — — WDI
Watchdog Input. A falling or rising transition must occur at
WDI within 1.6s to prevent WDO from asserting (see Figure 4).
The internal watchdog timer is reset to zero when reset is
asserted or when transition occurs at WDI. The watchdog
function for the MAX706P/R/S/T can not be disabled. The
watchdog timer for the MAX706AP/AR/AS/AT disables when
WDI input is left open or connected to a tri-state output in its
high-impedance state with a leakage current of less than
600nA.
7 1 — — 8 2 RESET
Active-High Reset Output. RESET remains high when VCC is
below the reset threshold or MR is held low. It remains low for
200ms after the reset conditions end (Figure 3).
8282——WDO
Active-Low Watchdog Output. WDO goes low when a
transition does not occur at WDI within 1.6s and remains low
until a transition occurs at WDI (indicating the watchdog
interrupt has been serviced). WDO also goes low when VCC
falls below the reset threshold; however, unlike the reset
output signal, WDO goes high as soon as VCC rises above
the reset threshold.
——7 171RESET
Active-Low Reset Output. RESET remains low when VCC is
below the reset threshold or MR is held low. It remains low for
200ms after the reset conditions end (Figure 3).
— — — — 6 8 N.C. No Connection. Not internally connected.
MAX706P/R/S/T, MAX706AP/AR/AS/AT, MAX708R/S/T
+3V Voltage Monitoring, Low-Cost µP
Supervisory Circuits
_______________________________________________________________________________________ 7
RESET and
RESET
Outputs
A microprocessor’s (µP’s) reset input starts in a known
state. When the µP is in an unknown state, it should be
held in reset. The MAX706P/R/S/T and the MAX706AP/
AR/AS/AT assert reset when VCC is low, preventing
code execution errors during power-up, power-down,
or brownout conditions.
On power-up once VCC reaches 1V, RESET is guaran-
teed to be logic-low and RESET is guaranteed to be
logic-high. As VCC rises, RESET and RESET remain
asserted. Once VCC exceeds the reset threshold, the
internal timer causes RESET and RESET to be
deasserted after a time equal to the reset pulse width,
which is typically 200ms (Figure 3).
If a power-fail or brownout condition occurs (i.e., VCC
drops below the reset threshold), RESET and RESET
are asserted. As long as VCC remains below the reset
threshold, the internal timer is continually reset, causing
the RESET and RESET outputs to remain asserted.
Thus, a brownout condition that interrupts a previously
initiated reset pulse causes an additional 200ms delay
from the time the latest interruption occurred. On
power-down once VCC drops below the reset threshold,
RESET and RESET are guaranteed to be asserted for
VCC ≥1V.
The MAX706P/MAX706AP provide a RESET signal, and
the MAX706R/S/T and MAX706AR/AS/AT provide a
RESET signal. The MAX708R/S/T provide both RESET
and RESET.
Watchdog Timer
The MAX706P/R/S/T and the MAX706AP/AR/AS/AT
watchdog circuit monitor the µP’s activity. If the µP
does not toggle the watchdog input (WDI) within 1.6s,
the watchdog output (WDO) goes low (Figure 4). If the
reset signal is asserted, the watchdog timer will be
reset to zero and disabled. As soon as reset is
released, the timer starts counting. WDI can detect puls-
es as narrow as 100ns with a 2.7V supply and 50ns with a
4.5V supply. The watchdog timer for the MAX706P/R/S/T
cannot be disabled. The watchdog timer for the
MAX706AP/AR/AS/AT operates similarly to the
MAX706P/R/S/T. However, the watchdog timer for the
MAX706AP/AR/AS/AT disables when the WDI input is
left open or connected to a tri-state output in its high-
impedance state and with a leakage current of less
than 600nA. The watchdog timer can be disabled any-
time, provided WDO is not asserted.
RESET
GENERATOR
VCC
70µA
8
7RESET
RESET
5PFO
GND
3
1.25V
2.63V MAX708R
2.93V MAX708S
3.08V MAX708T
1
MR
2
VCC
4
PFI
MAX708R/S/T
Figure 1. MAX706_ Functional Diagram Figure 2. MAX708_ Functional Diagram
WATCHDOG
TRANSITION
DETECTOR
WATCHDOG
TIMER
TIMEBASE FOR
RESET AND
WATCHDOG
RESET
GENERATOR
VCC
70µA
8WDO
7RESET
(RESET)
5PFO
GND
3
1.25V
2.63V MAX706P/R
2.93V MAX706S
3.08V MAX706T
( ) ARE FOR MAX706P/AP.
6
WDI
1
MR
2
VCC
4
PFI
MAX706P/R/S/T
MAX706AP/AR/AS/AT
MAX706P/R/S/T, MAX706AP/AR/AS/AT, MAX708R/S/T
+3V Voltage Monitoring, Low-Cost µP
Supervisory Circuits
8 _______________________________________________________________________________________
WDO can be connected to the nonmaskable interrupt
(NMI) input of a µP. When VCC drops below the reset
threshold, WDO immediately goes low, even if the
watchdog timer has not timed out (Figure 3). Normally,
this would trigger an NMI, but since reset is asserted
simultaneously, the NMI is overridden. The WDO
should not be connected to RESET directly. Instead,
connect WDO to MR to generate a reset pulse when it
times out.
Manual Reset
The manual reset (MR) input allows RESET and RESET
to be activated by a pushbutton switch. The switch is
effectively debounced by the 140ms minimum reset
pulse width. MR can be driven by an external logic line
since it is TTL/CMOS compatible. The minimum MR
input pulse width is 500ns when VCC = +3V and 150ns
when VCC = +5V. Leave MR unconnected or connect
to VCC when not used.
Power-Fail Comparator
The power-fail comparator can be used for various pur-
poses because its output and noninverting input are
not internally connected. The inverting input is internally
connected to a 1.25V reference. The power-fail com-
parator has 10mV of hysteresis, which prevents repeat-
ed triggering of the power-fail output (PFO).
tRST tRST
+3.3V
0V
+3.3V
+1V
0V
RESET
RESET
WDO*
+3.3V
0V
MR*
tMR
*NOTE: MR EXTERNALLY DRIVEN LOW.
WDO TIMING SHOWN FOR MAX706P/R/S/T.
+3.3V
0V
VCC VRST VRST
tMD
tWP
tWD tWD tWD
+3V/+3.3V
0V
WDI
+3V/+3.3V
0V
WDO
+3V/+3.3V
0V
RESET
tRST
RESET EXTERNALLY
TRIGGERED BY MR
MAX706_
MAX708R/S/T
RESET
(RESET)
130kΩ
1%
PARAMETER MIN TYP MAX UNIT
+12V RESET
THRESHOLD AT +25°C10.24 10.87 11.50 V
1MΩ
1%
+3V/+3.3V
+12V
VCC
PFI
( ) ARE FOR MAX706P/AP
GND
MR
PFO
TO µP
MAX706R/S/T
MAX708R/S/T
MAX706AR/AS/AT
RESET
R1
Figure 4. MAX706AP/AR/AS/AT Watchdog Timing
Figure 3. RESET, RESET, MR, and WDO Timing
Figure 5. Monitoring Both +3V/+3.3V and +12V
Figure 6. RESET Valid to GND Circuit
MAX706P/R/S/T, MAX706AP/AR/AS/AT, MAX708R/S/T
+3V Voltage Monitoring, Low-Cost µP
Supervisory Circuits
_______________________________________________________________________________________ 9
To build an early-warning power-failure circuit, use the
power-fail comparator input (PFI) to monitor the unregu-
lated DC supply voltage (see the
Typical Operating
Circuits
). Connect the PFI to a resistive-divider network
such that the voltage at PFI falls below 1.25V just
before the regulator drops out. Use PFO to interrupt the
µP so it can prepare for an orderly power-down.
Regulated and unregulated voltages can be monitored
by simply adjusting the PFI resistive-divider network
values to the appropriate ratio. In addition, the reset
signal can be asserted at voltages other that VCC reset
threshold, as shown in Figure 5. Connect PFO to MR to
initiate a reset pulse when the 12V supply drops below
a user-specified threshold (11V in this example) or
when VCC falls below the reset threshold.
Operation with +3V and +5V Supplies
The MAX706P/R/S/T, the MAX706AP/AR/AS/AT, and the
MAX708R/S/T provide voltage monitoring at the reset
threshold (2.63V to 3.08V) when powered from either
+3V or +5V. These devices are ideal in portable-instru-
ment applications where power can be supplied from
either a +3V battery or an AC-DC wall adapter that gen-
erates +5V (a +5V supply allows a µP or a microcon-
troller to run faster than a +3V supply). With a +3V
supply, these ICs consume less power, but output drive
capability is reduced, the MR to RESET delay time
increases, and the MR minimum pulse width increases.
The
Electrical Characteristics
table provides specifica-
tions for operation with both +3V and +5V supplies.
Ensuring a Valid
RESET
Output Down to
VCC = 0V
When VCC falls below 1V, the MAX706R/S/T,
MAX706AR/AS/AT, and MAX708R/S/T RESET output no
longer sinks current; it becomes an open circuit. High-
impedance, CMOS logic inputs can drift to undeter-
mined voltages if left as open circuit. If a pulldown
resistor is added to the RESET pin , as shown in Figure
6, any stray charge or leakage current will flow to
ground, holding RESET low. Resistor value R is not criti-
cal, but it should not load RESET and should be small
enough to pull RESET and the input it is driving to
ground. 100kΩis suggested for R1.
Applications Information
Adding Hysteresis to the Power-Fail
Comparator
Hysteresis adds a noise margin to the power-fail com-
parator and prevents repeated triggering of the PFO
when VIN is near the power-fail comparator trip point.
Figure 7 shows how to add hysteresis to the power-fail
comparator. Select the ratio of R1 and R2 such that PFI
MAX706_
MAX708R/S/T
VCC
GND
PFI
*OPTIONAL
R2
R3
R1
VIN +3V/+3.3V
C1*
TO µP
PFO
VTRIP = 1.25 (R1 + R2)
R2
PFO
+3V/+3.3V
0V
0V VH
VH = 1.25 (1 + R3 + R2 R1) VL = 1.25 + R1 1.25 - VCC - 1.25
R2 × R3 R2 R3
VTRIP
VIN
VL
MAX706_
MAX708R/S/T
VCC
GND
PFI
R2
R1
+3V/+3.3V
PFO
PFO
+3V/+3.3V
0V
NOTE: VTRIP IS NEGATIVE.
0V
VTRIP
V-
VCC - 1.25 = 1.25 - VTRIP
R1 R2
V-
Figure 8. Monitoring a Negative Voltage
Figure 7. Adding Hysteresis to the Power-Fail Comparator
MAX706P/R/S/T, MAX706AP/AR/AS/AT, MAX708R/S/T
+3V Voltage Monitoring, Low-Cost µP
Supervisory Circuits
10 ______________________________________________________________________________________
Ordering Information (continued)
Chip Information
PROCESS: CMOS
sees 1.25V when VIN falls to the desired trip point
(VTRIP). Resistor R3 adds hysteresis. R3 will typically
be an order of magnitude greater than R1 and R2. The
current through R1 and R2 should be at least 1µA to
ensure that the 25nA (max) PFI input current does not
shift the trip point significantly. R3 should be larger than
10kΩto prevent it from loading down the PFO pin.
Capacitor C1 adds noise rejection.
Monitoring a Negative Voltage
The power-fail comparator can be used to monitor a
negative supply voltage using the circuit of Figure 8.
When the negative supply is valid, PFO is low. When
the negative supply voltage drops, PFO goes high. This
circuit’s accuracy is affected by the PFI threshold toler-
ance, the VCC voltage, and resistors R1 and R2.
Bypassing VCC
For noisy systems, bypass VCC with a 0.1µF capacitor
to GND.
PART†TEMP
RANGE
PIN-
PACKAGE
PKG
CODE
MAX706PEUA -40°C to +85°C 8 µMAX U8-1
MAX706PMJA -55°C to +125°C 8 CERDIP* J8-2
MAX706RCPA 0°C to +70°C 8 Plastic Dip P8-1
MAX706RCSA 0°C to +70°C 8 SO S8-2
MAX706RCUA 0°C to +70°C 8 µMAX U8-1
MAX706REPA -40°C to +85°C 8 Plastic Dip P8-1
MAX706RESA -40°C to +85°C 8 SO S8-2
MAX706REUA -40°C to +85°C 8 µMAX U8-1
MAX706RMJA -55°C to +125°C 8 CERDIP* J8-2
MAX706SCPA 0°C to +70°C 8 Plastic Dip P8-1
MAX706SCSA 0°C to +70°C 8 SO S8-2
MAX706SCUA 0°C to +70°C 8 µMAX U8-1
MAX706SEPA -40°C to +85°C 8 Plastic Dip P8-1
MAX706SESA -40°C to +85°C 8 SO S8-2
MAX706SEUA -40°C to +85°C 8 µMAX U8-1
MAX706SMJA -55°C to +125°C 8 CERDIP* J8-2
MAX706TCPA 0°C to +70°C 8 Plastic Dip P8-1
MAX706TCSA 0°C to +70°C 8 SO S8-2
MAX706TCUA 0°C to +70°C 8 µMAX U8-1
MAX706TEPA -40°C to +85°C 8 Plastic Dip P8-1
MAX706TESA -40°C to +85°C 8 SO S8-2
MAX706TEUA -40°C to +85°C 8 µMAX U8-1
MAX706TMJA -55°C to +125°C 8 CERDIP* J8-2
M A X7 0 6 A PE P A -40°C to +85°C 8 Plastic Dip P8-1
M AX 706AP E S A -40°C to +85°C 8 SO S8-2
M AX 706AP E U A -40°C to +85°C 8 µMAX U8-1
MAX706AREPA -40°C to +85°C 8 Plastic Dip P8-1
MAX706ARESA -40°C to +85°C 8 SO S8-2
MAX706AREUA -40°C to +85°C 8µMAX U8-1
MAX706ASEPA -40°C to +85°C 8 Plastic Dip P8-1
PART†TEMP
RANGE
PIN-
PACKAGE
PKG
CODE
MAX706ASESA -40°C to +85°C 8 SO S8-2
MAX706ASEUA -40°C to +85°C 8 µMAX U8-1
MAX706ATEPA -40°C to +85°C 8 Plastic Dip P8-1
MAX706ATESA -40°C to +85°C 8 SO S8-2
MAX706ATEUA -40°C to +85°C 8 µMAX U8-1
MAX708RCPA 0°C to +70°C 8 Plastic Dip P8-1
MAX708RCSA 0°C to +70°C 8 SO S8-2
MAX708RCUA 0°C to +70°C 8 µMAX U8-1
MAX708REPA -40°C to +85°C 8 Plastic Dip P8-1
MAX708RESA -40°C to +85°C 8 SO S8-2
MAX708REUA -40°C to +85°C 8 µMAX U8-1
MAX708RMJA -55°C to +125°C 8 CERDIP* J8-2
MAX708SCPA 0°C to +70°C 8 Plastic Dip P8-1
MAX708SCSA 0°C to +70°C 8 SO S8-2
MAX708SCUA 0°C to +70°C 8 µMAX U8-1
MAX708SEPA -40°C to +85°C 8 Plastic Dip P8-1
MAX708SESA -40°C to +85°C 8 SO S8-2
MAX708SEUA -40°C to +85°C 8 µMAX U8-1
MAX708SMJA -55°C to +125°C 8 CERDIP* J8-2
MAX708TCPA 0°C to +70°C 8 Plastic Dip P8-1
MAX708TCSA 0°C to +70°C 8 SO S8-2
MAX708TCUA 0°C to +70°C 8 µMAX U8-1
MAX708TEPA -40°C to +85°C 8 Plastic Dip P8-1
MAX708TESA -40°C to +85°C 8 SO S8-2
MAX708TEUA -40°C to +85°C 8 µMAX U8-1
MAX708TMJA -55°C to +125°C 8 CERDIP* J8-2
†
SO, µMAX, and PDIP packages are available in lead-free.
*Contact factory for availability and processing to MIL-STD-883.
MAX706P/R/S/T, MAX706AP/AR/AS/AT, MAX708R/S/T
+3V Voltage Monitoring, Low-Cost µP
Supervisory Circuits
______________________________________________________________________________________ 11
VCC
PFI
GND
MR PFO
RESET
RESET
UNREGULATED
DC
PUSHBUTTON
SWITCH
INTERRUPT
µP
MAX639
DC-DC
CONVERTER
-3V/+3.3V
MAX708R/S/T
VCC
RESET
Typical Operating Circuits
(continued)
1
2
3
4
8
7
6
5
WDO
RESET
WDI
PFO
PFI
PFI
VCC
MR
µMAX
MAX706P/R/S/T
MAX706AP/AR/
AS/AT
1
2
3
4
8
7
6
5
N.C.
GND
GND
VCC
MR
µMAX
MAX708R/S/T
( ) ARE FOR MAX706P/AP ONLY.
(RESET) RESET
PFO
RESET
TOP VIEW
1
2
3
4
8
7
6
5
WDO
RESET
WDI
WDI
PFO
PFI
GND
VCC
MR
DIP/SO
MAX706P
MAX706AP
1
2
3
4
8
7
6
5
RESET
PFO
PFI
GND
VCC
MR
DIP/SO
MAX706R/S/T
MAX706AR/AS/AT
WDO
N.C.
1
2
3
4
8
7
6
5
RESET
PFO
PFI
GND
VCC
MR
DIP/SO
MAX708R/S/T
RESET
Pin Configurations
MAX706P/R/S/T, MAX706AP/AR/AS/AT, MAX708R/S/T
+3V Voltage Monitoring, Low-Cost µP
Supervisory Circuits
12 ______________________________________________________________________________________
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information
go to www.maxim-ic.com/packages.)
CDIPS.EPS
MAX706P/R/S/T, MAX706AP/AR/AS/AT, MAX708R/S/T
+3V Voltage Monitoring, Low-Cost µP
Supervisory Circuits
______________________________________________________________________________________ 13
Package Information (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information
go to www.maxim-ic.com/packages.)
α
α
MAX706P/R/S/T, MAX706AP/AR/AS/AT, MAX708R/S/T
+3V Voltage Monitoring, Low-Cost µP
Supervisory Circuits
14 ______________________________________________________________________________________
Package Information (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information
go to www.maxim-ic.com/packages.)
MAX706P/R/S/T, MAX706AP/AR/AS/AT, MAX708R/S/T
+3V Voltage Monitoring, Low-Cost µP
Supervisory Circuits
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________
15
© 2006 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products, Inc.
Package Information (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information
go to www.maxim-ic.com/packages.)
PDIPN.EPS
