General Description
The MAX6342–MAX6345 family of microprocessor (µP)
supervisory circuits monitors power supplies in digital sys-
tems. These devices significantly improve system reliabili-
ty and accuracy compared to separate ICs or discrete
components.
The MAX6342–MAX6345 provide factory-trimmed VCC
reset threshold voltages from 2.33V to 4.63V and operate
with supply voltages between +1V and +5.5V. A +1.25V
threshold detector allows for a power-fail warning, for
low-battery detection, or for monitoring another power
supply. The MAX6342 contains an MR input and an
active-low push-pull reset. The MAX6343 and MAX6344
are identical to the MAX6342 except they provide an
active-low, open-drain reset and an active-high, push-
pull reset, respectively. The MAX6345 provides a second
reset output in place of the MR input to give it an active-
high push-pull reset and an active-low push-pull reset.
All of the devices are packaged in a miniature 6-pin
SOT23.
Applications
Portable Computers
Telecom Equipment
Networking Equipment
Portable/Battery-Powered Equipment
Multivoltage Systems
Embedded Control Systems
Features
♦Small 6-Pin SOT23 Package
♦Precision Factory-Set VCC Reset Thresholds
Between 2.33V and 4.63V
♦Guaranteed RESET Valid to VCC = +1V
♦100ms min Reset Pulse Width
♦Debounced CMOS-Compatible Manual-Reset
Input
♦Voltage Monitor for Power-Fail or Low-Battery
Warning
MAX6342–MAX6345
6-Pin µP Reset Circuit with
Power-Fail Comparator
________________________________________________________________ Maxim Integrated Products 1
GND
PFI
16
5
VCC
( ) ARE FOR MAX6344 ONLY.
TOP VIEW
2
34
RESET (RESET)
PFO
MR
MAX6342
MAX6343
MAX6344
SOT23-6
Selector Guide 1
Selector Guide 2
19-1568; Rev 2; 12/05
PART
MAX6342_UT-T
MAX6343_UT-T
MAX6344_UT-T -40°C to +125°C
-40°C to +125°C
-40°C to +125°C
TEMP RANGE PIN-PACKAGE
6 SOT23-6
6 SOT23-6
6 SOT23-6
Note: The MAX6342–MAX6345 are available with factory-set
reset thresholds from 2.33V to 4.63V (see Selector Guides 1, 2).
Insert the letter corresponding to the desired nominal reset
threshold into the blank following the part number. There is a
2500 piece order increment required for the SOT package. SOT
Top Marks table appears at end of data sheet.
Devices are available in both leaded and lead-free packaging.
Specify lead-free by replacing “-T” with “+T” when ordering.
Pin Configurations
Ordering Information
MAX6345_UT-T -40°C to +125°C 6 SOT23-6
PART PUSH-PULL
RESET OUTPUT
OPEN-DRAIN
RESET OUTPUT
PUSH-PULL RESET
OUTPUT
MAX6342 ✔— —
MAX6343 —✔—
MAX6344 — — ✔
MAX6345 ✔—✔
MANUAL-RESET
INPUT
✔
✔
✔
—
Typical Operating Circuit appears at end of data sheet.
Pin Configurations continued at end of data sheet.
SUFFIX RESET THRESHOLD (V)
L4.63
M4.38
T3.08
S2.93
R2.63
Z2.33
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.
µA
MAX6342–MAX6345
6-Pin µP Reset Circuit with
Power-Fail Comparator
2_______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VCC = +1.0V to +5.5V, TA= -40°C to +125°C, unless otherwise noted. Typical values are at TA= +25°C and VCC = +3V.) (Note 1)
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.
VCC to GND..............................................................-0.3V to +6V
RESET, RESET
(MAX6342/MAX6344/MAX6345) ......... -0.3V to (VCC + 0.3V)
RESET (MAX6343)................................................... -0.3V to +6V
MR, PFI, PFO ..............................................-0.3V to (VCC + 0.3V)
Input Current, VCC ..............................................................50mA
Output Current, RESET, RESET ..........................................50mA
Continuous Power Dissipation (TA= +70°C)
6-Pin SOT23 (derate 4mW/°C above +70°C).............320mW
Operating Temperature Range .........................-40°C to +125°C
Junction Temperature......................................................+150°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature Range (soldering, 10s)..................... +300°C
V
VCC > 1.2V, ISINK = 100µA 0.4
VOL
RESET and RESET
Outputs Drive
Capability (Note 2)
TA= -40°C to +85°C 2.25 2.38
TA= -40°C to +125°C 2.21 2.45
MAX634_Z
MAX634_S
MAX634_T
MAX634_M
TA= +25°C
TA= -40°C to +125°C
TA= -40°C to +85°C
TA= +25°C
2.50 2.76
MAX634_R
2.59 2.63 2.67
2.55 2.70
2.30 2.33 2.36
TA= -40°C to +125°C
TA= -40°C to +85°C
TA= +25°C
TA= -40°C to +125°C
2.85 3.00
2.92 3.23
2.89 2.93 2.97
2.78 3.08
TA= -40°C to +85°C
TA= +25°C
TA= -40°C to +125°C
TA= -40°C to +85°C
3.03 3.08 3.13
4.25 4.50
4.16 4.56
3.00 3.15
TA= +25°C
TA= -40°C to +125°C
TA= -40°C to +85°C
TA= +25°C
4.40 4.86
V
MAX634_L
4.56 4.63 4.70
VTH
Reset Threshold
4.50 4.75
4.31 4.38 4.45
30 60
VCC = 5.5V, TA = -40° to +125°C
VCC = 3V, TA = -40° to +125°C
VCC = 5.5V, TA = -40° to +85°C
VCC = 3V, TA = -40° to +85°C
25 50
TA= -40°C to +125°C
TA= 0°C to +70°C
VCC = VTH to (VTH - 100mV)
µANo load
CONDITIONS
µs
20
VCC to Reset Delay
25 40
ICC
Supply Current
1.2 5.5 V
1.0 5.5
VCC
Supply Voltage Range
30 50
UNITSMIN TYP MAXSYMBOLPARAMETER
VCC > 2.7V, ISINK = 1.2mA
VCC > 4.5V, ISINK = 3.2mA 0.4
0.3
V
0.8 ✕VCC
VCC > 1.2V, ISOURCE = 50µA
0.8 ✕VCC
VCC > 2.7V, ISOURCE = 500µA
(MAX6342/MAX6345 only)
0.8 ✕VCC
VCC > 4.5V, ISOURCE = 800µA
(MAX6342/MAX6345 only)
VOH
MAX6342–MAX6345
6-Pin µP Reset Circuit with
Power-Fail Comparator
_______________________________________________________________________________________ 3
ELECTRICAL CHARACTERISTICS (continued)
(VCC = +1.0V to +5.5V, TA= -40°C to +125°C, unless otherwise noted. Typical values are at TA= +25°C and VCC = +3V.) (Note 1)
Typical Operating Characteristics
(VPFI = VCC = +5V, TA= +25°C, unless otherwise noted.)
0
10
5
20
15
25
30
-40 10-15 35 60 85
SUPPLY CURRENT vs. SUPPLY VOLTAGE
AND TEMPERATURE
MAX6342-01
TEMPERATURE (°C)
SUPPLY CURRENT (µA)
VCC = 5V
VCC = 3.3V
VCC = 2.5V
VCC = 1V
0
0
1sec/div
MAX6342-02
MAX6344L/MAX6345L
RESET OUTPUT VOLTAGE
vs. SUPPLY VOLTAGE
VCC
RESET
1V/div
0
0
1sec/div
MAX6342-03
MAX6342M/MAX6345M
RESET OUTPUT VOLTAGE
vs. SUPPLY VOLTAGE
VCC
RESET
1V/div
Note 1: Overtemperature limits are guaranteed by design and not production tested.
Note 2: Apply to each part in accordance with threshold voltage, output configuration, and manual reset status selected.
Note 3: Leakage parameters are guaranteed by design and not production tested.
V
µs
3
VOVERDRIVE = 15mV
PFI to PFO Delay
5
Output source current mA
20
Output sink current
PFO Output Short-Circuit
Current
0.8 ✕VCC
VCC = 4.5V, ISOURCE = 800µAVOH
PFO Output Voltage
V
0.4
VCC = 4.5V, ISINK = 3.2mAVOL
PFO Output Voltage
PFI Input Threshold
µs
0.2
MR to Reset Delay
µs
0.1
MR Glitch Rejection
µs
1
MR Minimum Pulse Width
kΩ
60
Open-Drain RESET Output
Leakage Current (Note 3) ILKG 1µA
MR Input Low VIL 0.3 ✕VCC V
MR Input High VIH 0.7 ✕VCC V
MR Pull-Up Resistance
MAX6343 only, VCC > VTH(MAX)
PARAMETER SYMBOL MIN TYP MAX UNITSCONDITIONS
PFI Leakage Current (Note 3)
1.2 1.25 1.3
TA= -40°C to +85°C
TA= -40°C to +125°C
±0.01 ±25
TA= -40°C to +85°C
TA= -85°C to +125°C
V
1.15 1.35
nA
±100
Reset Timeout Period tRP
100 180 280 ms
TA= -40°C to +85°C
TA= -40°C to +125°C 80 360
MAX6342–MAX6345
6-Pin µP Reset Circuit with
Power-Fail Comparator
4_______________________________________________________________________________________
0
2
1
4
3
5
6
0213456
MAX6342-04
SUPPLY VOLTAGE (V)
PFO OUTPUT-VOLTAGE HIGH
vs. SUPPLY VOLTAGE
PFO (V)
RL = 10kΩ
0.20
0.30
0.35
0.25
0.45
0.40
0.50
0.55
0.60
0213456
MAX6342-05
SUPPLY VOLTAGE (V)
PFO OUTPUT-VOLTAGE LOW
vs. SUPPLY VOLTAGE
PFO (V)
RL = 1kΩ
10µs/div
MAX6342-06
MAX6344/MAX6345
RESET RESPONSE TIME
VCC
RESET
0
4V
5V
4V
2µs/div
MAX6342-07
MAX6342/MAX6345
RESET RESPONSE TIME
VCC
0
4V
5V
4V
RESET
5V
Typical Operating Characteristics (continued)
(VPFI = VCC = +5V, TA= +25°C, unless otherwise noted.)
Pin Description
MAX6344
1 1 Supply Voltage
2 2 Ground
MAX6342
3 3 Power-Fail Voltage Monitor Input. When PFI is < 1.25V, PFO
goes low. Connect PFI to GND or VCC when not used.
4 4 Power-Fail Voltage Monitor Output
FUNCTION
PIN
NAME
1
2
MAX6343
3
4
MAX6345
1
2
3
4
VCC
GND
PFI
PFO
MAX6342–MAX6345
6-Pin µP Reset Circuit with
Power-Fail Comparator
_______________________________________________________________________________________ 5
MAX6344MAX6342
— 6
Active-High Push-Pull Reset Output. It remains high for 180ms
after VCC rises above the reset threshold or MR goes from low
to high.
6 —
Active-Low Reset Output. Push-pull for MAX6342/MAX6345.
Open-drain for MAX6343. It remains low for 180ms after VCC
rises above the reset threshold or MR goes from low to high.
5 5
Manual-Reset Input. Pull low to force a reset. RESET or RESET
remains active as long as MR is low and for the reset timeout
period after MR goes high. Leave unconnected or connect to
VCC if unused.
Pin Description (continued)
MAX6343
—
6
5
MAX6345
6
5
—
RESET
RESET
MR
FUNCTION
PIN
NAME
_______________Detailed Description
Reset Output
A µP’s reset input starts the µP in a known state. These
µP supervisory circuits assert reset to prevent code-
execution errors during power-up, power-down, or
brownout conditions.
RESET and RESET are guaranteed to be asserted at a
valid logic level for VCC > +1V (see the Electrical Char-
acteristics table). Once RESET asserts, it remains
asserted for at least 100ms (tRP) after VCC rises above
its threshold value or after MR returns high (Figures 1
and 2).
Open-Drain
RESET
Output
The MAX6343 has an active-low, open-drain reset out-
put. This output sinks current when RESET is asserted.
Connect a pull-up resistor from RESET to any positive
supply voltage up to +5.5V (Figure 3). Select a resistor
value large enough to register a logic low (see the Elec-
trical Characteristics table), and small enough to regis-
ter a logic high while supplying all input current and
leakage paths connected to the RESET line. A 10kΩ
pull-up is sufficient in most applications.
Manual Reset
The MAX6342/MAX6343/MAX6344s’ manual-reset input
(MR) allows reset to be triggered by a pushbutton
switch. The switch is effectively debounced by the 1µs
min reset pulse width. MR is CMOS-logic compatible.
RESET
GENERATOR
VCC
6
(RESET)
5
RESET
4
PFO
1.25V
GND
100kΩ
VTH
( ) ARE FOR MAX6344 ONLY.
1
MR
2
VCC
3
PFI
MAX6342
MAX6343
MAX6344
RESET
GENERATOR
6
RESET
5
RESET
4
PFO
1.25V
GND
VTH
1
2
VCC
3
PFI
MAX6345
Figure 1. MAX6342/MAX6343/MAX6344 Functional Diagram Figure 2. MAX6345 Functional Diagram
MAX6342–MAX6345
Power-Fail Comparator
The power-fail comparator is useful for various purpos-
es because the power-fail output (PFO) is independent
of the reset output. The inverting input is internally con-
nected to a +1.25V reference.
To build an early-warning circuit for power failure, con-
nect the PFI pin to a voltage divider (see the Typical
Oper-ating Circuit). Choose the voltage-divider ratio so
that the voltage at PFI falls below +1.25V just before the
+5V regulator drops out. Use PFO to interrupt the µP to
prepare for an orderly shutdown.
Applications Information
Negative-Going VCC Transients
The MAX6342–MAX6345 supervisors are immune to
short-duration, negative-going VCC transients (glitches)
that usually do not require the entire system to shut down.
Figure 4 shows typical transient duration vs. reset com-
parator overdrive, for which the MAX6342–MAX6345 do
not generate a reset pulse. The graph was generated
using a negative-going pulse applied to VCC, starting
0.5V above the actual reset threshold and ending below
it by the magnitude indicated (reset comparator over-
drive). The graph indicates the maximum pulse width a
negative-going VCC transient can have without causing
a reset pulse. As the magnitude of the transient increas-
es (goes further below the reset threshold), the maxi-
mum allowable pulse width decreases.
Typically, a VCC transient that goes 100mV below the
reset threshold and lasts 12µs or less will not cause a
reset pulse. A 1µF bypass capacitor mounted as close
as possible to the VCC pin provides additional transient
immunity.
Ensuring a Valid Reset Output
Down to VCC = 0
The MAX6342–MAX6345 are guaranteed to operate
properly down to VCC = +1V. In applications that require
valid reset levels down to VCC = 0, a pulldown resistor to
active-low outputs (MAX6342/MAX6345) and a pullup
resistor to active-high outputs (MAX6344/MAX6345)
ensure that the reset line is valid when the reset output is
no longer sinking or sourcing current (Figures 5 and 6).
6-Pin µP Reset Circuit with
Power-Fail Comparator
6_______________________________________________________________________________________
MAX6343
VCC
GND
RESET RESET
µP
+5.0V
+3.3V
10kΩVCC
160
100
120
140
0
1 100 1000
60
40
20
80
RESET COMPARATOR OVERDRIVE, VTH - VCC (mV)
MAXIMUM TRANSIENT DURATION (µs)
10
MAX634_L/M
MAX634_T/S/R/Z
Figure 4. Maximum Transient Duration Magnitude Rejection
Figure 3. Open-Drain
RESET
Output Allows Use with Multiple
Supplies
VCC
VCC
GND
100kΩ
RESET
MAX6342
MAX6345
VCC
VCC
GND
100kΩ
RESET
MAX6344
MAX6345
Figure 5. Ensuring
RESET
Valid to VCC = 0 on Active-Low
Push-Pull Outputs
Figure 6. Ensuring
RESET
Valid to VCC = 0 on Active-High
Push-Pull Outputs
Note that this method does not work with the open-drain
output of the MAX6343. 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 threshold. For most
applications, 100kΩis adequate.
Monitoring Two Supplies
Monitor another voltage by connecting a resistor-divider
to PFI as shown in Figure 7. The threshold voltage will
then be given by:
VTH(PFI) = 1.25[(R1 + R2) / R2]
where VTH(PFI) is the threshold at which the monitored
voltage will trip PFO.
A good rule of thumb for selecting the resistors is to
choose R2 between 250kΩand 500kΩand solve for R1.
Connect PFO to MR in applications that require reset to
assert when the second voltage falls below its threshold.
Monitoring a Negative Voltage
Connect the circuit as shown in Figure 8 to use the
power-fail comparator to monitor a negative supply rail.
PFO stays low when V- is good. When V- rises to cause
PFI to be above +1.25V, PFO goes high. By adding the
resistors and transistor as shown, a high PFO triggers
reset. As long as PFO remains high, the MAX6342/
MAX6343/MAX6344 will keep reset asserted. Note that
the accuracy of this circuit depends on the PFI thresh-
old tolerance, the VCC line voltage, and the resistors.
Also, ensure that the voltage at PFI remains above
GND.
Interfacing to µPs with
Bidirectional Reset Pins
MAX6342–MAX6345
6-Pin µP Reset Circuit with
Power-Fail Comparator
_______________________________________________________________________________________ 7
VCC
VCC
R1
R2
V+
GND
( ) ARE FOR MAX6344 ONLY.
TO µP
PFI MR
PFO
RESET
(RESET)
MAX6342
MAX6343
MAX6344
Figure 7. Monitoring Two Supplies
VCC
VCC
R1
R1 R2
R2
V- GND
( ) ARE FOR MAX6344 ONLY.
VCC - 1.25V = 1.25V - VTRIP
100kΩ
100kΩ
PFI
MR
PFO
RESET
(RESET)
MAX6342
MAX6343
MAX6344
VTRIP < 0
Figure 8. Monitoring a Negative Voltage
VCC
GND
BUFFERED RESET TO
OTHER SYSTEM
COMPONENTS
4.7kΩ
RESET
MAX6342
MAX6345
VCC
GND
µP
RESET
Figure 9. Interfacing to µPs with Bidirectional Reset I/O
SOT Top Marks
PART SOT TOP
MARK PART SOT TOP
MARK
MAX6342LUT-T AACP MAX6344LUT-T AADQ
MAX6342MUT-T AACQ MAX6344MUT-T AADR
MAX6342TUT-T AACR MAX6344TUT-T AADS
MAX6342SUT-T AACS MAX6344SUT-T AADT
MAX6342RUT-T AACT MAX6344RUT-T AADU
MAX6342ZUT-T AACU MAX6344ZUT-T AADV
MAX6343LUT-T AACV MAX6345LUT-T AADW
MAX6343MUT-T AACW MAX6345MUT-T AADX
MAX6343TUT-T AACX MAX6345TUT-T AADY
MAX6343SUT-T AACY MAX6345SUT-T AADZ
MAX6343RUT-T AACZ MAX6345RUT-T AAEA
MAX6343ZUT-T AADA MAX6345ZUT-T AAEB
MAX6342–MAX6345
6-Pin µP Reset Circuit with
Power-Fail Comparator
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.
8_____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
©2005 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products, Inc.
VCC
PFI
MR PFO
µP
RESET
UNREGULATED DC
PUSHBUTTON
SWITCH
INTERRUPT
MAX6342
LINEAR
REGULATOR
RESET
VCC
GND
PFI
16
5
VCC
TOP VIEW
2
34
RESET
RESET
PFO
MAX6345
SOT23-6
Typical Operating Circuit Pin Configurations (continued)
TRANSISTOR COUNT: 403
Chip Information
6LSOT.EPS
PACKAGE OUTLINE, SOT 6L BODY
21-0058
1
1
G
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.)
