Page 1
General Description
The MAX7391 replaces ceramic resonators, crystals,
and supervisory functions for microcontrollers in 3.3V
and 5V applications.
The MAX7391 provides a clock source, reset, and
power-fail functions. The programmable power-fail function provides early warning of power failure and is configurable to detect either an external voltage or the V
CC
supply to the device.
The clock output can be switched between normal and
half-speed operation. This functionality allows the microcontroller to operate at reduced power and may be
used to extend the time available to perform housekeeping tasks, such as writing data to flash during a
power failure. Connecting the power-fail output to the
SPEED input reduces clock speed automatically during
power-fail events.
The MAX7391 clock output is factory programmed to a
frequency in the 1MHz to 16MHz range. Four standard
frequencies are available. Other frequencies are available upon request. The maximum operating supply current is 5.5mA (typ) with a clock frequency of 12MHz.
Unlike typical crystal and ceramic resonator oscillator
circuits, the MAX7391 is resistant to EMI and vibration,
and operates reliably at high temperatures. The highoutput drive current and absence of high-impedance
nodes make the oscillator invulnerable to dirty or humid
operating conditions.
The MAX7391 is available in an 8-pin µMAX
®
package.
The MAX7391 standard operating temperature range is
from -40°C to +125°C.
Applications
White Goods
Automotive
Appliances and Controls
Handheld Products
Portable Equipment
Microcontroller Systems
Features
♦ Robust Microcontroller Clock and Supervisory
Functions in a Single Package
♦ Integrated Reset and Power-Fail Functions
♦ Speed Select
♦ +2.7V to +5.5V Operation
♦ Factory-Trimmed Oscillator
♦ Reset Valid Down to 1.1V Supply Voltage
♦ ±10mA Clock-Output Drive Current
♦ ±4% Total Accuracy for -40°C to +125°C
♦ ±2.75% Total Accurac for 0°C to +85°C
♦ 5.5mA Operating Current (12MHz Version)
♦ -40°C to +125°C Temperature Range
♦ Surface-Mount Package
♦ 1MHz to 16MHz Factory Preset Frequency Range
MAX7391
Speed-Switching Clock Generator
with Power Fail
________________________________________________________________ Maxim Integrated Products 1
19-3981; Rev 0; 1/06
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.
SPEED
PFOGND
1
2
87CLOCK
RST/RSTV
CC
N.C.
PFI
TOP VIEW
µMAX
3
4
6
5
MAX7391
Pin Configuration
Ordering Information
Note: “s” is a placeholder for the reset output type. Insert the
symbol found in Table 2 in the place of “s.” “r” is a placeholder
for the power-on reset (POR) voltage. Insert the symbol found in
Table 1 in the place of “r.” “ff” is a placeholder for the nominal
output frequency. Insert the symbol found in Table 3 in the
place of “ff.” For example, MAX7391CMTP describes a device
with 4.38V reset level, open-collector
RST
output, and a clock
output frequency of 8MHz.
Typical Application Circuit, Functional Diagram, and Selector
Guide appear at end of data sheet.
µMAX is a registered trademark of Maxim Integrated Products, Inc.
PART TEMP RANGE PIN-PACKAGE
MAX7391srff -40°C to +125°C 8 µMAX U8-1
PKG
CODE
Page 2
MAX7391
Speed-Switching Clock Generator
with Power Fail
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
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.
VCCto GND...........................................................-0.3V to +6.0V
All Other Pins to GND ................................-0.3V to (V
CC
+ 0.3V)
CLOCK, RST/RST, PFO Output Current ..........................±50mA
Continuous Power Dissipation
8-Pin µMAX (derate 4.5mW/°C over T
A
= +70°C)........362mW
Operating Temperature Range .........................-40°C to +125°C
Junction Temperature......................................................+150°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
ELECTRICAL CHARACTERISTICS
(Typical Application Circuit, VCC= +2.7V to +5.5V, TA= -40°C to +125°C, 1MHz to 16MHz output frequency range, typical values at
V
CC
= +5.0V, TA= +25°C, unless otherwise noted.) (Note 1)
POWER REQUIREMENTS
Operating Supply Voltage V
Valid RST/RST Supply Voltage V
Operating Supply Current I
LOGIC INPUT: SPEED
Input Leakage Current I
Logic-Input High Voltage V
Logic-Input Low Voltage V
PUSH-PULL LOGIC OUTPUTS: RST/RST
Output High V
Output Low V
OPEN-DRAIN LOGIC OUTPUTS: RST, PFO
Output Low V
OUTPUT: CLOCK
CLOCK Output High Voltage V
CLOCK Output Low Voltage V
CLOCK Accuracy f
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
CC
CCR
LEAK
OLOISINK
OHCISOURCE
OLCISINK
CLOCK
Minimum supply voltage for valid RST/RST
output, T
f
= 12MHz 5.5
CC
OHISOURCE
OL
CLOCK
f
= 8MHz 4.5
CLOCK
Input is high 0.5 µA
IH
IL
I
= 3mA 0.05 0.4 V
SINK
= 3mA 0.05 0.4 V
= 5mA 0.3 V
Table 3, VCC = +5.0V -4 +4 %
2.7 5.5 V
= 0°C to +85°C
A
0.7 x V
CC
= 1mA VCC - 1.5 V
= 5mA VCC - 0.3 V
1.1 V
0.3 x V
CC
mA
V
V
Page 3
MAX7391
Speed-Switching Clock Generator
with Power Fail
_______________________________________________________________________________________ 3
ELECTRICAL CHARACTERISTICS (continued)
(Typical Application Circuit, VCC= +2.7V to +5.5V, TA= -40°C to +125°C, 1MHz to 16MHz output frequency range, typical values at
V
CC
= +5.0V, TA= +25°C, unless otherwise noted.) (Note 1)
Note 1: All parameters are tested at TA= +25°C. Specifications over temperature are guaranteed by design.
Note 2: Guaranteed by design. Not production tested.
Clock Frequency Temperature
Coefficient
Clock Frequency Supply Voltage
Coefficient
CLOCK Duty Cycle (Note 2) 45 50 55 %
CLOCK Output Jitter
Output Rise Time t
Output Fall Time t
INTERNAL POWER-ON RESET
Reset Voltage
Reset Timeout Period t
POWER FAIL
Power-Fail Select Threshold V
VCC Monitoring Threshold
(Internal Threshold)
Internal Threshold Hysteresis V
PFI Monitoring Threshold
(External Threshold)
External Threshold Hysteresis V
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
V
= +5.0V (Note 2) 140 400 ppm/°C
CC
= +25°C (Note 2) 0.67 1 %/V
T
A
Observation for 20s using a 500MHz
oscilloscope
C
R
(Note 2)
C
F
(Note 2)
V
TH+
V
RST
V
IHYSTVCC
V
ETH
EHYST
VCC rising, Table 1
VCC falling
TH-
Figure 1 86 135 250 µs
PFI input
SEL
VCC rising 4.06 4.38 4.60 V
ITH
PFI rising 0.9 1.1 1.4 V
PFI falling 1.0 3.5 8.0 %V
310
= 10pF, 10% to 90% of full scale
LOAD
= 10pF, 90% to 10% of full scale
LOAD
V
TA = +25°C
T
= -40°C to
A
+125°C
falling 1.0 2 4.0 %V
TH
- 1.5%
V
TH
- 2.5%
0.65 x
V
CC
2.5 7.0 ns
2.5 7.5 ns
V
TH
+ 1.5%
V
TH
+ 2.5%
0.98 x
V
TH+
0.85 x
V
CC
ps
RMS
V
V
ITH
ETH
Page 4
MAX7391
Speed-Switching Clock Generator
with Power Fail
4 _______________________________________________________________________________________
Typical Operating Characteristics
(Typical Application Circuit, VCC= +5V, f
CLOCK
= 16MHz, TA= +25°C, unless otherwise noted.)
FREQUENCY vs. SUPPLY VOLTAGE
MAX7391 toc01
VCC (V)
NORMALIZED FREQUENCY
4.854.203.55
0.990
1.000
1.010
1.020
0.980
2.90 5.50
NORMALIZED TO VCC = 5V
V
TH+
= 2.9V
FREQUENCY vs. TEMPERATURE
MAX7391 toc02
TEMPERATURE (°C)
NORMALIZED FREQUENCY
1109580655035205-10-25
0.990
1.000
1.010
1.020
1.030
1.040
0.980
-40 125
NORMALIZED TO TA = +25°C
DUTY CYCLE vs. SUPPLY VOLTAGE
MAX7391 toc03
VCC (V)
DUTY CYCLE (%)
4.854.203.55
49
50
51
52
48
2.90 5.50
V
TH+
= 2.9V
DUTY CYCLE vs. TEMPERATURE
MAX7391 toc04
DUTY CYCLE (%)
49
50
51
52
48
TEMPERATURE (°C)
1109580655035205-10-25-40 125
CLOCK OUTPUT WAVEFORM
WITH C
L
= 10pF
MAX7391 toc05
40ns/div
CLOCK
1V/div
VCC = 3.3V
CLOCK OUTPUT WAVEFORM
WITH C
L
= 50pF
MAX7391 toc06
40ns/div
CLOCK
1V/div
VCC = 3.3V
CLOCK OUTPUT WAVEFORM
WITH C
L
= 100pF
MAX7391 toc07
40ns/div
CLOCK
1V/div
SUPPLY CURRENT vs. TEMPERATURE
MAX7391 toc08
I
CC
(mA)
2
3
4
5
1
TEMPERATURE (°C)
1109580655035205-10-25-40 125
VCC = 5V
VCC = 3.3V
SUPPLY CURRENT vs. SUPPLY VOLTAGE
MAX7391 toc09
VCC (V)
I
CC
(mA)
4.854.203.55
2
3
4
5
1
2.90 5.50
V
TH+
= 2.9V
Page 5
MAX7391
Speed-Switching Clock Generator
with Power Fail
_______________________________________________________________________________________ 5
Typical Operating Characteristics (continued)
(Typical Application Circuit, VCC= +5V, f
CLOCK
= 16MHz, TA= +25°C, unless otherwise noted.)
CLOCK SETTLING TIME FROM START
1µs/div
MAX7391 toc10
CLOCK RESPONSE TO SPEED SELECT INPUT
V
CC
2V/div
CLOCK
2V/div
POWER-ON RESET BEHAVIOR
20µs/div
MAX7391 toc13
SPEED
2V/div
(V)
V
2.90
2.88
2.86
TH+
2.84
MAXIMUM VCC TRANSIENT DURATION
MAX7391 toc11
V
CC
5V/div
CLOCK
5V/div
RST
5V/div
PFO
5V/div
vs. RESET THRESHOLD OVERDRIVE
1000
RESET OCCURS ABOVE THIS CURVE
100
10
TRANSIENT DURATION (µs)
VCC FALLING FROM V
1
100 1000
RESET THRESHOLD OVERDRIVE (mV)
RISING THRESHOLD vs. TEMPERATURE
MAX7391 toc14
TH+
MAX7391 toc12
+ 100mV
900800700600500400300200
CLOCK
2V/div
200ns/div
2.82
2.80
-40 125
TEMPERATURE (°C)
1109580655035205-10-25
Page 6
Detailed Description
The MAX7391 replaces ceramic resonators, crystals,
and supervisory functions for microcontrollers in 3.3V
and 5V applications.
The MAX7391 provides a clock source, reset, and
power-fail functions. The power-fail output provides
early warning of power failure. The power-fail threshold
is configurable to detect either an external voltage or
the VCCsupply voltage to the device.
The clock output can be switched between normal and
half-speed operation. This functionality allows the
microcontroller to operate at reduced power and may
be used to extend the time available to perform housekeeping tasks, such as writing data to flash, during a
power failure. Connecting the power-fail output (PFO)
to the SPEED input reduces clock speed automatically
during power-fail events.
The integrated reset provides the power-supply monitoring functions necessary to ensure correct microcontroller
operation. The reset circuit has built-in power-supply
transient immunity and provides both power-on reset
and power-fail or brownout reset functionality. Two standard factory-trimmed reset levels are available.
A power-fail function is provided for power-supply voltage monitoring and can provide advance notice of an
impending power failure. The power-fail input monitors
external power-supply voltages through an external
resistive divider. Connect PFI to VCCto monitor VCC.
Clock Output (CLOCK)
The push-pull clock output (CLOCK) drives a groundconnected 1kΩ load or a positive supply connected
500Ω load to within 300mV of either supply rail. CLOCK
remains stable over the full operating voltage range and
does not generate short output cycles during either
power-on or power-off. A typical startup characteristic is
shown in the Typical Operating Characteristics section.
The clock output frequency is reduced by a factor of
two by taking SPEED low. This functionality allows the
microcontroller to operate at reduced power and may
be used to extend the time available to perform housekeeping tasks, such as writing data to flash during
power failure.
Reset
The reset function drives the microcontroller reset input
to prevent operation in the cases of the initial power-on
setting, low power-supply voltages, and the failed
watchdog operations. Three reset output versions are
available: push-pull RST, push-pull RST, and open-drain
RST. The reset timeout period (t
RST
) is nominally 135s.
Power-On Reset (POR)
The internal power-on reset (POR) circuit detects the
power-supply voltage (VCC) level at startup. The POR
circuit starts the oscillator when VCCexceeds the reset
rising threshold level (V
TH+
). The reset output remains
asserted from the time VCCcrosses the V
TH+
and con-
tinues to be asserted for the reset timeout period (t
RST
).
Upon completion of the reset timeout, the reset output
is released. See Figure 1.
MAX7391
Speed-Switching Clock Generator
with Power Fail
6 _______________________________________________________________________________________
Pin Description
PIN NAME FUNCTION
1 PFI
2V
3 N.C. No Connection
4 GND Ground
5 PFO
6 SPEED
7 RST/RST
8 CLOCK Clock Output
Power-Fail Input. PFI monitors the condition of either an external supplied voltage or V
section for more details.
Power Input. Connect VCC to the power supply. Bypass VCC to GND with a 0.1µF capacitor. Install the
CC
bypass capacitor as close to the device as possible.
Power-Fail Output. Open-drain output asserts when the voltage being monitored drops below the power-fail
threshold voltage.
Clock-Speed Select Input. Connect SPEED high for the factory-trimmed clock output frequency. Connect
SPEED low to reduce the clock output frequency by half.
Reset Output. Reset output is available in one of three configurations: push-pull RST, push-pull RST,
or open-drain RST. The reset output occurs if any combination of the following conditions occurs: reset
outp ut i s asser ted d ur i ng p ow er - up , and w henever V
r eset outp ut asser ts w hen W D I d oes not r ecei ve a r i si ng or fal l i ng ed g e w i thi n the w atchd og ti m eout p er i od .
i s b el ow the r eset thr eshol d l evel ; for d evi ces w i th W D I,
C C
. See the Power Fail
CC
Page 7
MAX7391
Speed-Switching Clock Generator
with Power Fail
_______________________________________________________________________________________ 7
Low-Voltage Lockout
The reset output asserts whenever V
CC
drops below the
reset falling threshold, V
TH-
. The difference between the
reset rising and falling threshold values is V
TH+
- (V
TH-
).
The nominal hysteresis value is 2% of the reset rising
threshold value. The reset detection circuitry provides
filtering to prevent triggering on negative voltage spikes.
See the Typical Operating Characteristics for a plot of
maximum transient duration without causing a reset
pulse vs. reset comparator overdrive.
Figure 1 shows the reset output (RST/RST) behavior
during power-up and brownout.
Power Fail
The power-fail function provides early warning of a power
failure. The power-fail comparator detects the condition
of either an external voltage or the VCCsupply voltage.
Internal (V
CC
) detection is configured by connecting
PFI to V
CC
. The internal V
CC
rising threshold (V
ITH
) is
set at 4.38V. The open-drain PFO asserts low if the V
CC
supply voltage drops below the VCCfalling threshold
value (V
IHYST
). The VCCfalling threshold is nominally
2% below the VCCrising threshold.
External power-fail detection is selected when the
applied voltage on PFI (V
PFI
) is less than 0.65 x V
CC
(V
SEL
minimum). When the voltage on PFI is more than
0.85 x VCC(V
SEL
maximum), the device switches to
internal monitoring. External power-fail detection is normally used with a resistive divider from the supply
being monitored. See the Typical Application Circuit.
For a 3.3V supply, the voltage on PFI needs to be set
externally and less than 0.65 x VCC(V
SEL
minimum). To set
the voltage on PFI externally, choose R1 and R2 so that:
See Figure 1 for PFO behavior during power-up and
brownout.
V
PFI
=
×+R PowerSupply
RR
2
21
Figure 1. RST/
RST
and
PFO
Behavior During Power-Up and Brownout
5
4
(V)
3
CC
V
2
V
ITH
V
TH+
V
- V
ITH
IHYST
V
TH-
1
CLK
t
RST
PFO
CLOCK STARTS ON INTERNAL
, VCC RISING).
POR (V
TH+
RST RELEASES AFTER THE
RESET TIMEOUT PERIOD.
PFO ASSERTS AS VCC DROPS
. CLOCK FREQUENCY
BELOW V
TH
REDUCTION SHOWN IS ACHIEVED
BY CONNECTING SPEED TO PFO.
RST ASSERTS ON RESET FALLING
VOLTAGE (V
CLOCK STOPS.
RST CONTINUES TO
ASSERT UNTIL V
, VCC FALLING).
TH-
.
CCR
RST
V
CCR
Page 8
MAX7391
Speed-Switching Clock Generator
with Power Fail
8 _______________________________________________________________________________________
Applications Information
Interfacing to a Microcontroller
Clock Input
The clock output is a push-pull, CMOS logic output,
which directly drives any microprocessor (µP) or microcontroller (µC) clock input. There are no impedancematching issues when using the MAX7391. Operate the
MAX7391 and µC (or other clock input device) from the
same supply voltage level. Refer to the microcontroller
data sheet for clock-input compatibility with external
clock signals. Table 3 lists clock output frequency.
The MAX7391 requires no biasing components or load
capacitance. When using the MAX7391 to retrofit a
crystal oscillator, remove all biasing components from
the oscillator input.
Power-Supply Considerations
The MAX7391 operates with power-supply voltages in
the 2.7V to 5.5V range. Good power-supply decoupling
is needed to maintain the power-supply rejection performance of the MAX7391. Bypass V
CC
to GND with a
0.1µF surface-mount ceramic capacitor. Mount the
bypass capacitor as close to the device as possible. If
possible, mount the MAX7391 close to the microcontroller’s decoupling capacitor so that additional decoupling is not required.
A larger-value bypass capacitor is recommended if the
MAX7391 is to operate with a large capacitive load.
Use a bypass capacitor value of at least 1000 times
that of the output load capacitance.
Output Jitter
The MAX7391’s jitter performance is given in the
Electrical Characteristics table as a peak-to-peak value
obtained by observing the output of the device for 20s
with a 500MHz oscilloscope. Jitter measurements are
approximately proportional to the period of the output
frequency of the device. Thus, a 4MHz part has approximately twice the jitter value of an 8MHz part.
The jitter performance of all clock sources degrades in
the presence of mechanical and electrical interference.
The MAX7391 is immune to vibration, shock, and EMI
influences, and thus provides a considerably more
robust clock source than crystal- or ceramic-resonatorbased oscillator circuits.
Table 1. POR Voltage
Table 2. Reset Output Type
Table 3. Clock Output Frequency
Note: Contact factory for other frequencies.
Note: Standard values are shown in bold. Contact factory for
other POR voltages.
Note: Standard values are shown in bold. Contact factory for
other output types.
Note: Other versions with different features are available. Refer to the MAX7387/MAX7388 and MAX7389/MAX7390 data sheets.
Selector Guide
PART
MAX7387 1 to 32 Yes Yes/yes Yes/yes — 10 µMAX
MAX7388 1 to 32 Yes Yes/no No/yes — 8 µMAX
MAX7389 1 to 32 Yes Yes/yes — — 8 µMAX
MAX7390 1 to 32 Yes Yes/no — Yes 8 µMAX
MAX7391 1 to 32 Yes — Yes/yes Yes 8 µMAX
FREQUENCY RANGE
(MHz)
RESET
FUNCTION
WATCHDOG INPUT
(WDI) / WATCHDOG
OUTPUT (WDO)
POWER-FAIL INPUT
(PFI)/POWER-FAIL
OUTPUT (PFO)
SPEED
PIN-
PACKAGE
POWER-ON RESET VOLTAGE (VTH) r
4.38 M
3.96 J
3.44 N
3.34 P
3.13 Q
2.89 S
2.82 V
2.5 X
OUTPUT TYPE s
Push-pull RST A
Push-pull RST B
Open collector RST C
CLOCK FREQUENCY (f
4RD
8TP
12 VB
16 WB
) (MHz) ff
CLOCK
Page 9
MAX7391
Speed-Switching Clock Generator
with Power Fail
_______________________________________________________________________________________ 9
Functional Diagram
Typical Application Circuit
Chip Information
PROCESS: BiCMOS
MAX7391
POWER-ON
RESET
PFI
INTERNAL (VCC DETECTION)
OSCILLATOR
GND
V_TH
PRESCALER
RST/RST
RESET TIMER
CLOCK
SPEED
PFO
N
POWER
SUPPLY
R1
R2
5V
DC-DC
V
CC
PFI
MAX7391
GND
RST/RST
PFO
SPEED
CLOCK
RST/RST
INT
µC
OSC1
Page 10
MAX7391
Speed-Switching Clock Generator
with Power Fail
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.
10 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2006 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products, Inc.
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
.)
8
0.6±0.1
0.6±0.1
1
TOP VIEW
A2
e
FRONT VIEW
Ø0.50±0.1
D
b
E H
A1
4X S
BOTTOM VIEW
A
c
L
SIDE VIEW
8
1
DIM
A
A1
A2
b
c
D
e
E
H
L
α
S
INCHES
MIN
-
0.002
0.030
0.010
0.005
0.116
0.0256 BSC
0.116
0.188
0.016
0°
0.0207 BSC
MAX
0.043
0.006
0.037
0.014
0.007
0.120
0.120
0.198
0.026
6°
MILLIMETERS
MIN
0.05 0.15
0.25 0.36
0.13 0.18
2.95 3.05
2.95 3.05
4.78
0.41
MAX
- 1.10
0.950.75
0.65 BSC
5.03
0.66
0.5250 BSC
8LUMAXD.EPS
6°0°
α
PROPRIETARY INFORMATION
TITLE:
PACKAGE OUTLINE, 8L uMAX/uSOP
REV.DOCUMENT CONTROL NO.APPROVAL
21-0036
1
J
1
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