19-3981; Rev 0; 1/06
Speed-Switching Clock Generator
with Power Fail
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 func-
tion provides early warning of power failure and is con-
figurable 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 micro-
controller to operate at reduced power and may be
used to extend the time available to perform house-
keeping 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 avail-
able upon request. The maximum operating supply cur-
rent 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 high-
output 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.
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
Ordering Information
PART
MAX7391srff
TEMP RANGE
-40°C to +125°C
PIN-PACKAGE
8 µMAX
PKG
CODE
U8-1
Applications
White Goods
Automotive
Appliances and Controls
Handheld Products
Portable Equipment
Microcontroller Systems
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.
Pin Configuration
TOP VIEW
PFI 1
V
CC
2
8 CLOCK
7 RST/RST
Typical Application Circuit, Functional Diagram, and Selector
Guide appear at end of data sheet.
µMAX is a registered trademark of Maxim Integrated Products, Inc.
MAX7391
6 SPEED
5 PFO
N.C. 3
GND 4
µMAX
________________________________________________________________
Maxim Integrated Products
1
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-Switching Clock Generator
with Power Fail
MAX7391
ABSOLUTE MAXIMUM RATINGS
V
CC
to 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
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.
ELECTRICAL CHARACTERISTICS
(Typical
Application Circuit,
V
CC
= +2.7V to +5.5V, T
A
= -40°C to +125°C, 1MHz to 16MHz output frequency range, typical values at
V
CC
= +5.0V, T
A
= +25°C, unless otherwise noted.) (Note 1)
PARAMETER
POWER REQUIREMENTS
Operating Supply Voltage
Valid RST/RST Supply Voltage
Operating Supply Current
LOGIC INPUT: SPEED
Input Leakage Current
Logic-Input High Voltage
Logic-Input Low Voltage
PUSH-PULL LOGIC OUTPUTS: RST/RST
Output High
Output Low
Output Low
OUTPUT: CLOCK
CLOCK Output High Voltage
CLOCK Output Low Voltage
CLOCK Accuracy
V
OHC
V
OLC
f
CLOCK
I
SOURCE
= 5mA
I
SINK
= 5mA
Table 3, V
CC
= +5.0V
-4
V
CC
- 0.3
0.3
+4
V
V
%
V
OH
V
OL
V
OLO
I
SOURCE
= 1mA
I
SINK
= 3mA
I
SINK
= 3mA
V
CC
- 1.5
0.05
0.05
0.4
0.4
V
V
V
I
LEAK
V
IH
V
IL
Input is high
0.7 x V
CC
0.3 x V
CC
0.5
µA
V
V
V
CC
V
CCR
I
CC
Minimum supply voltage for valid RST/RST
output, T
A
= 0°C to +85°C
f
CLOCK
= 12MHz
f
CLOCK
= 8MHz
2.7
5.5
1.1
5.5
4.5
V
V
mA
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
OPEN-DRAIN LOGIC OUTPUTS:
RST, PFO
2
_______________________________________________________________________________________
Speed-Switching Clock Generator
with Power Fail
ELECTRICAL CHARACTERISTICS (continued)
(Typical
Application Circuit,
V
CC
= +2.7V to +5.5V, T
A
= -40°C to +125°C, 1MHz to 16MHz output frequency range, typical values at
V
CC
= +5.0V, T
A
= +25°C, unless otherwise noted.) (Note 1)
PARAMETER
Clock Frequency Temperature
Coefficient
Clock Frequency Supply Voltage
Coefficient
CLOCK Duty Cycle
CLOCK Output Jitter
Output Rise Time
Output Fall Time
INTERNAL POWER-ON RESET
T
A
= +25°C
V
TH+
Reset Voltage
V
TH-
Reset Timeout Period
POWER FAIL
Power-Fail Select Threshold
V
CC
Monitoring Threshold
(Internal Threshold)
Internal Threshold Hysteresis
PFI Monitoring Threshold
(External Threshold)
External Threshold Hysteresis
V
SEL
V
ITH
V
IHYST
V
ETH
V
EHYST
PFI input
V
CC
rising
V
CC
falling
PFI rising
PFI falling
0.65 x
V
CC
4.06
1.0
0.9
1.0
4.38
2
1.1
3.5
0.85 x
V
CC
4.60
4.0
1.4
8.0
V
V
%V
ITH
V
%V
ETH
t
RST
V
CC
falling
Figure 1
86
V
CC
rising, Table 1
T
A
= -40°C to
+125°C
V
TH
- 1.5%
V
TH
- 2.5%
0.98 x
V
TH+
135
250
µs
V
TH
+ 1.5%
V
TH
+ 2.5%
V
t
R
t
F
SYMBOL
CONDITIONS
V
CC
= +5.0V (Note 2)
T
A
= +25°C (Note 2)
(Note 2)
Observation for 20s using a 500MHz
oscilloscope
C
LOAD
= 10pF, 10% to 90% of full scale
(Note 2)
C
LOAD
= 10pF, 90% to 10% of full scale
(Note 2)
45
MIN
TYP
140
0.67
50
310
2.5
2.5
7.0
7.5
MAX
400
1
55
UNITS
ppm/°C
%/V
%
ps
RMS
ns
ns
MAX7391
Note 1:
All parameters are tested at T
A
= +25°C. Specifications over temperature are guaranteed by design.
Note 2:
Guaranteed by design. Not production tested.
_______________________________________________________________________________________
3
Speed-Switching Clock Generator
with Power Fail
MAX7391
Typical Operating Characteristics
(Typical
Application Circuit,
V
CC
= +5V, f
CLOCK
= 16MHz, T
A
= +25°C, unless otherwise noted.)
FREQUENCY vs. SUPPLY VOLTAGE
MAX7391 toc01
FREQUENCY vs. TEMPERATURE
MAX7391 toc02
DUTY CYCLE vs. SUPPLY VOLTAGE
MAX7391 toc03
1.020
1.040
1.030
NORMALIZED FREQUENCY
1.020
1.010
1.000
0.990
0.980
NORMALIZED TO T
A
= +25°C
52
NORMALIZED FREQUENCY
1.010
51
DUTY CYCLE (%)
1.000
50
0.990
NORMALIZED TO V
CC
= 5V
V
TH+
= 2.9V
0.980
2.90
3.55
4.20
V
CC
(V)
4.85
5.50
49
V
TH+
= 2.9V
48
2.90
3.55
4.20
V
CC
(V)
4.85
5.50
-40 -25 -10 5 20 35 50 65 80 95 110 125
TEMPERATURE (°C)
DUTY CYCLE vs. TEMPERATURE
MAX7391 toc04
CLOCK OUTPUT WAVEFORM
WITH C
L
= 10pF
MAX7391 toc05
CLOCK OUTPUT WAVEFORM
WITH C
L
= 50pF
MAX7391 toc06
52
V
CC
= 3.3V
V
CC
= 3.3V
51
DUTY CYCLE (%)
50
CLOCK
1V/div
CLOCK
1V/div
49
48
-40 -25 -10 5 20 35 50 65 80 95 110 125
TEMPERATURE (°C)
40ns/div
40ns/div
CLOCK OUTPUT WAVEFORM
WITH C
L
= 100pF
MAX7391 toc07
SUPPLY CURRENT vs. TEMPERATURE
MAX7391 toc08
SUPPLY CURRENT vs. SUPPLY VOLTAGE
MAX7391 toc09
5
5
4
I
CC
(mA)
CLOCK
1V/div
V
CC
= 5V
4
I
CC
(mA)
3
V
CC
= 3.3V
2
3
2
V
TH+
= 2.9V
1
40ns/div
-40 -25 -10 5 20 35 50 65 80 95 110 125
TEMPERATURE (°C)
1
2.90
3.55
4.20
V
CC
(V)
4.85
5.50
4
_______________________________________________________________________________________
Speed-Switching Clock Generator
with Power Fail
MAX7391
Typical Operating Characteristics (continued)
(Typical
Application Circuit,
V
CC
= +5V, f
CLOCK
= 16MHz, T
A
= +25°C, unless otherwise noted.)
CLOCK SETTLING TIME FROM START
MAX7391 toc10
POWER-ON RESET BEHAVIOR
MAX7391 toc11
MAXIMUM V
CC
TRANSIENT DURATION
vs. RESET THRESHOLD OVERDRIVE
MAX7391 toc12
1000
V
CC
5V/div
V
CC
2V/div
TRANSIENT DURATION (µs)
RESET OCCURS ABOVE THIS CURVE
100
CLOCK
2V/div
CLOCK
5V/div
RST
5V/div
PFO
5V/div
10
V
CC
FALLING FROM V
TH+
+ 100mV
1
100 200 300 400 500 600 700 800 900 1000
RESET THRESHOLD OVERDRIVE (mV)
1µs/div
20µs/div
CLOCK RESPONSE TO SPEED SELECT INPUT
MAX7391 toc13
RISING THRESHOLD vs. TEMPERATURE
MAX7391 toc14
2.90
SPEED
2V/div
V
TH+
(V)
2.88
2.86
2.84
CLOCK
2V/div
2.82
2.80
200ns/div
-40 -25 -10 5 20 35 50 65 80 95 110 125
TEMPERATURE (°C)
_______________________________________________________________________________________
5
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