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MAX7705CSA
レP Power-Supply Monitor with Reset
_______________General DescriptionIn applications with microprocessors (µPs) that have a
RESETinput, the MAX7705 is functionally and socket
compatible with the TL7705, but requires no external
components.It provides power-supply glitch immunity
and a guaranteed power-up reset delay, while typically
consuming 1/27ththe power from a +5V supply.
The MAX7705 monitors the power supply in µP and digital
systems. The RESEToutput is valid for VCCdown to 1V.
The device offers excellent circuit reliability and low cost
by eliminating external components and adjustments.
A system reset is provided during power-up, power-
down, and brownout conditions. When VCCis below the
reset threshold, RESETis low and holds the µP in reset.
RESETwill go high 280ms after VCCrises above the
reset threshold. The MAX7705 is available in 8-pin DIP
and SO packages.
________________________ApplicationsMinimum Component Count, Low-Cost
Processor Systems
____________________________FeaturesNo External ComponentsLow CostPrecise Reset Threshold280ms Power-On Reset Delay8-Pin DIP and SO Packages
______________Ordering Information* Contact factory for dice specifications.
MAX7705
µP Power-Supply Monitor
with Reset
________________________________________________________________Maxim Integrated Products1
__________________Pin Configuration
__________Typical Operating Circuit
Call toll free 1-800-998-8800 for free samples or literature.19-0151; Rev 0; 6/93
MAX7705
µP Power-Supply Monitor
with Reset_______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGSTerminal Voltage (with respect to GND)
VCC......................................................................-0.3V to 6.0V
RESET....................................................-0.3V to (VCC+ 0.3V)
Input Current, VCC..............................................................20mA
Output Current, RESET......................................................20mA
Rate-of-Rise, VCC............................................................100V/µs
Continuous Power Disipation (TA= +70°C)
Plastic DIP (derate 9.09mW/°C above +70°C)............727mW
SO (derate 5.88mW/°C above +70°C).........................471mW
Operating Temperature Ranges:
MAX7705C_ _.....................................................0°C to +70°C
MAX7705E_ _..................................................-40°C to +85°C
Storage Temperature Range.............................-65°C to +160°C
Lead Temperature (soldering, 10sec).............................+300°C
ELECTRICAL CHARACTERISTICS(VCC= full range, TA= TMINto TMAX, unless otherwise noted.)
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.
MAX7705
µP Power-Supply Monitor
with Reset
_______________________________________________________________________________________3POWER-DOWN RESET DELAY
vs. TEMPERATURE
TEMPERATURE (°C)
POWER-DOWN RESET DELAY (
POWER-UP RESET DELAY
vs. TEMPERATURE
TEMPERATURE (°C)
POWER-UP RESET DELAY (ms)
SUPPLY CURRENT
vs. TEMPERATURE
TEMPERATURE (°C)
SUPPLY CURRENT (
RESET THRESHOLD
vs. TEMPERATURE
TEMPERATURE (°C)
RESET THRESHOLD (V)
__________________________________________Typical Operating Characteristics
(TA = +25°C, unless otherwise noted.)
______________________________________________________________Pin Description
MAX7705
µP Power-Supply Monitor
with Reset_______________________________________________________________________________________
__________Applications Information
Replacing the TL7705 with a MAX7705
in an Existing DesignThe MAX7705 has only three active pins: VCC, GND,
and RESET. When using a TL7705 with a µP that has
a RESETinput, simply plug the MAX7705 into the
same socket and omit the RESETpull-up resistor, reset
timing capacitor, and reference bypass capacitor (see
the Typical Operating Circuit).
The MAX7705 monitors the VCCvoltage and asserts
reset whenever VCCfalls below the reset threshold.
The reset power-up delay is created by an internal
fixed oscillator. This delay is 100% tested and guaran-
teed over the full temperature range. The RESETout-
put both sources and sinks current (see RESETOutput
Voltage in the Electrical Characteristics).
Negative-Going VCCTransientsThe MAX7705 asserts RESETduring power-up,
power-down, and brownout conditions. However, it is
relatively immune to short-duration negative-going VCC
transients (glitches).
Figure 1 shows typical transient duration vs. reset com-
parator overdrive for which the MAX7705 does notgen-
erate a reset pulse. The graph was generated using a
fast-edge, negative-going pulse applied to VCC, starting
1.5V above the actual reset threshold and ending below
the reset threshold by the magnitude indicated (reset
comparator overdrive). It indicates the typical maxi-
mum pulse width a negative-going VCCtransient may
have without causing a reset pulse to be issued. As
the magnitude of the transient increases (goes farther
below the reset threshold), the maximum allowable
pulse width decreases. Typically, a VCCtransient that
goes 100mV below the reset threshold and lasts 40µs
or less will not cause a reset pulse to be issued.
A 0.1µF bypass capacitor mounted as close as possible
to pin 2 (VCC) provides additional transient immunity.
Ensuring a Valid RESET
Output
Down to VCC= 0VWhen VCCfalls below 1V, the MAX7705 RESEToutput
no longer sinks current; it becomes high impedance.
Therefore, high-impedance CMOS logic inputs con-
nected to the RESEToutput can drift to indeterminate
voltages. In most applications this presents no prob-
lem, as µP and other circuitry is generally inoperative
with VCCbelow 1V. In applications where the RESET
output must be valid down to 0V, adding a pull-down
resistor to the RESETpin (as shown in Figure 2) will
cause any stray leakage currents to flow to ground,
holding RESETlow. The resistance value of R1 is not
critical. It should be about 100kΩ, which is large
enough not to load RESETand small enough to pull
RESETto ground.
Figure 2.RESETValid to VCC= Ground Circuit
___________________Chip TopographyTRANSISTOR COUNT = 380;
SUBSTRATE CONNECTED TO VCC.
MAX7705
µP Power-Supply Monitor
with Reset
_______________________________________________________________________________________5Figure 3.Interfacing to µPs with Bidirectional Reset I/O
Interfacing to µPs with
Bidirectional Reset InputsµPs with bidirectional reset pins, such as Motorola’s
68HC11 series, can contend with the MAX7705 reset
output. If, for example, the MAX7705 RESEToutput is
asserted high and the µP wants to pull it low, an inde-
terminate logic level may result. To correct this, con-
nect a 4.7kΩresistor between the MAX7705 RESET
output and the µP reset I/O, as in Figure 3. Buffer the
RESETsignal to other system components.
MAX7705
µP Power-Supply Monitor
with Reset_______________________________________________________________________________________
_______________________________________________________Package Information
