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G684 Schematic ( PDF Datasheet ) - GMT

Teilenummer G684
Beschreibung (G684 / G685) Microprocessor Reset IC
Hersteller GMT
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Gesamt 7 Seiten
G684 Datasheet, Funktion
www.DataSheet4U.com
Global Mixed-mode Technology Inc.
G684/G685
Microprocessor Reset IC
Features
„Precision Monitoring of +3V, +3.3V, and +5V
Power-Supply Voltages
„Fully Specified Over Temperature
„Available in Three Output Configurations
Push-Pull RESET Output (G684L)
Push-Pull RESET Output (G684H)
Open-Drain RESET Output (G685L)
„14µA Supply Current
„Guaranteed Reset Valid to VCC = 0.8V
„Power Supply Transient Immunity
„5 pin SOT23-5 Packages
„2% Threshold Accuracy
Applications
„Computers
„Controllers
„Intelligent Instruments
„Critical µP and µC Power Monitoring
„Portable / Battery-Powered Equipment
„Automotive
Pin Configuration
General Description
The G684/G685 are microprocessor (µP) supervisory
circuits used to monitor the power supplies in µP and
digital systems. They provide excellent circuit reliability
and low cost and adjustments when used with +5V,
+3.3V, +3.0V- powered circuits.
These circuits perform a single function: they assert a
reset signal whenever the VCC supply voltage declines
below a preset threshold, with hysteresis after VCC has
risen above the reset threshold. Reset thresholds
suitable for operation with a variety of supply voltages
are available.
The G685 has an open-drain output stage, while the
G684 have push-pull outputs. The G685L’s open-drain
RESET output requires a pull-up resistor that can be
connected to a voltage higher than VCC. The G684L
have an active-low RESET output, while the G684H
has an active-high RESET output. The reset com-
parator is designed to ignore fast transients on VCC,
and the outputs are guaranteed to be in the correct
logic state for VCC down to 0.8V.
Low supply current makes the G684/G685 ideal for
use in portable equipment. The G684/G685 are avail-
able in 5-pin SOT23-5 packages.
Ordering Information
ORDER NUMBER TEMP. RANGE PACKAGE
G684H(L)xxxT1U -40°C ~ +105°C
SOT23-5
G685LxxxT1U
-40°C ~ +105°C
SOT23-5
Note: T1 : SOT23-5
U : Tape & Reel
* xxx specifies the threshold voltage.
e.g. 263 denotes the 2.63V threshold voltage.
Typical Application Circuit
N.C. 1
5 VCC
GND 2 G684/G685
GND 3
SOT23-5
()is for G684H
4 RESET
(RESET)
VCC
VCC
G684/G685
RESET
(RESET)
GND
Rpull-up*
VCC
µP
RESET
INPUT
GND
*G685 ONLY
Ver: 1.2
Jun 03, 2004
TEL: 886-3-5788833
http://www.gmt.com.tw
1






G684 Datasheet, Funktion
Global Mixed-mode Technology Inc.
Interfacing to µPs with Bidirectional Reset Pins
Since the RESET output on the G685L is open drain,
this device interfaces easily with µPs that have bidirec-
tional reset pins, such as the Motorola 68HC11. Connect-
ing the µP supervisor’s RESET output directly to the
microcontroller’s (µC’s) RESET pin with a single pull-up
resistor allows either device to assert reset (Figure 3).
+3.3V
VCC
G685
RESET
G684/G685
+5.0V
RPULL-UP
VCC
5V SYSTEM
RESET
INPUT
VCC
VCC
G685
RESET
RPULL-UP
VCC
µP
RESET MOTOROLA
INPUT 68HCXX
GND
GND
Figure 4. G685L Open-Drain RESET Output Allows
Use with Multiple Supplies
GND
GND
Figure 3. Interfacing to µPs with Bidirectional Reset
I/O
G685L Open-Drain RESET Output Allows Use with
Multiple Supplies
Generally, the pull-up connected to the G685L will
connect to the supply voltage that is being monitored at
the IC’s VCC pin. However, some systems may use the
open-drain output to level-shift from the monitored sup-
ply to reset circuitry powered by some other supply
(Figure 4). Note that as the G685L’s VCC decreases
below 1V, so does the IC’s ability to sink current at
RESET . Also, with any pull-up, RESET will be pulled
high as VCC decays toward 0. The voltage where this
occurs depends on the pull-up resistor value and the
voltage to which it is connected.
Benefits of Highly Accurate Reset Threshold
Most µP supervisor ICs have reset threshold voltages
between 5% and 10% below the value of nominal sup-
ply voltages. This ensures a reset will not occur within
5% of the nominal supply, but will occur when the sup-
ply is 10% below nominal.
When using ICs rated at only the nominal supply ±5%,
this leaves a zone of uncertainty where the supply is
between 5% and 10% low, and where the reset may or
may not be asserted.
The G68_ _463/G68_ _308 use highly accurate circuitry to
ensure that reset is asserted close to the 5% limit, and
long before the supply has declined to 10% below nominal.
Ver: 1.2
Jun 03, 2004
TEL: 886-3-5788833
http://www.gmt.com.tw
6

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