dallas semiconductor DS1233 service manual

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DS1233

5V EconoReset

FEATURES

PIN ASSIGNMENT

§ Automatically restarts microprocessor after

power failure

§ Monitors pushbutton for external override

§ Internal circuitry debounces pushbutton

DALLAS
DS1233

Econo

Reset

switch

§ Maintains reset for 350ms after VCC returns to

an in-tolerance condition or pushbutton
released

§ Accurate 5%, 10%, or 15% microprocessor

5V power supply monitoring

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1

§ Reduces need for discrete components

§ Precision temperature-compensated voltage

reference and voltage sensor

§ Low-cost TO-92 package or surface-mount

SOT-223 package

§ Internal 5kW pull-up resistor

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BOTTOM VIEW

TO-92 PACKAGE

See Mech.

Drawings Section

on Website

4

2

TOP VIEW

SOT-223 PACKAGE

See Mech.

Drawings Section

on Website

§ Operating temperature of -40°C to +85°C

PIN DESCRIPTION

PIN 1 GROUND

PIN 2 RESET
PIN 3 V

CC

PIN 4 GROUND (SOT-223 ONLY)

DESCRIPTION

The DS1233 EconoReset monitors two vital conditions for a microprocessor: power supply and external
override. A precision temperature-compensated reference and comparator circuit are used to monitor the
status of the power supply (V
signal is generated which forces reset to the active state. When VCC returns to an in-tolerance condition,
the reset signal is kept in the active state for approximately 350ms to allow the power supply and
processor to stabilize. The second function of the DS1233 is pushbutton reset control. The DS1233
debounces a pushbutton closure and will generate a 350ms reset pulse upon release.

). When an out-of-tolerance condition is detected, an internal power-fail

CC

OPERATION — POWER MONITOR

The DS1233 provides the functions of detecting out-of-tolerance power supply conditions and warning a
processor-based system of impending power failure. When VCC is detected as out-of-tolerance, as

defined by the tolerance of the part selected, the
for approximately 350ms after the power supply has reached the selected tolerance. This allows the power

supply and microprocessor to stabilize before RST is released.

RST signal is asserted. On power-up, RST is kept active

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DS1233

OPERATION — PUSHBUTTON RESET

The DS1233 provides for a pushbutton switch to be connected to the RST output pin. When the DS1233

is not in a reset cycle, it continuously monitors the RST signal for a low going edge. If an edge is

detected, the DS1233 will debounce the switch by pulling the RST line low. After the internal timer has

expired, the DS1233 will continue to monitor the RST line. If the line is still low, the DS1233 will
continue to monitor the line looking for a rising edge. Upon detecting a release, the DS1233 will force the

RST line low and hold it low for 350ms.

NOTE:

For proper operation with an external pushbutton, a capacitor between 100pF and 0.01mF must be

connected between
minimum capacitance of 500pF should be used, along with a parallel external pull-up resistor of
1kW minimum.

RST and ground. In applications where additional reset current is required, a

BLOCK DIAGRAM Figure 1

APPLICATION EXAMPLE Figure 2

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