ne56604-42d NXP Semiconductors, ne56604-42d Datasheet - Page 9

• Manufacturer Part Number: ne56604-42d
• Description: System Reset With Built-in Watchdog Timer
• Manufacturer: NXP Semiconductors

Philips Semiconductors
TECHNICAL DESCRIPTION
General discussion
The NE56604-42 combines a Watchdog timer and an undervoltage
reset function in a single SO8 surface mount package. This provides
a space-saving solution for maintaining proper operation of typical
5.0 volt microprocessor-based logic systems. Either function, or
both, can force the microprocessor into a reset.
While the Watchdog monitors the microprocessor operation, the
undervoltage reset monitors the supply voltage to the
microprocessor. If the microprocessor clock signal ceases or
becomes erratic, the NE56604-42 outputs a reset signal to the
microprocessor. If the microprocessor supply voltage sags to
4.2 volts or less, the NE56604-42 outputs a reset signal for the
duration of the supply voltage deficiency. The undervoltage reset
signal allows the microprocessor to shut down in an orderly manner
to avoid system corruption. In addition to a single reset output, the
NE56604-42 has complementary RESET and RESET outputs for
system use. The undervoltage detection threshold incorporates
hysteresis to prevent generating erratic resets.
2003 Oct 15
System reset with built-in Watchdog timer
C
7
3
54 k
26 k
R
V
5
PULSE
GENERATOR
CC
R
R
58 k
R
CT
S Q
R
1.2 A
R
Figure 19. Functional diagram.
R
1 C
6
R
T
CT
0.2 V
0.1 V
9
The Watchdog timer requires a pulse input. Normally this signal
comes from the system microprocessor’s clock. For operation, an
external resistor (R
external capacitor (C
capacitor is used for C
establish the required minimum frequency of Watchdog input signal
for the device to not output a reset signal. The R
establishes, in part, the rate of charge of the C
absence of a Watchdog input pulse, the C
0.2 volt threshold of the internal comparator, causing a reset signal
to be output. If microprocessor clock signals are received within the
required interval, no Watchdog reset signal will be output. The
Watchdog function can be disabled by grounding Pin 6 without
affecting the undervoltage detection function.
Although the temperature coefficient of detection threshold is
specified over a temperature of –20 C to +70 C, the device will
support operation in excess of this temperature range. See the
supporting curves for performance over the full temperature range of
–40 C to +85 C. Some degradation in performance will be
experienced at the temperature extremes and the system designer
should take this into account.
4
S
R
Q
GND
S
R
Q
CT
T
) must be connected from Pin 6 to V
) from Pin 1 to ground. Normally a 0.1 F
T
. The external R
CT
R
T
resistor and C
NE56604-42
capacitor charges to the
RESET
47 k
2
T
R
capacitor. In the
R
CT
resistor
RESET
Product data
8
T
CC
capacitor
12 A
SL01310
and an