ne56605-42 NXP Semiconductors, ne56605-42 Datasheet - Page 9

• Manufacturer Part Number: ne56605-42
• Description: System Reset With Built-in Watchdog Timer
• Manufacturer: NXP Semiconductors

reset function in a single SO8 surface mount package. This provides
Philips Semiconductors
TECHNICAL DESCRIPTION
General discussion
The NE56605-42 combines a watchdog timer and an undervoltage
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 NE56605-42 outputs a reset signal to the
microprocessor. If the microprocessor supply voltage sags to
4.2 volts or less, the NE56605-42 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
NE56605-42 has complementary RESET and RESET outputs for
system use. The undervoltage detection threshold incorporates
hysteresis to prevent generating erratic resets.
The watchdog timer requires a pulse input. Normally this signal
comes from the system microprocessor’s clock. For operation, an
2003 Oct 15
System reset with built-in watchdog timer
C
C
P
7
3
54 k
26 k
R
V
5
PULSE
GENERATOR
CC
R
R
S Q
R
1.2 A
R
Figure 17. Functional diagram.
8.2 k
R
1 C
1.2 A
T
WD
6
0.2 V
C
0.1 V
9
supporting curves for performance over the full temperature range of
external capacitor (C
Normally a 0.1 F capacitor is used for C
fixed internal resistance establish the required minimum frequency
of watchdog input signal for the device to not output a reset signal.
In the absence of a watchdog input pulse, the C
to the 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.
Grounding the watchdog control pin (WD
watchdog function. Removing the ground from Pin 6, allowing it to
float, enables the watchdog function. Enabling or disabling the
watchdog function has no effect on 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
–30 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 Q
R
GND
S Q
R
T
) must be connected from Pin 1 to ground.
R
C
T
. The C
, Pin 6) disables the
NE56605-42
RESET
47 k
2
R
T
R
T
capacitor charges
capacitor and a
RESET
Product data
8
12 A
SL01293