ne56625-20 NXP Semiconductors, ne56625-20 Datasheet - Page 9

• Manufacturer Part Number: ne56625-20
• Description: Ne56625-20 System Reset With Watchdog Timer
• Manufacturer: NXP Semiconductors

voltage portable, handheld communication and industrial equipment.
Philips Semiconductors
TECHNICAL DESCRIPTION
The NE56625-20 combines a Watchdog timer, a Battery Check and
an Undervoltage Reset functions in a single SO8 surface mount
package. This provides a space-saving solution for maintaining
proper operation of typical 2.0 volt cordless telephone and other low
While the Watchdog monitors the microprocessor operation, the
Battery Check and Undervoltage Reset monitor the supply voltage
to the microprocessor. If the microprocessor clock signal ceases or
becomes erratic, the NE56625-20 outputs a reset signal to the
microprocessor. If the microprocessor supply voltage sags to
2.0 volts or less, the NE56625-20 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 RESET output, the
NE56625-20 has a Battery Check output for system use. If the
supply voltage sags below 2.2 volts or less, the Battery Check
output goes LOW and remains LOW until the supply voltage
recovers. Both the undervoltage detection threshold and battery
check detection threshold incorporate hysteresis to prevent
generating erratic resets.
2003 Oct 15
System reset with Watchdog timer
C
C
CLK
V
S
7
3
250 k
V
5
CC
230 k
V
CC
GENERATOR
PULSE
1.25 V (typ.)
R
CT
S Q
R
Figure 16. Functional diagram.
2 BC
6
1 C
9
R
CT
T
resistor establishes, in part, the rate of charge of the C
supporting curves for performance over the full temperature range of
The Watchdog timer requires a pulse input. Normally this signal
comes from the system microprocessor’s clock. For operation, pin 6
is not connected (open) or an external resistor (R
greater is connected from Pin 6 to V
(C
capacitor is 2.2 nF to 2.2 F. The external R
capacitor establish the required minimum frequency of Watchdog
input signal for the device to not output a reset signal. The R
the absence of a Watchdog input pulse, the C
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.
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
–25 C to +100 C. Some degradation in performance will be
experienced at the temperature extremes and the system designer
should take this into account.
0.2 V
0.1 V
T
) is placed from Pin 1 to ground. The recommended range for C
4
S
R
Q
GND
S
R
Q
CC
and an external capacitor
NE56625-20
CT
T
resistor and C
capacitor charges to
CT
) of 1 M or
T
1 A
(typ.)
Product data
capacitor. In
SL01594
RESET
CT
T
8
T