SA56614-XX Datasheet, PDF (9/14 Pages) NXP Semiconductors – CMOS system reset

Philips Semiconductors
CMOS system reset
Product data
SA56614-XX
APPLICATION INFORMATION
V_DD
V_DD
CPU
SA56614-XX ^VOUT
RESET
V_SS
GND
SL01355
Figure 14. Conventional reset application
Small changes in supply current will occur when the SA56614
asserts or releases a reset. In some cases this can cause
oscillations of the device. This can present a problem, particularly
where high impedance V_DD sources are employed. Figure 15 shows
how this may occur.
R₁₁
V_SUPPLY
R₁₂
CURRENT CHANGES
A
V_DD
SA56614-XX
V_SS
OUTPUT
SL01356
Figure 15. High impedance supply operating problems
Significant voltage variations of V_DD may occur when the device is
operated from high impedance power sources. When the device
asserts or releases a reset, V_DD variations are produced as a result
of the voltage drop developed across R₁₁ due to the current
variations through the resistor R₁₁ (representing the supply
impedance). If the V_DD variations are large, such that they exceed
the Detection Hysteresis, the output of the device can oscillate from
a HIGH state to a LOW state. The user should avoid using high
impedance V_DD sources to prevent such situations.
2001 Jun 19
9