cp3ub17 National Semiconductor Corporation, cp3ub17 Datasheet - Page 54

• Manufacturer Part Number: cp3ub17
• Description: Reprogrammable Connectivity Processor With Usb Interface
• Manufacturer: National Semiconductor Corporation

www.national.com
The external reset circuits presented in the following sec-
tions provide varying levels of additional fault tolerance and
expandability and are presented as possible examples of
solutions to be used with the CP3UB17. It is important to
note, however, that any design for the reset circuit and pow-
er supply must meet the timing requirements shown in
Figure 5.
11.7.1
A simple external reset circuit with brown-out and glitch pro-
tection based on the LM809 3-Pin Microprocessor Reset
Circuit is shown in Figure 6. The LM809 produces a 240-ms
logic low reset pulse when the power supply rises above a
threshold voltage. Various reset thresholds are available for
the LM809, however the options for 2.93V and 3.08V are
most suitable for a CP3UB17 device operating from an IO-
VCC at 3.0V to 3.3V.
Core VCC
RESET
IOVCC
Clock
Main
Simple External Reset
Figure 5. Power-On Reset Timing
Figure 6. Simple External Reset
3-Pin Reset
Power Up
IOVCC
LM809
Circuit
IOVCC
RESET
GND
CP3xx17
Power Down
DS512
DS515
2.25V
2.25V
54
11.7.2
An external reset circuit based on the LM3724 5-Pin Micro-
processor Reset Circuit is shown in Figure 7. The LM3724
produces a 190-ms logic low reset pulse when the power
supply rises above a threshold voltage or a manual reset
button is pressed. Various reset thresholds are available for
the LM3724, however the option for 3.08V is most suitable
for a CP3UB17 device operating from an IOVCC at 3.3V.
The LM3724 provides a debounced input for a manual
pushbutton reset switch. It also has an open-drain output
which can be used for implementing a wire-OR connection
with a reset signal from a serial debug interface. This circuit
is typical of a design to be used in a development or evalu-
ation environment, however it is a good recommendation for
all general CP3UB17 designs. If an SDI interface is not im-
plemented, an LM3722 with active pullup may be used.
Manual
Reset
Figure 7. Manual and SDI External Reset
Manual and SDI External Reset
5-Pin Reset
LM3724
IOVCC
Circuit
SDI Reset
10k Ω
IOVCC
RESET
GND
CP3xx17
DS513