CP3BT10 Datasheet, PDF (54/210 Pages) National Semiconductor (TI) – Reprogrammable Connectivity Processor with Bluetooth and USB Interfaces

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 CP3BT10. 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.
IOVCC
2.25V
11.7.2 Manual and SDI External Reset
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 CP3BT10 device operating from an IOVCC at 3.3V.
IOVCC
Core VCC
RESET
Main
Clock
2.25V
Manual
Reset
LM3724
5-Pin Reset
Circuit
10k Ω
IOVCC
CP3BT1x
RESET
GND
Power Up
Power Down
DS515
SDI Reset
DS509
Figure 5. Power-On Reset Timing
11.7.1 Simple External Reset
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 CP3BT10 device operating from an IO-
VCC at 3.0V to 3.3V.
Figure 7. Manual and SDI External Reset
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 CP3BT10 designs. If an SDI interface is not im-
plemented, an LM3722 with active pullup may be used.
IOVCC
LM809
3-Pin Reset
Circuit
IOVCC
CP3BT1x
RESET
GND
DS508
Figure 6. Simple External Reset
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