User Manual
Jennic
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Jennic
20 JN-DS-JN5139 v1.5 © Jennic 2008
the operation of the internal power-on reset circuit. If complete discharge is difficult to achieve then it is recommended
that the external reset circuit, as shown in Figure 11, be used.
RESETN
C1
R1
JN5139
VDD
10k
100nF
Figure 11: External Reset Generation
The external resistor and capacitor provide a simple reset operation when connected to the RESETN pin.
6.2 External Reset
An external reset is generated by a low level on the RESETN pin. Reset pulses longer than the minimum pulse width
will generate a reset during active or sleep modes. Shorter pulses are not guaranteed to generate a reset. The
JN5139 is held in reset while the RESETN pin is low and when the applied signal reaches the Reset Threshold
Voltage (V
RST
) on its positive edge, the internal reset process starts.
Multiple devices may connect to the RESETN pin in an open-collector mode. The JN5139 has an internal pull-up
resistor although an external pull-up resistor is recommended when multiple devices connect to the RESETN pin.
The pin is an input for an external reset and an output during the power-on reset and software reset. No devices
should drive the RESETN pin high.
V
RST
Internal Reset
RESETN pin
Reset
Figure 12: External Reset
6.3 Software Reset
The RESETN line can be driven low by the JN5139 to provide a reset to other devices in the system (e.g. external
sensors) without resetting itself. When the RESETN line is not driven it will pull back high through either the internal
pull-up resistor or any external circuitry. It is essential to ensure that the RESETN line pulls back high within 100µsec
after the JN5139 stops driving the line (careful consideration should be taken for any capacitance on this line).
A system reset can be triggered at any time through software control. For example this can be executed within a
user’s application, upon detection of a system failure. When performing the reset, the RESETN pin is driven low for
1µsec; depending on the external components this may or may not be visible on the pin.