JN5139/001,515 NXP Semiconductors, JN5139/001,515 Datasheet - Page 20

• Manufacturer Part Number: JN5139/001,515
• Description: IC MCU 32BIT 56QFN
• Manufacturer: NXP Semiconductors

Specifications of JN5139/001,515

• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

If the application requires a power supply reset to be used, i.e. removing and then applying VDD, it is important that
the device decoupling capacitors are completely discharged (less than 0.4v) before the VDD is re-applied. Failure to
do so may inhibit device operation. If complete discharge is difficult to achieve then it is recommended to use of an
external reset device to hold the device in reset whilst the voltage has dropped below the device operating voltage
range.
VDD
JN5139
R3
18k
RESETN
C16
470nF
Figure 11: External Reset Generation
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
) on its positive edge, the internal reset process starts.
RST
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, driven low, during the power-on reset and software reset. No
devices should drive the RESETN pin high.
V
RESETN pin
RST
Reset
Internal Reset
Figure 12: External Reset
6.3 Software Reset
A system reset can be triggered at any time through software control, causing a full chip reset and invalidating the
RAM contents. 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.
In addition, 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; otherwise a system reset will occur. Due to this, careful consideration
should be taken of any capacitance on this line. For instance, the RC values recommended in section 6.1 may need
to be replaced with a suitable reset IC.
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JN-DS-JN5139 1v9
© NXP Laboratories UK 2010