JN5148 NXP Semiconductors, JN5148 Datasheet - Page 60

• Manufacturer Part Number: JN5148
• Description: The JN5148 is an ultra low power, high performance MCU combined with an IEEE802
• Manufacturer: NXP Semiconductors

interrupt can be modified to occur at the end of the chosen accumulation period, alternatively polling can still be used.
Software can then be used to apply the appropriate rounding and shifting to generate the average value, as well as
setting up the accumulation function.
For detailed electrical specifications, see section 22.3.8.
20.1.2 Supply Monitor
The internal supply monitor allows the voltage on the analogue supply pin VDD1 to be measured. This is achieved
with a potential divider that reduces the voltage by a factor of 0.666, allowing it to fall inside the input range of the
ADC when set with an input range twice the internal voltage reference. The resistor chain that performs the voltage
reduction is disabled until the measurement is made to avoid a continuous drain on the supply.
20.1.3 Temperature Sensor
The on chip temperature sensor can be used either to provide an absolute measure of the device temperature or to
detect changes in the ambient temperature. In common with most on chip temperature sensors, it is not trimmed and
so the absolute accuracy variation is large; the user may wish to calibrate the sensor prior to use. The sensor forces
a constant current through a forward biased diode to provide a voltage output proportional to the chip die temperature
which can then be measured using the ADC. The measured voltage has a linear relationship to temperature as
described in section 22.3.15.
Because this sensor is on chip, any measurements taken must account for the thermal time constants. For example,
if the device just came out of sleep mode the user application should wait until the temperature has stabilised before
taking a measurement.
20.2 Digital to Analogue Converter
The Digital to Analogue Converter (DAC) provides two output channels and is capable of producing voltages of 0 to
Vref or 0 to 2Vref where Vref is selected between the internal reference and the VREF pin, with a resolution of 12-bits
and a minimum conversion time of 10µsecs (2MHz clock).
20.2.1 Operation
The output range of each DAC can be set independently to swing between 0V to either the reference voltage or twice
the reference voltage. The reference voltage is selected from the internal reference or the VREF pin. For example,
an external reference of 0.8V supplied to VREF may be used to set DAC1 maximum output of 0.8V and DAC2
maximum output of 1.6V.
The DAC output amplifier is capable of driving a capacitive load up to that specified in section 22.3.9
Programmable clock periods allow a trade-off between conversion speed and resolution. The full 12-bit resolution is
achieved with the 250kHz clock rate. See section 22.3.9 electrical characteristics, for more details.
The conversion period of the DACs are given by the same formula as the ADC conversion time and so can vary
between 10 and 152uS. The DAC values may be updated at the same time as the ADC is active.
The clock divider ratio, interrupt enable and reference voltage select are all controlled through software, options
common to both the ADC and DAC. The DAC output range and initial value can be set and the subsequent updates
provided by updating only the DAC value. Polling is available to determine if a DAC channel is busy performing a
conversion. The DAC can be disabled which will power down the DAC cell.
Simultaneous conversions with DAC1 and DAC2 are possible. To use both DACs at the same time it is only
necessary to enable them and supply the digital values via the software. The DACs should not be used in single shot
mode, but continuous conversion mode only, in order to maintain a steady output voltage.
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JN-DS-JN5148-001 1v7
© NXP Laboratories UK 2011