4. Enable the internal regulator by setting VREF_SC[REGEN] to 1
37.4 Initialization/Application Information
The Voltage Reference requires some time for startup and stabilization. After
SC[VREFEN] = 1, SC[VREFST] can be monitored to determine if the stabilization and
startup is completed when the chop oscillator is not enabled. When the chop oscillator is
enabled, the settling time of the internal bandgap reference is defined by Tchop_osc_stup
(chop oscillator start up time). You must wait this time (Tchop_osc_stup) after the
internal bandgap has been enabled to ensure the VREF internal reference voltage has
stabilized.
When the Voltage Reference is already enabled and stabilized, changing SC[MODE_LV]
will not clear SC[VREFST] but there will be some startup time before the output voltage
at the VREF_OUT pin has settled. This is the buffer start up delay (Tstup) and the value
is specified in the appropriate device data sheet. Also, there will be some settling time
when a step change of the load current is applied to the VREF_OUT pin. When the 1.75V
VREF regulator is disabled, the VREF_OUT voltage will be more sensitive to supply
voltage variation. It is recommended to use this regulator to achieve optimum
VREF_OUT performance.
The TRM[CHOPEN], SC[REGEN] and SC[ICOMPEN] bits must be written to 1 to
achieve the performance stated in the device data sheet.
NOTE
See section "Internal voltage regulator" for details on the
required sequence to enable the internal regulator.
Chapter 37 Voltage Reference (VREFV1)
K22F Sub-Family Reference Manual, Rev. 4, 08/2016
NXP Semiconductors 865
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