Information

VREF_SC field descriptions (continued)
Field Description
10 Tight-regulation buffer enabled
11 Reserved
35.3 Functional Description
The Voltage Reference is a bandgap buffer system. Unity gain amplifiers are used.
The VREF_OUT signal is available as an internal reference when it is enabled. A 100 nF
capacitor must be connected between VREF_OUT and VSSA.
The following table shows all possible function configurations of the Voltage Reference.
Table 35-5. Voltage Reference function configurations
SC[VREFEN] SC[MODE_LV] Configuration Functionality
0 X Voltage Reference disabled Off
1 00 Voltage Reference enabled,
only the VREF bandgap is on
Startup and standby
1 01 Reserved Reserved
1 10 Voltage Reference enabled,
VREF bandgap and tight-
regulation buffer on
VREF_OUT available for
internal and external use. 100
nF capacitor is required.
1 11 Reserved Reserved
35.3.1 Voltage Reference Disabled, SC[VREFEN] = 0
When SC[VREFEN] = 0, the Voltage Reference is disabled, all bandgap and buffers are
disabled. The Voltage Reference is in off mode.
35.3.2 Voltage Reference Enabled, SC[VREFEN] = 1
When SC[VREFEN] = 1, the Voltage Reference is enabled, and different modes can be
set by the SC[MODE_LV] bits.
Functional Description
K20 Sub-Family Reference Manual, Rev. 6, Nov 2011
822 Freescale Semiconductor, Inc.