Principle of Operation
838
SLAU356I – March 2015 – Revised June 2019
Copyright © 2015–2019, Texas Instruments Incorporated
Reference Module (REF_A)
The REFMODEREQ request signal configures the bandgap and its bias circuitry to operate in a sampled
or static mode of operation. The REFMODEREQ signal represents a logical AND of individual requests
coming from the various analog modules. A REFMODEREQ occurs only if at least one analog module's
REFGENREQ or REFBGQ is also asserted, otherwise it is a don't care.
When REFMODEREQ = 1, the bandgap operates in sampled mode. When an analog module asserts its
corresponding REFMODEREQ signal, it is requesting that the bandgap operates in sampled mode.
Because REMODEREQ is a logical AND of all individual requests, any analog module requesting static
mode causes the bandgap to operate in static mode. The BGMODE bit can be read as an indicator of
static or sampled mode of operation.
21.2.2.1 REFBGACT, REFGENACT, REFGENBUSY
Any analog module that is using the variable reference line causes REFGENACT to be set inside the
REFCTL0 register. This bit is read only and indicates whether the REFGEN is active or off. Similarly, the
REFBGACT is active any time one or more analog modules are actively using the buffered bandgap
reference line. This bit is read only and indicates whether the REFBG is active or off.
The REFGENBUSY signal, when asserted, indicates that an analog module is using the reference and
cannot have any of it settings changed. For example, during an active ADC14 conversion, the reference
voltage level should not be changed. REFGENBUSY is asserted when there is an active ADC14
conversion. When it is asserted, REFGENBUSY write protects the REFCTL0 register. This prevents the
reference from being disabled or its level changed during any active conversion.
21.2.2.2 ADC14
For devices that contain an ADC14 module, there are two buffers. Refer to ADC14 block diagram in the
ADC14 chapter. The large buffer (BUF_EXT) can be used to drive the reference voltage, present on the
variable reference line, external to the device. This buffer has larger power consumption due to a
selectable burst mode as well as its need to drive larger DC loads that may be present outside the device.
The large buffer is enabled continuously when REFON = 1, REFOUT = 1, and ADC14REFBURST = 0.
When ADC14REFBURST = 1, the large buffer is enabled only during an ADC conversion, shutting down
automatically upon completion of a conversion to save power. In addition, when REFON = 1 and REFOUT
= 1, the second small buffer (BUF_INT) is automatically disabled. In this case, the output of the large
buffer is connected to the capacitor array through an internal analog switch. This ensures the same
reference is used throughout the system. If REFON = 1 and REFOUT = 0, the small buffer is used for
ADC conversion and the large buffer remains disabled. The small buffer can operate in burst mode as well
by setting ADC14REFBURST = 1.