X96012_08 Datasheet, PDF (13/23 Pages) Intersil Corporation – Universal Sensor Conditioner with Dual Look-up Table Memory and DACs

X96012
Voltage Reference
The voltage reference to the A/D and D/A converters on the
X96012, may be driven from the on-chip voltage reference,
or from an external source via the VREF pin. Bit VRM in
Control Register 0 selects between the two options. See
Figure 5.
The default value of VRM is “0”, which selects the internal
reference. When the internal reference is selected, it’s
output voltage is also an output at pin VREF with a nominal
value of 1.21 V. If an external voltage reference is preferred,
the VRM bit of the Control Register 0 must be set to “1”.
VRM: BIT 2 IN CONTROL REGISTER 0
VREF PIN
ON-CHIP
VOLTAGE
REFERENCE
A/D CONVERTER AND
D/A CONVERTERS REFERENCE
FIGURE 5. VOLTAGE REFERENCE STRUCTURE
A/D Converter
The X96012 contains a general purpose, on-chip, 8-bit
Analog to Digital (A/D) converter whose output is available at
the Status Register as bits AD[7:0]. By default these output
bits are used to select a row in the look-up tables associated
with the X96012’s Current Generators. When bit ADCfiltOff
is “0” (default), bits AD[7:0] are updated each time the ADC
performs four consecutive conversions with the same exact
result at the 6 MSBs. When bit ADCfiltOff is “1”, these bits
are updated after every ADC conversion.
A block diagram of the A/D converter is shown in Figure 6.
The voltage reference input (see “Voltage Reference” on
page 13), sets the maximum amplitude of the ramp
generator output. The A/D converter input signal (see “A/D
Converter Input Select” on page 13 for details) is compared
to the ramp generator output. The control and encode logic
produces a binary encoded output, with a minimum value of
00h (0₁₀), and a full scale output value of FFh (255₁₀).
The A/D converter input voltage range (VIN_ADC) is from 0V
to V(VREF).
A/D Converter Input Select
The input signal to the A/D converter on the X96012, may be
the output of the on-chip temperature sensor, or an external
source via the VSENSE pin. Bit ADCIN in Control register 0
selects between the two options. See Figure 7. It’s default
value is “0”, which selects the internal temperature sensor.
If an external source is intended as the input to the A/D
converter, the ADCIN bit of the Control register 0 must be set
to “1”.
A/D Converter Range
ADCIN: BIT 3 IN CONTROL REGISTER 0.
VSENSE
PIN
ON-CHIP
TEMPERATURE
SENSOR
TO A/D
CONVERTER
INPUT
VREF
FIGURE 7. A/D CONVERTER INPUT SELECT STRUCTURE
From Figure 6 we can see that the operating range of the
A/D converter input depends on the voltage reference. And
from Figure 7 we see that the internal temperature Sensor
output also varies with the voltage reference (VREF).
Table 4 summarizes the voltage range restrictions on the
VSENSE and VREF pins in different configurations.
TABLE 4. VSENSE AND VREF RANGES
VREF A/D CONVERTER INPUT
RANGES
Internal
Internal
External
Internal Temp Sensor
VSense Pin
VSense Pin
Not Applicable
0 ≤ V(VSense) ≤
V(VREF)
0 ≤ V(VREF) ≤ 1.3 V
0 ≤ V(VSense) ≤V(VREF)
External Internal Temp. Sensor Not a Valid Case
All voltages referred to V_SS
A/D CONVERTER INPUT
FROM VREF
RAMP
GENERATOR
COMPARATOR
8
CONTROL AND
ENCODE LOGIC
CONVERSION RESET
A/D CONVERTER
OUTPUT
(TO LUTS
AND STATUS
REGISTER)
CLOCK
13
FN8216.3
February 20, 2008