Rainbow Electronics DS8102 - Manual (Page 6)

DS8102
Dual Delta-Sigma Modulator and Encoder
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Once the power supply is at an acceptable level
(V
DD > V RST ) and the RST line is driven high, the
DS8102 exits shutdown mode. However, a warmup
sequence must then be completed before analog-to-
digital conversion and Manchester encoding begins.
The length of this sequence depends on the
internal/external voltage reference mode (controlled by
the APDREF pin).
If the external voltage reference is selected (APDREF = 1),
the following actions are performed:
1) Upon exit from shutdown mode (V DD > V RST and
RST = 1), the 8MHz oscillator is started.
2) The DS8102 delays for 16 cycles of the 8MHz oscil-
lator. This allows the 8MHz oscillator to warm up.
3) The analog front-end (AFE) is enabled.
4) The DS8102 delays for 8192 cycles of the 8MHz
oscillator. This allows the AFE to warm up.
5) If CLKSEL = 1, the 8MHz oscillator is disabled at
this point and the DS8102 switches to the external
clock source provided at CLKIO.
6) Both modulator channels are enabled, and the
DS8102 begins performing conversions using the
external voltage reference.
If the internal voltage reference is selected (APDREF = 0),
the followings actions are performed:
1) Upon exit from shutdown mode (V DD > V RST and
RST = 1), the 8MHz oscillator is started.
2) The DS8102 delays for 16 cycles of the 8MHz oscil-
lator. This allows the 8MHz oscillator to warm up.
3) The AFE is enabled.
4) The DS8102 delays for 8192 cycles of the 8MHz
oscillator. This allows the AFE to warm up.
5) The internal voltage reference is enabled.
6) The DS8102 delays for an additional 57,344 cycles
of the 8MHz oscillator. This allows the internal refer-
ence to warm up.
7) If CLKSEL = 1, the 8MHz oscillator is disabled at
this point and the DS8102 switches to the external
clock source provided at CLKIO.
8) Both modulator channels are enabled, and the
DS8102 begins performing conversions using the
internal voltage reference.
Even if the external clock has been selected by setting
CLKSEL = 1, the internal 8MHz oscillator is still used to
control the warmup sequence. Once the warmup
sequence has completed, the internal 8MHz oscillator
is disabled if CLKSEL = 1.
Active Mode
In active mode, the AFE and delta-sigma modulators on
the DS8102 are enabled, and the DS8102 converts and
outputs samples over the Manchester-encoded output
(MNOUT) at a rate determined by either the internal
8MHz oscillator (if CLKSEL = 0) or the external clock
input at CLKIO (if CLKSEL = 1).
If RST is driven low or if V DD drops below the V RST
level, the DS8102 enters shutdown mode immediately
and must go through the warmup sequence again
(once V
DD > V RST and RST = 1) to return to active
mode.
Configuration Inputs
The input pins G0, G1, APDREF, and CLKSEL are con-
figuration inputs for the DS8102 that determine its oper-
ating mode, including:
• Clock selection—internal or external
• Voltage reference—internal or external
• Gain setting for analog input channel 0—1x, 4x, 16x,
or 32x
These pins must be set to a valid level for proper oper-
ation; they cannot be left disconnected. If any of the
configuration inputs are driven by a companion micro-
controller (as opposed to being statically connected to
V
DD or GND), the inputs can only be changed when the
DS8102 is in shutdown mode.
Channel 0 Gain Selection
Configuration input pins G0 and G1 are used to select
the gain setting for analog input channel 0. The avail-
able gain configurations are 1x, 4x, 16x, and 32x. The
effective input voltage range scales downward propor-
tionally with each increased gain selection. For exam-
ple, full-scale output at gain = 1x occurs when AN0+ is
2V higher than AN0-. However, with the gain setting at
4x, the output reaches full scale when AN0+ is only
500mV higher than AN0-.
Table 1 lists the gain configuration settings available for
channel 0. The levels at G0 and G1 should be set when
the DS8102 is in shutdown mode.
G1 PIN G0 PIN GAIN
0 0 1x
0 1 4x
1 0 16x
1 1 32x
Table 1. Modulator 0 Gain Settings