X9530 Datasheet, PDF (8/30 Pages) Xicor Inc. – Temperature Compensated Laser Diode Controller

X9530
VOLTAGE REFERENCE
The voltage reference to the A/D and D/A converters
on the X9530, 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 2).
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”.
Figure 2. Voltage Reference Structure
VRM: bit 2 in Control register 0.
VRef Pin
On-chip
Voltage
Reference
A/D Converter and
D/A Converters reference
A/D CONVERTER
The X9530 contains a general purpose, on-chip, 6-bit
Analog to Digital (A/D) converter whose output is
available at the Status Register as bits AD[5:0]. By
default these output bits are used to select a row in the
Figure 3. A/D Converter Block Diagram
look-up tables associated with the X9530’s Current
Generators. When bit ADCfiltOff is “0” (default), bits
AD[5:0] are updated each time the ADC performs four
consecutive conversions with the same exact result.
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 3. The voltage reference input (see “VOLTAGE
REFERENCE” for details), sets the maximum
amplitude of the ramp generator output. The A/D
converter input signal (see “A/D Converter Input
Select” below 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 3Fh
(63₁₀).
The A/D converter input voltage range (VIN_ADC) is
from 0 V to V(VRef).
A/D Converter Input Select
The input signal to the A/D converter on the X9530,
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 4). 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 Input
From VRef
Ramp
Generator
Comparator
6
Control and
Encode Logic
Conversion Reset
A/D Converter
Output
(To LUTs
and Status
Register)
Clock
REV 3.7 8/26/04
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Characteristics subject to change without notice. 8 of 30