DS1873T+ Maxim Integrated Products, DS1873T+ Datasheet - Page 20

• Manufacturer Part Number: DS1873T+
• Description: IC CTLR SFP+ ANLG LDD 28-TQFN
• Manufacturer: Maxim Integrated Products
• Type: Laser Diode Controllerr

Specifications of DS1873T+

• Number Of Channels: 1
• Voltage - Supply: 2.85 V ~ 3.9 V
• Current - Supply: 2.5mA
• Operating Temperature: -40°C ~ 95°C
• Package / Case: 28-WFQFN Exposed Pad
• Mounting Type: Surface Mount
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 90-1873T+000

standard digital PWM output given the same clock rate
and filter components. Before t
are high impedance.
The external RC filter components are chosen based
on ripple requirements, output load, delta-sigma fre-
quency, and desired response time. A recommended
filter is shown in Figure 10.
The DS1873’s delta-sigma outputs are 10 bits. For illus-
trative purposes, a 3-bit example is provided. Each
possible output of this 3-bit delta-sigma DAC is given in
Figure 11.
In LUT mode, MOD, DAC1, and DAC2 are each con-
trolled by an LUT with high-temperature resolution and
an OFFSET LUT with lower temperature resolution. The
SFP+ Controller with Analog LDD Interface
Figure 10. Recommended RC Filter for DAC1/DAC2
Figure 11. 3-Bit Delta-Sigma Example
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DS1873
DAC
0
1
2
3
4
5
6
7
3.24kΩ
0.01μF
3.24kΩ
INIT
, the DAC outputs
0.01μF
OUTPUT
MOD and DAC1 high-resolution LUTs each have 2°C
resolution. The DAC2 high-resolution LUT has 4°C reso-
lution. The OFFSET LUTs are located in the upper eight
registers (F8h–FFh) of the table containing each high-
resolution LUT. MOD DAC, DAC1 VALUE, and DAC2
VALUE are determined as follows:
Example calculation for MOD DAC:
Assumptions:
1) Temperature is 43°C.
2) Table 04h (MOD OFFSET LUT), Register FCh = 2Ah.
3) Table 04h (MOD LUT), Register A9h = 7Bh.
Because the temperature is 43°C, the MOD LUT index
is A9h and the MOD OFFSET LUT index is FCh.
When temperature controlled, the DACs are updated
after each temperature conversion.
The reference input, REFIN, is the supply voltage for all
four DACs. The voltage connected to REFIN and its
decoupling must be able to support the edge rate
requirements of the delta-sigma outputs.
DAC1 VALUE = DAC1 LUT + 4 x (DAC1 OFFSET LUT)
DAC2 VALUE = DAC1 LUT + 4 x (DAC1 OFFSET LUT)
MOD DAC = MOD LUT + 4 x (MOD OFFSET LUT)
MOD DAC = 7Bh + 4 x 2Ah = 123h = 291