DS1876 datasheet(16/69 Pages) MAXIM

16 / 69 page

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SFP Controller with Dual LDD Interface

For all device addresses sourced from EEPROM (Table

02h, Register 8Bh), the default device addresses are

A2h and B2h until VCC exceeds POA allowing the device

address to be recalled from the EEPROM.

Delta-Sigma Outputs

Four delta-sigma outputs are provided: MOD1, MOD2,

APC1, and APC2. With the addition of an external RC

filter, these outputs provide 10-bit resolution analog

outputs with the full-scale range set by the input REFIN.

Each output is either manually controlled or controlled

using a temperature-indexed LUT.

A delta-sigma DAC has a digital output using pulse-

density modulation. It provides much lower output ripple

than a standard digital PWM output given the same clock

rate and filter components. Before tINIT, the DAC outputs

are high impedance. The external RC filter components

are chosen based on ripple requirements, output load,

delta-sigma frequency, and desired response time.

Figure 6 shows a recommended filter.

For illustrative purposes, a 3-bit example is provided in

Figure 7.

In LUT mode the DACs are each controlled by an LUT

with high-temperature resolution and an OFFSET LUT

with lower temperature resolution. The high-resolution

LUTs each have 2NC resolutions. The OFFSET LUTs

are located in the upper eight registers (F8h

-FFh) of

the table containing each high-resolution LUT. The DAC

values are determined as follows:

DAC value = LUT + 4 x (OFFSET LUT)

An example calculation for MOD1 DAC is as follows:

Assumptions:

1) Temperature is +43NC

2) Table 04h (MOD1 OFFSET LUT), Register FCh = 2Ah

3) Table 04h (MOD1 LUT), Register AAh = 7Bh

Because the temperature is +43NC, the MOD1 LUT index

is AAh and the MOD1 OFFSET LUT index is FCh.

MOD1 DAC = 7Bh + 4 x 2Ah = 123h = 291

Figure 6. Recommended RC Filter for DAC Outputs in Voltage

Mode and Current Sink Mode

Figure 5. Low-Voltage Hysteresis Example

DS1876

DAC

3.24k

Ω

3.24k

Ω

0.01µF

VOLTAGE OUTPUT

DS1876

DAC

Ω

0.1µF

CURRENT SINK

2kΩ

VPOA

VPOD

VCC

SEE

RECALLED VALUE

PRECHARGED

TO 0

PRECHARGED

TO 0

PRECHARGED TO 0

SEE RECALL

DS1876 Datasheet(PDF) 16 Page - Maxim Integrated Products

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