DS1876 datasheet(14/69 Pages) MAXIM

14 / 69 page

Maxim Integrated

SFP Controller with Dual LDD Interface

DS1876

corresponding alarms and warnings (TXP HI1, TXP LO1,

TXP HI2, TXP LO2, BIAS HI1, and BIAS HI2) are asserted

or deasserted.

After resetting, the device completes one QT cycle

before making comparisons. The TXP LO quick-trip

alarm updates its alarm bit, but does not create FETG

until after TXDEXT. TXP HI and BIAS HI can also be con-

figured to wait for TXDEXT; however, this can be disabled

using QTHEXT_ (Table 02h, Register 88h).

Monitors and Fault Detection

Monitors

Monitoring functions on the DS1876 include six quick-

trip comparators and six ADC channels. This monitoring

combined with the alarm enables (Table 01h/05h) deter-

mines when/if the DS1876 turns off DACs and triggers

the TXFOUT and TXDOUT1, TXDOUT2 outputs. All the

monitoring levels and interrupt masks are user program-

mable.

Six Quick-Trip Monitors and Alarms

Six quick-trip monitors are provided to detect potential

laser safety issues and LOS status. These monitor the

following:

1) High Bias Current 1 (HBATH1), causing QT BIAS1 HI

2) Low Transmit Power 1 (LTXP1), causing QT TXP1 LO

3) High Transmit Power 1 (HTXP1), causing QT TXP1 HI

4) High Bias Current 2 (HBATH2), causing QT BIAS2 HI

5) Low Transmit Power 2 (LTXP2), causing QT TXP2 LO

6) High Transmit Power 2 (HTXP2), causing QT TXP2 HI

The high and low transmit power quick-trip registers

(HTXP1, HTXP2, LTXP1, and LTXP2) set the thresholds

used to compare against the PMON1 and PMON2 volt-

ages to determine if the transmit power is within speci-

fication. The HBATH1 and HBATH2 QTs compare the

BMON1 and BMON2 inputs (generally from the laser

driver’s bias monitor output) against their threshold set-

tings to determine if the present bias current is above

specification. The bias and power QTs are routed to

FETG through interrupt masks to allow combinations

of these alarms to be used to trigger FETG. The bias

and power QTs are directly connected to TXFOUT (see

Figure 9). The user can program up to eight different

temperature-indexed threshold levels for HBATH1 and

HBATH2 (Table 06h, Registers E0h

-E7h).

Six ADC Monitors and Alarms

The ADC monitors six channels that measure tem-

perature (internal temp sensor), VCC, PMON1, PMON2,

BMON1, and BMON2 using an analog multiplexer to

measure them round-robin with a single ADC (see the

ADC Timing section). The channels have a customer-

programmable full-scale range, and all channels have a

customer-programmable offset value that is factory pro-

grammed to a default value (see Table 2). Additionally,

PMON1, PMON2 and BMON1, BMON2 can right-shift

results by up to 7 bits before the results are compared

to alarm thresholds or read over the I2C bus. This allows

customers with specified ADC ranges to calibrate the

ADC full scale to a factor of 1/2n of their specified range

to measure small signals. The DS1876 can then right-

shift the results by n bits to maintain the bit weight of their

specification.

Figure 3. Quick-Trip Sample Timing

Table 2. ADC Default Monitor Full-Scale Ranges

QUICK-TRIP SAMPLE TIMES

LTXP2

SAMPLE

HBIAS1

SAMPLE

HBIAS1

SAMPLE

HBIAS2

SAMPLE

HTXP1

SAMPLE

HTXP2

SAMPLE

LTXP1

SAMPLE

LTXP2

SAMPLE

tREP

QT CYCLE

SIGNAL (UNITS)

+FS SIGNAL

+FS HEX

-FS SIGNAL

-FS HEX

Temperature (NC)

127.996

7FFF

-128

8000

VCC (V)

6.5528

FFF8

0000

PMON1, PMON2 and BMON1, BMON2 (V)

2.4997

FFF8

0000

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