DS1862AB Просмотр технического описания (PDF) - Maxim Integrated

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DS1862AB

XFP Laser Control and Digital Diagnostic IC

Maxim Integrated 

XFP Laser Control and Digital Diagnostic IC

Monitor Channels

The DS1862A has seven monitored voltage signals that

are polled in a round-robin multiplexed sequence and

are updated with the frame rate, tFRAME. All channels

are read as 16-bit values, but have 13-bit resolution,

and with the exception of temperature measurements,

all channels are stored as unsigned values. The resulting

16-bit value for all monitored channels, except internal

temperature, is calculated by internally averaging the

analog-to-digital result eight times. The resulting internal

temperature monitor channel is averaged 16 times. See

the Internal Calibration section for a complete descrip-

tion of each channel’s method(s) of internal calibration.

The AUX1MON, AUX2MON, and VCC2/3 monitor chan-

nels are optional and can be disabled. This feature

allows for shorter frame rate for the essential monitor

channels. Channels that cannot be disabled are inter-

nal temperature, BMD, RSSI, and IBIASMON. A table of

full-scale (FS) signal values (using factory internal cali-

bration without right shifting) and the resulting FS code

values for all seven channels is provided in Table 4.

Measuring Temperature—Internal or External

The DS1862A is capable of measuring temperature on

three different monitor channels: internal temperature

sensor, AUX1MON, and AUX2MON. Only the internal

temperature and AUX2MON channels are capable of

indexing the LUT to control the extinction ratio. To use

an external temperature sensor on AUX2MON, the

TEMP_INT/EXT bit in Table 04h, Byte 8Bh, must be set.

While AUX2MON controls the extinction ratio, the inter-

nal temperature sensor does not stop running; despite

extinction ratio control by AUX2MON, it is this internal

temperature signal that continues to control the status

of temperature flags. Also, when TEMP_INT/EXT = 1,

the internal temperature clamps at -40°C and

+103.9375°C, and when TEMP_INT/EXT = 0 it clamps at -

120°C and +127.984°C. AUX2MON, however, does have

its own flag to indicate an out-of-tolerance condition and

assert the INTERRUPT pin.

Both AUX1MON and AUX2MON can be used to mea-

sure temperature as a function of voltage on their

respective pins. They can be enabled by selecting

either 0h or 4h from Table 5. Internal (or external) cali-

bration may be required to transmute the input voltage

to the desired two’s-complement digital code, readable

from the result registers in lower memory, Bytes 6Ah,

6Bh, 6Ch, 6Dh.

Measuring VCC2/3

The DS1862A has the flexibility to internally measure

either VCC2 or VCC3 to monitor supply voltage. VCC2 or

VCC3 is user selectable by the VCC2/3_SEL bit in Table

01h, Byte DCh. To remove VCC2/3 from the round-robin

monitor update scheme, despite having VCC2 or VCC3

selected to be monitored, the Reserve_EN bit in Table

04h, Byte 8Bh can be programmed to a 0. The analog

power-on-reset flag, POA, indicates the status of VCC3

power supply. Even though POA seems to behave simi-

larly to VCC2/3 monitor channel, it is completely sepa-

rate and has no connection.

RESERVE_EN

0

0

1

1

VCC2/3_SEL

0

1

0

1

RESULT

VCC2/3 result not enabled.

VCC2/3 result not enabled.

VCC3 is being measured.

VCC2 is being measured.

Measuring APC and Laser Parameters—BMD,

IBIASMON, RSSI

BMD and BIASSET are used to control and monitor the

laser functionality. Regardless of the set BMD current in

the APC register, the DS1862A measures BMD pin cur-

rent and uses this value not only to adjust the current

on the BIASSET pin, but also to monitor TX-P as well.

The IBIASMON pin is used to input a voltage signal to

the DS1862A that can be used to monitor the bias cur-

rent through the laser. This monitor channel does not

drive the HIGH BIAS quick-trip (QT) alarms for safety

Table 4. Monitor Channel FS and LSB Detail

SIGNAL

Temperature

VCC2/3

IBIASMON

RSSI

AUX1MON

AUX2MON

BMD (TX-P)

+FS SIGNAL

127.984°C

6.5528V

2.4997V

2.4997V

6.5528V

6.5528V

1.5mA

+FS (hex)

7FF8

FFF8

FFF8

FFF8

FFF8

FFF8

FFF8

-FS SIGNAL

-120°C

0V

0V

0V

0V

0V

0mA

-FS (hex)

8800

0000

0000

0000

0000

0000

0000

LSB

0.0625°C

100μV

38.147μV

38.147μV

38.147μV

38.147μV

22.888nA

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