Rainbow Electronics DS1876 - Manual (Page 13)

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DS1876
SFP Controller with Dual LDD Interface
only difference is that the DS1876 already has deter-
mined the present temperature, so the t
INIT time is not
required for the DS1876 to recall the APC and MOD
set points from EEPROM. See Figure 1.
DACs as a Function of Transmit Disable
(TXD1, TXD2)
If TXD1 or TXD2 are asserted (logic 1) during normal
operation, the associated outputs are disabled within
t
OFF . When TXD1 or TXD2 are deasserted (logic 0), the
DS1876 sets the DACs with the value associated with
the present temperature. When asserted, soft TXD1 or
soft TXD2 (TXDC) (Lower Memory, Register 6Eh) would
allow a software control identical to the TXD1 or TXD2 pin
(Figure 2). The POLARITY register (Table 02h, Register
C6h) determines if the off-state value of the DACs is
V
REFIN
or 0V.
Quick-Trip Timing
As shown in Figure 3, the DS1876’s input compara-
tor is shared among the six quick-trip alarms (TXP1
HI, TXP1 LO, TXP2 HI, TXP2 LO, BIAS1 HI, and BIAS2
HI). The comparator polls the alarms in a multiplexed
sequence. The updates are used to compare the HTXP1,
LTXP1, HTXP2, and LTXP2 (monitor diode voltages) and
the HBATH1 and HBATH2 (BMON1, BMON2) signals
against the internal APC and BIAS reference, respec-
tively. Depending on the results of the comparison, the
Table 1. Acronyms
Figure 1. Power-Up Timing
Figure 2. TXD1, TXD2 Timing
V CC
V POA
DAC
SETTINGS
HIGH IMPEDANCE OFF STATE LUT VALUE
500µs t INIT
t
OFF
t
ON
TXD_
DAC
SETTINGS
LUT VALUE LUT VALUE OFF STATE
ACRONYM DESCRIPTION
ADC Analog-to-Digital Converter
AGC Automatic Gain Control
APC Automatic Power Control
APD Avalanche Photodiode
ATB Alarm Trap Bytes
DAC Digital-to-Analog Converter
LOS Loss of Signal
LUT Lookup Table
NV Nonvolatile
QT Quick Trip
TE Tracking Error
TIA Transimpedance Amplifier
ROSA Receiver Optical Subassembly
SEE Shadowed EEPROM
SFF Small Form Factor
SFF-8472
Document Defining Register Map of SFPs
and SFFs
SFP Small Form Factor Pluggable
SFP+ Enhanced SFP
TOSA Transmit Optical Subassembly
TXP Transmit Power