Rainbow Electronics DS1862 - Manual (Page 18)

DS1862
XFP Laser Control and Digital Diagnostic IC
18 ____________________________________________________________________
fault functionality, current on the BIASSET pin is moni-
tored by the DS1862 to control the HIGHBIAS quick
trip. Similar to TX-P, the RSSI pin is used to measure
the received power, RX-P.
Measuring Voltage Quantities
using AUX1MON and AUX2MON
AUX1MON and AUX2MON are auxiliary monitor inputs
that may be used to measure additional parameters.
AUX1/2MON feature a user-selectable register that
determines the measured value’s units (i.e., voltage,
current, or temperature). In addition to indicating units,
some of the 4-bit op-codes, in Table 5, also place the
part in special modes used for alarms and faults inter-
nally. Whichever units’ scale is selected, the DS1862 is
only capable of measuring a positive voltage quantity,
therefore internal or external calibration may be
required to get the binary value to match the measured
quantity. A table of acceptable units and/or their corre-
sponding user-programmable 4-bit op-code is provid-
ed below.
Alarms and Warning Flags
Based on Monitor Channels
All of the monitor channels feature alarm and warning
flags that are asserted automatically as user-pro-
grammed thresholds are internally compared with mon-
itor channel results. Flags may be set, which, if not
masked, will generate an interrupt on the
INTERRUPT
pin or generate a safety fault. Whenever V CC2/3 ,
AUX2MON, AUX1MON, RSSI, and internal temperature
go beyond their threshold trip points and the corre-
sponding mask bit is 0, an interrupt is generated on the
INTERRUPT pin and a corresponding warning or alarm
flag is set. Similarly, a safety fault occurs whenever
BMD or BIASSET go beyond threshold trip points.
When this happens, the FETG pin immediately asserts
and BIASSET and MODSET currents are shut down.
Monitor Channel Conversion Example
Table 6 provides an example of how a 16-bit ADC code
corresponds to a real life measured voltage using the
factory-set calibration on either RSSI or IBIASMON. By
factory default, the LSB is set to 38.147µV.
To calculate V CC2 , V CC3 , AUX1MON, or AUX2MON,
convert the unsigned 16-bit value to decimal and multi-
ply by 100µV.
To calculate the temperature (internal), treat the two’s-
complement value binary number as an unsigned bina-
ry number, then convert it to decimal and divide by
256. If the result is grater than or equal to 128, subtract
256 from the result.
Temperature: high byte = -128°C to +127°C signed;
low byte = 1/256°C.
Table 5. AUX1/2MON Functionality
Selection (Unit Selection)
VALUE
DESCRIPTION OF AUX1/2MON INTENDED USE
(UNITS OF MEASURE)
0000b Auxiliary monitoring not implemented
0001b
APD bias voltage (16-bit value is voltage in units of
10mV)
0010b Reserved
0011b
TEC current (mA), (16-bit value is current in units of
0.1mA)
0100b
Laser temperature (same encoding as module
temperature)
0101b Laser wavelength
0110b
+5V supply voltage (encoded as primary voltage
monitor)
0111b
+3.3V supply voltage (encoded as primary voltage
monitor)
1000b
+1.8V supply voltage (encoded as primary voltage
monitor) (V
CC2 )
1001b
-5.2V supply voltage (encoded as primary voltage
monitor)
1010b + 5V sup p l y cur r ent ( 16- b i t val ue i s cur r ent i n 0.1m A)
1101b
+3.3V supply current (16-bit value is current in
0.1mA)
1110b
+1.8V supply current (16-bit value is current in
0.1mA)
1111b
-5.2V supply current (16-bit value is current in
0.1mA)
Table 6. A/D Conversion Example
MSB (BIN) LSB (BIN) VOLTAGE (V)
11000000 00000000 1.875
10000000 10000000 1.255
Table 7. Temperature Bit Weights
S 2 6 2 5 2 4 2 3 2 2 2 1 2 0
2 -1 2 -2 2 -3 2 -4 2 -5 — — —