ds1861 Maxim Integrated Products, Inc., ds1861 Datasheet - Page 20

• Manufacturer Part Number: ds1861
• Description: Ds1861 Full Laser Control With Fault Management
• Manufacturer: Maxim Integrated Products, Inc.

Full Laser Control with Fault Management
The default setting of ER = 1Ch corresponds to N = 30,
which is the minimum useable value. The maximum
useable value is N = 136 (ER = E8h). For more informa-
tion refer to the Automatic Extinction Ration Control
section.
• MODLOAD.....<R/W><NV><0000h> This register
determines the startup value of I
falling edge of TX-D when MODLOAD_Enable = 1 and
no fault condition has occurred. This 12-bit register
value is left justified in a 16-bit register. The 4 LSBs
default to 0s.
• Control.....<R/W><NV><70h> This byte is used to
enable/disnable the shutdown alarms and configure
several other settings. Writing to this byte causes an
EEPROM write cycle, even if only the HALT bit (SRAM)
is changed. It should not be modified more than the
specified number of write cycles.
20
0. HALT.....Setting this bit high stops the control
1. Excite_Disable.....Setting this bit high prevents
2. Soft_TX-Disable.....This bit is ORed with the TX-D
3. DPOL.....Diode Polarity. Set to 0 to have the
4. HBIAS_Enable.....Set high to allow a safety fault
____________________________________________________________________
loop and freezes the outputs at their present
state. Once the control loop is stopped the I
and I
This bit is SRAM and resets to zero when V
drops below V
the DS1861 from entering the excitation state (it
does not add the disturbance current), which
disables automatic extinction ratio control. I
will remain at its last value until reset by a
fault or set to MODLOAD.
pin to create the internal TX-Disable signal. So
asserting either Soft_TX-Disable or the TX-D pin
will disable the outputs. Both Soft_TX-Disable
and TX-D must be deasserted for the outputs to
operate.
BMD pin source current. Set to 1 to have BMD
sink current.
caused by high bias alarm shut the part down.
MODSET
N
=





ER
ER
POAF
<
<
output registers can be read.
6 0
6 0
:
:
2
.
> +
> +
32
32
RSEL
RSEL
MODSET
=
=
1
0
following a
MODSET
BIASSET
CC
Quick-Trip Monitors
• HTXP Threshold.....<R/W><NV><00h> Sets the
threshold current for the HTXP alarm. The alarm trips
when I
Threshold<2:0>) 0.125]. Set to 00h to disable the alarm.
• LTXP Threshold.....<R/W><NV><00h> Sets the
threshold current for the LTXP alarm. The alarm trips
when I
Threshold<2:0>) 0.125]. Set to 00h to disable the alarm.
• HBIAS Threshold.....<R/W><NV><00h> Sets the
threshold current for the high bias current alarm. The
alarm trips when BIAS current is ≥7.625µA x (HBIAS
Threshold). This register value is compared directly
against the I
determine if an alarm condition has occurred. Set
HBIAS threshold to 00h to disable this alarm.
Password
• PW High and Low.....<R/W><NV><0000h> The PWE
value is compared against the value written to these
locations to determine if the user has write access to
password-protected memory locations. These locations
read as zeros unless the password has been entered
into PWE to ensure the password remains secure.
DAC Codes
• I
signicant byte of the 18-bit I
= 7.625µA x (I
and the password must be entered to read this value.
• I
DAC code. The LSB weight of the I
is 477nA. Thus, I
The part must be halted and the password entered to
read this value. The four least significant bytes of this
register read as 0s.
BIASSET
MODSET
5. LTXP_Enable.....Set high to allow a safety fault
6. HTXP_Enable.....Set high to allow a safety faultl
7. MODLOAD_Enable.....If high, I
caused by low transmitted power alarm shut the
part down.
caused by high transmitted power alarm shut
the part down.
value in MODLOAD on the falling edge of TX-D
when no fault condition is present. Otherwise,
I
prior to when TX-D was asserted.
MODSET
BMD
BMD
Code.....<R/W><V><00h> This is the most
Code.....<R/W><V><0000h> The I
BIASSET
BIASSET
> I
< I
will return to operation with its value
MODSET
BMD SETPOINT
BMD SETPOINT
code value in register D1h to
code). The part must be halted
= 477nA x (I
BIASSET
DAC code. I
MODSET
MODSET
· [1 + (HTXP
· [1 - (LTXP
MODSET
DAC code
loads the
MODSET
BIASSET
code).