M02097-11 Datasheet, PDF (19/21 Pages) M/A-COM Technology Solutions, Inc. – 3.3/5V LED Driver / Limiting Amplifier for Operation to 500 Mbps

Functional Description
3.2
Internal Regulator
When operating from a 5V supply (V_CC connected to +5V), an internal regulator provides a voltage of
approximately 3.3V to the majority of the on-chip circuitry. The on-chip regulator is internally compensated,
requiring no external components. When a 3.3V supply is used (V_CC connected to 3.3V, or both V_CC and V_CC3
connected to 3.3V), internal logic configures the device for 3.3V operation and the regulator is switched to a low-
resistance mode. The device decides whether or not the internal regulator is enabled using internal sensing logic,
the sensing logic also determines whether the device safety circuitry needs to monitor for proper +5V supply
voltage.
3.3
Driver Inputs
The inputs to the data buffer are self-biased through resistors to an internal reference of approximately V_CC - 1.3V.
Both CML and PECL input signals can be AC coupled to the M02097. AC coupling is recommended when using
the internal regulator (V_CC = 5V), though external level-shifting may be used if DC coupling is desired with 5V
supply.
3.4
Driver Output Stage
The output stage incorporates feedback to maintain performance over the range of LED modulation current. The
output stage is nominally configured to drive an output load of ~5Ω with shunt RC compensation for LEDs. OUTP
should be connected directly to the LED cathode. This will result in the optimum pulse response while allowing the
maximum modulation current to be achieved when the output is DC coupled to the load. The LED driver output
stage is separately grounded from the rest of the circuitry (through GNDO) for optimum performance and control of
output characteristics.
The output can also be AC coupled to the LED. LED modulation current is controlled by adjusting current at
MOD_SET. The modulation current can be temperature compensated by setting slope through the TC_SLOPE pin and
TC_START sets the temperature at which the temperature compensation begins to operate.
3.5
Safety Circuitry
Comparators at PB_SET, MOD_SET, PB_OUT OUTP, and C_PB will assert the FAIL output, indicating that a fault condition
has occurred. This condition is latched and requires DIS to be toggled or power cycling before reset occurs. SV_CC
is opened during a fault or disable condition.
By setting DIS high, the bias and modulation output currents are disabled. DIS will disable LED bias and
modulation current if left floating. DIS must be forced to a low state to enable the outputs. When safety circuit
bypass (SCB) mode is enabled, FAIL will indicate a fault condition, but the outputs will not be disabled under a fault
condition. Only the DIS pin will shutdown the outputs when in SCB mode.
02097-DSH-001-C
Mindspeed Technologies^®
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