MIC3003 Datasheet, PDF (25/75 Pages) Micrel Semiconductor – FOM Management IC with Internal Calibration

Micrel, Inc.
MIC3003
Figure 3. Internal Calibration RX Power Linear Approximation
C/ Reading the ADC Result Registers
The ADC result registers should be read as 16-bit
registers under internal calibration while under external
calibration they should be read as 8-bit or 16-bit
registers at the MSB address. For example, TX power
should be read under internal calibration as 16 bits at
address A2h: 66h–67h and under external calibration as
8 bits at address A2h: 66h. 9-bit temperature results and
12-bit receive power results should always be read as
16-bit quantities.
Reading the result registers using two-byte burst reads on
the SMBus guarantees that the two bytes are coherent
with each other—that is, they form a matched result pair.
If the two bytes were read separately, it is possible that
the internal result could be updated between the reads,
leading to an incorrect ADC result.
RXPOT
A programmable, non-volatile digitally controlled
potentiometer is provided for adjusting the gain of the
receive power measurement signal chain in the analog
domain. Five bits in the RXPOT register are used to set
and adjust the position of potentiometer. RXPOT
functions as a programmable divider or attenuator. It is
adjustable in steps from 1:1 (no divider action) down to
1/32 in steps of 1/32. If RXPOT is set to zero, then the
divider is bypassed completely. There will be no scaling
of the input signal, and the resistor network will be
disconnected from the VRX pin. At all other settings of
RXPOT, there will be a 32kΩ (typical) load seen on
VRX.
Figure 4. RXPOT Block Diagram
Laser Diode Bias Control
The MIC3003 can be configured to generate a constant
bias current using electrical feedback, or regulate
average transmitted optical power using a feedback
signal from a monitor photodiode, as shown in Figure 5.
An operational amplifier is used to control laser bias
current via the VBIAS output. The VBIAS pin can drive a
maximum of ±10mA. An external bipolar transistor
provides current gain. The polarity of the op amp’s
output is programmable with BIASREF (bit-5 in
OEMCFG1) in order to accommodate either NPN or
PNP transistors that drive common anode and common
cathode laser, respectively. Additionally, the polarity of
the feedback signal is programmable for use with either
common-emitter or emitter-follower transistor circuits.
November 2009
25
M9999-111209-C
[e-mail] or [phone]