MIC3000 Datasheet, PDF (19/68 Pages) Micrel Semiconductor – SFP Management IC

MIC3000
Power ON and Laser Start-Up
When power is applied, the MIC3000 initializes its internal
registers and state machine. This process takes t_POR, about
50µs. Following t_POR, analog-to-digital conversions begin,
serial communication is possible, and the POR bit and data
ready bits may be polled. The first set of analog data will be
available t_CONV after t_POR. MIC3000s are shipped from the
factory with the output enable bit, OE, set to zero, off. The
MIC3000’s power-up default state, therefore, is APC off,
V_BIAS, V_MOD, and SHDN outputs disabled. V_BIAS, V_MOD, and
SHDN will be floating (high impedance) and the laser diode,
if connected, will be off. Once the device is incorporated into
a transceiver and properly configured, the shutdown states of
SHDN, V_BIAS and V_MOD will be determined by the state of the
APC configuration and OE bits. Table 8, Table 9, and Table
10 illustrate the shutdown states of the various laser control
outputs versus the control bits.
Configuration Bits
Shutdown State
OE
SPOL
SHDN
0
Don’t Care
Hi-Z
1
0
≈GND
1
1
≈V_DD
Table 8. Shutdown State of SHDN vs.
Configuration Bits
V_DD
V_POR
t_POR
TXFAULT
t_INIT
t_CONV
TXDISABLE
Micrel
Configuration Bits
V_BIAS Shutdown
State
OE
INV
BIASREF
0
Don’t Care Don’t Care
V_BIAS
Hi-Z
1
Don’t Care
0
≈GND
1
Don’t Care
1
≈V_DD
Table 9. Shutdown State of V_BIAS vs.
Configuration Bits
Configuration Bits
OE
MODREF
0
Don’t Care
V_MOD Shutdown State
V_MOD
Hi-Z
1
0
≈GND
1
1
≈V_DD
Table 10. Shutdown state of V_MOD vs.
Configuration bits
In order to facilitate hot-plugging, the laser diode is not turned
on until t_INIT2 after power-on. Following t_INIT2, and assuming
TXDISABLE is not asserted, the DACs will be loaded with
their initial values. Since t_CONV is much less than t_INIT2, the
first set of analog data, including temperature, is available at
t_INIT2. Temperature compensation will be applied to the DAC
values if enabled. APC will begin if OE is asserted. (If the
output enable bit, OE, is not set, the V_MOD, V_BIAS, and SHDN
outputs will float indefinitely.) Figure 7 shows the power-up
timing of the MIC3000. If TXDISABLE is asserted at power-
up, the V_MOD and V_BIAS outputs will stay in their shutdown
states following MIC3000 initialization. A/D conversions will
begin, but the laser will remain off.
V_DD
V_POR
t_POR
TXFAULT
t_INIT
t_CONV
SHDN⁽¹⁾
/DATA_READY
TXDISABLE
SHDN⁽¹⁾
|V_MOD|
/DATA_READY
|V_BIAS|
|V_MOD|
TX Output
90% nominal output
t_ON(2)
|V_BIAS|
TX Output
(a) MIC3000 Power-On, TXDISABLE not Asserted
(b) MIC3000 Power-On, TXDISABLE Asserted
Notes:
Figure 7. MIC3000 Power-On Timing (OE=1)
1. Polarity programmable; active-high shown.
2. Determined by loop response, e.g., C_COMP.
October 2004
19
M9999-101204