AK2574VB AKM [Asahi Kasei Microsystems], AK2574VB Datasheet - Page 20

• Manufacturer Part Number: AK2574VB
• Description: 156M Laser Diode Driver + APC for Burst Mode
• Manufacturer: AKM [Asahi Kasei Microsystems]

3. Alarm
AK2574 has 2 alarm functions as shown in Table 3-1.
Table 3-1 Alarm function
3.1 TXACT
Fig 3-1illustrates TXACT block diagram. TXACT is detected when the PDIN voltage is beyond the reference voltage
Table 3-2 shows the PDIN capacitance (CPDIN) and Table 3-3 shouws the relationship between txact_ref and
The TXACT detection time (t_act) is estimated under the 50% mark data input and average monitor current as
Note: TXACT detection time varies with input data pattern.
Fig 3-1 TXACT block diagram
Fig 3-2 Reference figures for TXACT detection time
<MS0266-E-00>
(txact_ref), and TXACT is held during BRST = “H”. The txact_ref is set with RE_DAC_TXACT. TXACT detection
time depends on the Monitor PD current (i_pd) and capacitance (CMPD), external resistor (RPD), AK2574 PDIN
capactance (CPDIN) and txact_ref voltage (see Fig 3-2 for the reference).
RE_DAC_TXACT. The polarity of TXACT can be set by RE_TXACT_POL (0: “H” at detection, 1: “L” at detection).
follows:
t
ALM
TXACT
CLKALM
Monitor
_
i_pd
i_pd
PD
act
RPD
RPD
RPD
PDIN
When the PDIN voltage (monitor PD current) is
beyond the reference voltage (txact_ref). TXACT is
kept once TXACT detection until BRST=”L”.
When the detected 0s or 1s sequential CLK input
(100ns typical).
AK2574 goes into “Shutdwon”.
Detection condition
( *
i_pd @ DATA=1
0 @ DATA=0
CPDIN
CMPD
CMPD
CPDIN
(TXACT)
When detected CLKALM,
DAC
CPDIN
* )
txact_ref
vpd
LN
1 (
txact_ref
COMP
RPD
txact
-20-
*
comp_out
i
COMP
BRST
_
_
Release condition
BRST=”L”
Polarity of CLK is
changed
ref
pd
2 /
)
RESET
SET/
comp_out
Detected Time
Depens on the condition.
See “3.1 TXACT” for more
100ns (typ)
200ns (max)
information
AND
TXACT
2003/12