ACS401 Semtech Corporation, ACS401 Datasheet - Page 6

• Manufacturer Part Number: ACS401
• Description: Optical Modem ic
• Manufacturer: Semtech Corporation

ERC produces a pulse on detection of each coding error. These
pulses may be accumulated by means of an external electronic
counter.
Please note that ERL and ERC detect coding errors and not data
errors, nevertheless because of the complexity of the coding rules
on the ACS401 the absence of detected errors on these pins will
give a good indication of a high quality link.
LASER/LED Considerations
Since LEDs or LASERs from different suppliers may emit different
wavelengths, it is recommended that the LASERs/LEDs in a
communicating pair of modems are obtained from the same
supplier. Furthermore, the emission spectrum is a function of
temperature, so a temperature difference between the ends of a
link reduces the responsivity of the receiving LASER/LED,
resulting in a reduction in the link budget. Information is given in
the suppliers’ data sheets. The following manufacturers have
components that will be tested with the ACS401 and Acapella will
be glad to assist with contact names and addresses on request:
LED Suppliers
ABB-Hafo (e.g.1A-212ST, 1A-212SMA)
Acapella
GCA
Honeywell (e.g.HFE4214-013, HFE4404-013)
Duplex Suppliers
GCA
Siemens
Operating Wavelengths
The ACS401 can support any wavelength LED, ELED or LASER,
from 660 nm through to 1500 nm.
Power Supply Decoupling
The ACS401 contains a highly sensitive amplifier, capable of
responding to extremely low current levels. To exploit this
sensitivity it is important to reduce external noise to a low level
compared to the input signal from the LASER/LED. The modem
should have an independent power trace to the point where power
enters the board.
Figure 3. shows the recommended power supply decoupling. The
LASER/LED should be sited very close to the PINN, LAN and LAP
pins. A generous ground plane should be provided, especially
(e.g.A-ST, A-SMA)
SBM 51214X
(e.g.1A-212-ST-05, 1A-212-SM-02)
90-0359
1
2
3
4
5
6
7
8
9
10 GND
11 CLK9
12 RxD2
13 RxD1
14 XTI
15 XTO
16 GND
17 GND
18 NC
19 VD+
20 VD+
21 TxCL
22 TxD2
23 ERRL
24 TxD1
25 RxCL
26 NC
27 IC
28 DCDB
29 VD+
30 ERRC
31 RxD4
32 XO2
33 XO1
34 RxD3
CKC
SETB
GND
XI1
TxD3
XI2
TxD4
HBT
DCD
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
Figure 1. Top view of 68 PLCC package
NC = Not Connected IC = Internally Connected
ACAPELLA
1-Fiber Modem
ACS401
around the sensitive PINN, LAN and LAP pins. The modem
should be protected from EMI/RFI sources in the standard ways.
Link Budgets
The link budget is the difference between the power coupled to the
fiber via the transmit LASER/LED and the power required to
realise the minimum input amplifier current via the receive
LASER/LED/PIN. The link budget is normally specified in dB or
dBm, and represents the maximum attenuation allowed between
communicating LASER/LEDs. The budget is utilised in terms of
the cable length, cable connectors and splices. It usually includes
an operating margin to allow for degradation in LASER/LED
performance. The power coupled to the cable, is a function of the
e fficiency of the LASER/LED, the current applied to the
LASER/LED and the type of the fiber optic cable employed.
The conversion current produced by the reverse biased
LASER/LED or PIN is a function of the LASER/LED/PIN efficiency
and the fiber type. The conversion efficiency is measured in terms
of its ability to convert the available optical power to current,
known as the responsivity, given in (A/W). Some examples of link
budgets are given in the tables headed, Link Budget Examples.
Digital Mode
The ACS401 may be used as a controller and data buffer which
allows the device to be used with an external amplifier for non-
fiber applications. Check with Acapella for details.
Data delay and skew
The Full Duplex Delay (FDD) of TxD and control signals XI(1:2)
when using the recommended XTAL frequency of 9.216 MHz
(FDD
TxD FDD
TxD FDD
XI FDD
XI FDD
For other XTAL frequencies, the delay is inversely proportional to
the XTAL frequency using the above delays as the constant of
proportionality.
FDD
The synchronous data skew between the main data channels
RxD1, RxD2, RxD3 and RxD4 across the link is zero data-bits.
XTAL
9.216MHz
9.216MHz
9.216MHz
= (9.216 * 10
9.216MHz
9.216MHz
) are as follows:
60
59
58
57
56
55
54
53
52
51
50
49
48
47
46
45
44
6
/ XTAL) * FDD
=
=
=
=
4 ms (‘standard’mode)
8 ms (‘double’ mode)
10 ms (‘standard’mode)
20 ms (‘double’ mode)
DM3
VD+
DM2
DM1
DR1
DP2
DP1
NC
NC
NC
TRC
IC
VA+
LAP
LAN
PINP
PINN 52
CON2 51
CNT
AGND 49
CON1 48
VG+
NC
NC
NC
GND
DP3
GND
PORB 40
DP4
DR4
DR3
GND
DR2
9.216MHz
68
67
66
65
64
63
62
61
60
59
58
57
56
55
54
53
50
47
46
45
44
43
42
41
39
38
37
36
35