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ACS102A Schematic ( PDF Datasheet ) - Semtech Corporation

Teilenummer ACS102A
Beschreibung ACS102A Fiber Modem
Hersteller Semtech Corporation
Logo Semtech Corporation Logo 




Gesamt 13 Seiten
ACS102A Datasheet, Funktion
www.DataSheet4U.com
ACS102A Fiber ModemAdvanced Communications
ACS102A Data Sheet
Features
* Full duplex serial transmission over single/twin fiber.
* Link lengths up to 25km.
* Supports asynchronous data rates from DC to 162kbps.
* Full diagnostic modes - Remote and Local loopback.
A* Ultra low power consumption, typically 2-3mA, which could be
extracted from the RS-232 port for self powered applications.
2* Uses a single Ping Pong LED or Laser Duplex Device for single fiber
0applications, low cost LED/PIN or Laser/PIN combinations for twin
fiber applications.
1* Additional operating mode to support PIN with integrated TIA.
* Supports 3 additional low frequency asynchronous channels or
Sthe RS-232 handshake signals.
* Digital and differential voltage input modes, plus modes for non
Cfiber applications - RF
A 2* Bit Error Rate (BER) < 10-9
* Available in 44 pin TQFP (part no: ACS102A-TQ) and 44 pin
PLCC (part no: ACS102A-PL) packages.
TRC PPLED
LDD
LED/PIN
Laser/PIN
Digital
Data
FIFO Time
3B4B
combinations
TxD
Filter
Compress
Compress
Encoder
LED/Laser
Driver
RxD
Digital
Data
FIFO Time
3B4B
Filter
D ecom pr ess
D ecom pr ess
Decoder
LED/PIN
Receiver
RS-232 Interface
Control Logic
DCDB CTS DSR RIO RTS DTR RII
DR(3:1) DM(3:1) HD(2:1) DP HBT ERL PORB
Equivalent Block Diagram of ACS102A
Description
The ACS102A is a complete controller, driver and receiver IC, supporting full-
duplex asynchronous transmission from DC to 162kbps over a single serial link.
Although primarily designed for single optical fibre applications, any other simple
serial media may be used. The ACS102A is optimised for very low power
consumption, consuming only 2 - 3mA at RS-232 data rates including power
provided to the LED and 'heartbeat' monitor. In applications where the power is
extracted from the RS232 data lines, this leaves a generous amount of power left
for any power extraction and RS-232 level shifting circuitry.
The ACS102A employs data compression and time compression techniques,
affording high launch power in short bursts, leading to a low average power
consumption. The advantage of this approach is that high link budgets can be
achieved with inexpensive optical components.
For example, the recommended set-up for RS-232 applications (19.2kbps +
handshake signals) assumes that the LED is driven with a peak current of
approximately 15.4mA for 6 % of the time. The machine cycle is short enough to
facilitate power supply smoothing with a small external capacitor in the region of
100µF.
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ACS102A Datasheet, Funktion
Advanced Communications
ACS102A Data Sheet
The HBT pin is active High and can supply up to 16 mA at a voltage of
> VDD - 0.5 Volts. The display LED should be placed between the
HBT pin and GND with a series resistor. The resistor value is a
function of the efficiency of the display LED, and the power budget.
Example: Calculating the HBT resistor value
LED on voltage:
VDD (ACS102A):
Resistor voltage:
Current to LED:
Resistor value:
Average current:
Average power:
2.0V
5.0V
3.0V
2mA (high efficiency LED)
3/2*10-3 = 1500
64µA
0.32mW
Note: The LED referred to in this section is of the inexpensive display
type and should not be confused with the LED that interfaces with the
fiber optic cable itself.
Power consumption considerations
The power consumption of the ACS102A is a function of the
following:
component is dependent on the XTAL frequency while the static
component is dependent on static current loads. (See Calculating
average current and power consumption for details).
Since the peak current can be very much greater than the average
current, it is important to use a substantial smoothing capacitor on
VA+ and VD+. The recommended values are at least 47µF* for
VD+ and 100µF* for VA+. The configuration can be seen in Figure 1.
(* Capacitor tolerance +/- 20 %)
Data delay and skew
The Full Duplex Delay (FDD) through the system, which applies to
TxD à RxD, RTS à CTS and DTR à DSR, is shown in Table 5.
DR3
0
1
1
1
1
DR2
1
0
0
1
1
DR1
1
0
1
0
1
FDD
6.5ms
3.8ms
2.8ms
2.3ms
2.0ms
Table 5. FDD with XTAL = 10MHz
i. The sample-clock DR(1:3)
ii. The transmit current setting (TRC)
iii. Handshake signals frequency
The FDD is inversely proportional to the XTAL frequency and may
be calculated for other XTALs using the formula below:
iv. XTAL frequency
v. Supply voltage
FDDXTAL = (10 7 / XTAL) * FDD10MHz
2 The sample-clock
The skew between the main TxD data channel and handshake
signals is 1 - 2 data bits as long as the maximum handshake data-
The sample-clock selected by DR(1:3), see section headed Data-
rate of 2kbps is respected. For handshake frequencies above
Rate Selection, determines the quantity of data transmitted over the
2kbps, the skew will be proportional to the handshake signal
fiber link. The 'transmit' window opens once each frame and closes
frequency.
when the time compress FIFO is empty. The 'receive' window is
aligned with the 'transmit' window of the far-end modem, and tracks
LED considerations & Suppliers
the 'transmit' window such that it closes on detection of the last data
bit. Clearly, the lower the sample-clock the smaller the active time
and the lower the power consumption.
Since LEDs from different suppliers may emit different
wavelengths, it is recommended that the LEDs in a communicating
pair of modems are obtained from the same supplier. The
The transmit current setting
ACS102A can support any wavelength LED or LASER.
Furthermore, the emission spectrum is a function of temperature,
The formula given in section headed LED current control, relates to
so a temperature difference between the ends of a link reduces the
the peak current delivered to the LED. The average current however
responsivity of the receiving LED, resulting in a reduction in the link
is very much lower. The DC balanced nature of data encoding means
budget. Information is given in the suppliers’ data sheets. The
the LED consumes current for approximately 50 % of the 'transmit'
following manufacturers have components that will be tested with
window time. The average current delivered to the LED is therefore a
the ACS102A and Acapella will be glad to assist with contact
function of both the peak current and the duration of the 'transmit'
names and addresses on request:
window.
MITEL
(e.g. 1A-212ST, 1A-212SMA)
Handshake signals frequency
Acapella
GCA
(e.g. A-ST, A-SMA)
(e.g. 1A-212-ST-05, 1A-212-SM-02)
Handshake data which is interleaved with the main data channel is
Honeywell
(e.g. HFE4214-013, HFE4404-013)
generated and written to the time compress FIFO each time a change
is detected on either RTS or DTR. The power consumption is lower
Power Supply Decoupling
when the signals change at low frequency or are held at a DC level. It
is possible to limit the power consumption dedicated to the
handshake signals by limiting the frequency of operation using
HD(1:2) input pins. See section headed RS-232 Handshake Signals.
The ACS102A 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 LED or PIN. The modem should have an
XTAL frequency
independent power trace to the point where power enters the board.
The ACS102A uses CMOS technology and therefore the power
consumption is proportional to the frequency of switching.
Consequently, the effect of reducing the value of the XTAL alone will
result in lower power consumption. However, the current component
delivered to the LED and sourced from outputs such as RxD and HBT
are static and as such are independent of the XTAL frequency.
Figures 4 to 6 all show the recommended power supply decoupling.
The LED/PIN/LASER should be sited very close to the PINP, PINN,
LAN and LAP pins. A generous ground plane should be provided,
especially around the sensitive PINP, PINN, LAN and LAP pins. The
modem should be protected from EMI/RFI sources in the standard
ways.
It is worth noting that a modem pair configured with an XTAL of
10MHz and a sample-clock of XTAL/40 will yield the same
performance as a modem pair configured with an XTAL of 5MHz and
a sample-clock of XTAL/20. However, the modem pair with the lower
value XTAL is likely to consume the higher power with a higher data
delay (see section headed Data delay and skew). This is because,
although the dynamic power has reduced, the higher sample-clock
leads to a much longer active time, a factor which dominates the
overall power calculation.
Current and Power Consumption
The average current consumption may be split into two components;
the dynamic component and the static component. The dynamic
Link Budgets
The link budget is the difference between the power coupled to the
fiber via the transmit LED and the power required to realise the
minimum input-amplifier current via the receive LED/PIN. The link
budget is normally specified in dB or dBm, and represents the
maximum attenuation allowed between communicating 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 LED performance. The power coupled to the cable, is
a function of the efficiency of the LED, the current applied to the LED
and the type of the fiber optic cable employed. The conversion
current produced by the reverse biased LED is a function of the LED
efficiency and the fiber type.
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ACS102A pdf, datenblatt
Advanced Communications
ACS102A Data Sheet
ACS102A_PLCC
2
Figure 6. Basic Circuit for a Twin Fiber Link using LASER and PIN.
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