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PDF A8284SB Data sheet ( Hoja de datos )
| Número de pieza | A8284SB | |
| Descripción | TWO-OUTPUT LNB SUPPLY AND CONTROL-VOLTAGE REGULATOR | |
| Fabricantes | Allegro MicroSystems | |
| Logotipo |  |
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8284
ADVANCE INFORMATION
(Subject to change without notice)
December 22, 2000
TWO-OUTPUT LNB SUPPLY AND
CONTROL-VOLTAGE REGULATOR
Intended for analog and digital satellite receivers, the low noise block
A8284SLB
converter regulator (LNBR) is a monolithic linear and switching voltage
regulator designed to provide power and interface signals to the LNB
OSEL 1
24 EXTM
downconverter via the coaxial cable. Because most satellite receivers have two
antenna ports, the output voltage of the regulator is available at one of two
OLF 2
23 VINT
logic-selectable output terminals (LNBA, LNBB). If the device is in stand-by
mode (EN terminal LOW), both regulator outputs are disabled, allowing the
VBULK 3
22 PUMPX
antenna downconverters to be supplied and controlled by other satellite
LNBB 4
YNC 5
GND 6
RGND 7
OSENSE 8
TLNBA 99
CLX 10 BUCK
AVIN 11
FTCAP 12
REG.
21 VPUMP
20 CPUMP
19 GND
18 GND
17 ENT
16 EN
15 VSEL0
14 VSEL1
13 LLC
TDwg. PP-072-1A
CNote that the A8284SB (dual in-line package)
and A8284SLB (small-outline IC package) are
Aelectrically identical and share a common
terminal number assignment.
NTABSOLUTE MAXIMUM RATINGS
Supply Voltage, VIN .......................... 47 V
OOutput Current, IO .... Internally Limited
CLogic Input Voltage Range,
receivers sharing the same coaxial cable. Similar single-output devices, with a
bypass function for slave operation in single-dish dual-receiver systems, are the
A8283SB/SLB.
The regulator outputs are set to 12, 13, 18, or 20 V by the VSEL terminals.
Additionally, it is possible to increase the selected voltage by 1 V to compen-
sate for the voltage drop in the coaxial cable (LLC terminal HIGH).
The LNBR combines a tracking switching regulator and low-noise linear
regulators. Logic inputs (VSEL0, VSEL1, and LLC) select the desired output
voltage. A tracking current-mode buck converter provides the linear regulator
input voltage that is set to the output voltage plus typically 0.8 V. This
maintains constant voltage drop across the linear regulators while permitting
adequate voltage range for tone injection.
The device is supplied in a 24-pin plastic DIP with batwing tabs
(A8284SB), or a 24-lead SOIC power-tab package (A8284SLB). In both cases,
the power tab is at ground potential and needs no electrical isolation.
FEATURES
I Complete Interface for Two LNBs Remote Supply and Control
I LNB Selection and Stand-By Function
I Built-In Tone Oscillator Factory Trimmed to 22 kHz, Facilitates
DiSEqC™ (a trademark of EUTELSAT) Encoding
I Full Modulation With No Load
I Tracking Switch-Mode Power Converter for Lowest Dissipation
I Externally Adjustable Short-Circuit Protection
I LNB Short-Circuit Protection and Diagnostics
I Auxiliary Modulation Input
I Cable Length Compensation
I Internal Over-Temperature Protection
VI ................................... -0.5 V to +7 V
Flag Output Voltage, VOLF .................. 7 V
This device incorporates features that have patents pending.
Operating Temperature Range,
TA ............................... -20°C to +85°C
Storage Temperature Range,
TS ............................. -40°C to +150°C
Always order by complete part number, e.g., A8284SLB .
1 page  
8284
TWO-OUTPUT LNB SUPPLY AND
CONTROL-VOLTAGE REGULATOR
FUNCTIONAL DESCRIPTION
The ENT (Tone Enable) terminal activates the internal
tone signal, modulating the dc output with a ±0.3 V, 22
kHz symmetrical waveform. The internal oscillator is
factory trimmed to provide a tone of 22 kHz ± 2 kHz. No
further adjustment is required. The internal oscillator
operates the buck converter at 16 times the tone fre-
quency.
Burst coding of the 22 kHz tone can be accomplished,
due to the fast response of the ENT input and rapid tone
response. This allows implementation of the DiSEqC™
protocols.
To improve design flexibility and to allow implemen-
tation of proposed LNB remote control standards, an
analog modulation input terminal is available (EXTM).
An appropriate dc blocking capacitor must be used to
couple the modulating signal source to the EXTM termi-
nal. If external modulation is not used, the EXTM termi-
nal can be left open.
The output linear regulators will sink and source
current. This feature allows full modulation capability
into capacitive loads as high as 0.25 µF.
The programmed output voltage rise and fall times
can be set by an internal 25 kΩ resistor and an external
capacitor located on the TCAP terminal. Although any
value of capacitor is permitted, practical values are
typically 0.001 µF to 0.02 µF. This feature only affects
the turn on and programmed voltage rise and fall times.
Modulation is unaffected by the choice of TCAP. This
terminal can be left open if voltage rise and fall time
control is not required.
Two terminals are dedicated to the over-current
protection/monitoring: SENSE and OLF. The LNB output
is current limited. The short-circuit protection threshold is
set by the value of an external resistor, RS, between
terminals 3 and 8. RS = VOM(th)/IOM where VOM(th) is the
current-limiting threshold voltage and IOM is the desired
current limit value. The minimum recommended value
for RS is 0.17 Ω.
In operation, the short-circuit protection produces
current fold-back at the input due to the tracking con-
verter. If the output is shorted the linear regulator will
limit the output current to IOM. The tracking converter
will maintain a constant voltage drop of 0.8 V across the
linear regulator. This condition results in typically 550
mW dissipation (IOM • 0.8 V). Short-circuit or thermal
shutdown activation will cause the OLF terminal, an open-
drain diagnostic output flag, to go LOW.
Thermal resistance:
DIP — RθJA = 40°C/W, RθJT = 6°C/W,
SOIC — RθJA = 55°C/W, RθJT = 6°C/W.
The device junction temperature should be kept below
150°C. Thermal shut-down circuitry turns off the device
if junction temperature exceeds +165°C typically.
The products described here are manufactured under one or more
U.S. patents or U.S. patents pending.
Allegro MicroSystems, Inc. reserves the right to make, from time to
time, such departures from the detail specifications as may be
required to permit improvements in the performance, reliability, or
manufacturability of its products. Before placing an order, the user is
cautioned to verify that the information being relied upon is current.
Allegro products are not authorized for use as critical components
in life-support devices or systems without express written approval.
The information included herein is believed to be accurate and
reliable. However, Allegro MicroSystems, Inc. assumes no responsi-
bility for its use; nor for any infringement of patents or other rights of
third parties which may result from its use.
www.allegromicro.com
5
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| PDF Descargar | [ Datasheet A8284SB.PDF ] | |
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