8281
AND
8282
A8282SLB
NC
OLF
VBULK
NC
NC
GND
GND
SENSE
LNB
LX
VIN
TCAP
1
2
3
24
23
22
EXTM
VINT
PUMPX
VPUMP
CPUMP
GND
GND
ENT
EN
VSEL0
VSEL1
LLC
LNB SUPPLY AND
CONTROL-VOLTAGE REGULATORS
Intended for analog and digital satellite receivers, these low-noise
block converter regulators (LNBRs) are monolithic linear and switching
voltage regulators specifically designed to provide the power and
interface signals to the LNB down converter via the coaxial cable. If the
device is in standby mode (EN terminal low), the regulator output is
disabled, allowing the antenna down converters to be supplied or
controlled by other satellite receivers sharing the same coaxial cable. In
this mode, the device will limit the output reverse current.
The A8281SLB output is set to 13 or 18
-
V by the VSEL terminal. It
is supplied in a 16-lead SOIC power-tab package. The power tabs are at
ground potential and need no electrical isolation.
The A8282SLB output is 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 compensate for the voltage drop in the coaxial cable (LLC
terminal high). It is supplied in a 24-lead SOIC power-tab package.
The power tabs are at ground potential and need no electrical isolation.
The A8282SLB is an improved version of the A8283SLB, without a
bypass switch.
Data Sheet
27448.2c
CHARGE
PUMP
BUCK
REG.
4
5
6
7
8
9
9
10
11
12
21
20
19
18
17
16
15
14
13
VOLTAGE
CONTROL
Dwg. PP-072-2
FEATURES
s
LNB selection and standby function
s
Built-in tone oscillator factory trimmed to 22
-
kHz, facilitates
DiSEqC™ (a trademark of EUTELSAT) encoding
s
Tracking switch-mode power converter for lowest dissipation
s
Externally adjustable short-circuit protection
s
LNB short-circuit protection and diagnostics
s
Auxiliary modulation input
s
Internal over-temperature protection
s
Reverse-current protection
s
Cable length compensation (A8282SLB only)
ABSOLUTE MAXIMUM RATINGS
at T
A
= +25
°
C
Supply Voltage, V
IN
...........................
47-V
Output Current, I
LNB
....
Internally Limited
Output Voltage Range, V
LNB
..
-1-V to +22-V
Logic Input Voltage Range,
V
I
...................................
-0.3-V to +7-V
Flag Output Voltage, V
OLF
...................
7-V
Operating Temperature Range,
T
A
.................................
-20
°
C to +85
°
C
Junction Temperature, T
J
................
+150
°
C
Storage Temperature Range,
T
S
..............................
-55
°
C to +150
°
C
These devices incorporate features that have patents pending.
Always order by complete part number, e.g.,
A8282SLB
.
8281
AND
8282
LNB SUPPLY AND
CONTROL-VOLTAGE REGULATORS
FUNCTIONAL BLOCK DIAGRAM
and typical application
100
µH
0.1
µF
CPUMP
PUMPX
0.1
µF
VPUMP
VIN
100
µF
LX
100
µF
VINT
(A8282 ONLY)
4.7
µF
VOLTAGE
REG.
CHARGE
PUMP
–
BOOST
VOLTAGE
BUCK
CONV.
–
+
OVER-
CURRENT
EN
5V
176 kHz
7V
VREF
–
+
135 mV
+
352 kHz
VBULK
SENSE
+
V
IN
47 V MAX
R
S
200 mΩ
+
DiSEqC TERMINATION
+
+
–
LNB
5 kΩ
100 nF
÷2
ENT
25 kΩ
–
900 mV
15
Ω
180
µH
0.22
µF
÷8
&
WAVESHAPING
22 kHz TONE
EXTM
TSD
OLF
OVER-
CURRENT
5 kΩ
1 kΩ
0.1
µF
LLC
(A8282
ONLY)
VSEL0
(A8282
ONLY)
VSEL1
TCAP
10 nF
Dwg. FP-051-2
A8281SLB
A8281SLB Output Voltage Select Table
VSEL1
L
H
V
LNB
13 V
18 V
EXTM
OLF
VBULK
GND
SENSE
LNB
LX
VIN
1
CHARGE
PUMP
16
15
14
13
12
11
10
9
PUMPX
VPUMP
CPUMP
GND
ENT
EN
VSEL1
TCAP
2
3
4
5
6
7
8
BUCK
REG.
A8282SLB Output Voltage Select Table
VSEL0
L
L
L
L
H
H
H
H
VSEL1
L
L
H
H
L
L
H
H
LLC
L
H
L
H
L
H
L
H
V
LNB
13 V
14 V
18 V
19 V
12 V
13 V
20 V
21 V
VOLTAGE
CONTROL
Dwg. PP-072-3
2
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
Copyright © 2003 Allegro MicroSystems, Inc.
8281
AND
8282
LNB SUPPLY AND
CONTROL-VOLTAGE REGULATORS
ELECTRICAL CHARACTERISTICS: unless otherwise noted at T
J
< 125°C, C
LNB
= 0.1 µF,
4.5
-
V + V
LNB
< V
IN
< 47
-
V
Limits
Characteristic
Supply Voltage Range
Output Voltage Error
(reference Output Voltage
Select table)
Output Reverse Current
Buck Switch On Resist.
Buck Switch Current Limit
Switching Frequency
Linear Reg. Volt. Drop
Logic Input Voltage
Logic Input Current
Supply Current
Tone Characteristics
Tone Frequency
Tone Amplitude
Tone Duty Cycle
Tone Rise or Fall Time
External Modulation
Tone Amplitude
External Modulation Input
Voltage Range
External Modulation Input
Impedance
f
tone
V
tone(PP)(ENT)
dc
tone
t
r
, t
f
ENT = H
ENT = H, 12 mA
≤
I
LNB
≤
750 mA
ENT = H, 12 mA
≤
I
LNB
≤
750 mA
ENT = H, 12 mA
≤
I
LNB
≤
750mA
20
400
40
5
400
22
650
—
10
550
24
900
60
15
800
kHz
mV
%
µs
mV
Symbol
V
IN
E
VLNB
Operating
6 mA
≤
I
LNB
≤
750 mA, ENT = L
12 mA
≤
I
LNB
≤
750 mA, ENT = H,
average V
LNB
I
RLNB
r
DS(on)
I
BSM
f
O
∆V
BUCK
V
IL
V
IH
I
IH
I
IN
V
IH
= 5 V
Outputs disabled (EN = L)
EN = H, I
LNB
= 0
16 x f
tone
V
SENSE
– V
LNB
, ENT = L, I
LNB
= 750 mA
EN = L, V
LNB
= 22 V, V
IN
= 22 V or
fl
oating
T
J
= 25°C, I
LNB
= 750 mA
T
J
= 125°C, I
LNB
= 750 mA
Test Conditions
Min.
4.5 +V
LNB
—
—
—
—
—
1
320
700
—
2
—
—
—
Typ.
—
0
0
1
0.57
0.84
—
352
900
—
—
<1.0
0.25
6
Max.
47
±4.5
±4.5
5
0.67
0.94
2.5
384
1100
0.8
—
10
1
10
Units
V
%
%
mA
Ω
Ω
A
kHz
mV
V
V
µA
mA
mA
V
tone(PP)(EXTM)
f = 22 kHz square wave, I
LOAD
= 12 mA to
450 mA, V
IN
= 100mV to 125 mV;
V
PP
ac coupled
V
EXTM(PP)
Z
EXTM
AC coupled
f = 22 kHz
100
4
—
—
125
10
mV
kΩ
continued next page
NOTES: 1. Typical data is for design information only.
2. Negative current is defined as coming out of (sourcing) the specified device terminal.
www.allegromicro.com
3
8281
AND
8282
LNB SUPPLY AND
CONTROL-VOLTAGE REGULATORS
ELECTRICAL CHARACTERISTICS: unless otherwise noted at T
J
≤
125
°
C, C
LNB
= 0.1
-
µ
F,
4.5
-
V + V
LNB
≤
V
IN
≤
47
-
V.
Limits
Characteristic
Protection Circuitry
Current-Limiting Threshold
Overload Flag Output Low
Overload Flag Leakage Current
Thermal Shutdown Temp.
Thermal Shutdown Hysteresis
V
ILNB(th)
V
OLF
I
OLF
T
J
∆T
J
V
BULK
– V
SENSE
I
OLF
= 8
-
mA
V
OLF
= 5.5
-
V
115
—
—
—
—
135
0.28
<1.0
165
20
155
0.5
10
—
—
mV
V
µA
°C
°C
Symbol
Test Conditions
Min.
Typ.
Max.
Units
NOTES: 1. Typical data is for design information only.
2. Negative current is defined as coming out of (sourcing) the specified device terminal.
4
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
8281
AND
8282
LNB SUPPLY AND
CONTROL-VOLTAGE REGULATORS
FUNCTIONAL DESCRIPTION
Buck regulator.
A current-mode buck converter
provides the linear regulator a supply voltage that
tracks the selected LNB output voltage. The buck
converter operates at 16 times the internal tone fre-
quency, nominally 352-kHz.
The tracking regulator provides minimum power
dissipation across the range of output voltages by
adjusting the SENSE terminal voltage, nominally
900-mV above the LNB output voltage. The tracking
regulator also provides adequate headroom for tone
injection.
Linear regulator.
The output linear regulator will
sink or source current. This allows tone modulation
into a capacitive load of 0.1
-µ
F over the output
current range of 12
-
mA to 750
-
mA.
Slew rate control.
The programmed output volt-
age rise and fall times can be set by an external
capacitor (with an internal 25
-
kΩ resistor) located on
the TCAP terminal. The range of acceptable capaci-
tor values is 4.7
-
nF to 47
-
nF. This feature only
affects the turn-on and programmed voltage rise and
fall times. Modulation is unaffected by the capacitor.
If LNB output voltage rise and fall time limiting is
not required, the TCAP terminal should use a 100
-
nF
ceramic as a default value to minimize output noise.
If a small value capacitor is used, the rise time will be
limited by the time required to charge the VBULK
capacitor.
Short-circuit limit regulator.
The LNB output is
current limited. The short-circuit protection threshold
is set by the value of an external resistor, R
S
, in
conjunction with an internal 135-mV reference
voltage (V
ILNB(th)
).
R
S
= 0.135/I
LNBM
where I
LNBM
is the desired current-limit value. The
sense resistor should be chosen based on the maxi-
mum dc plus ac (tone) load current required, internal
V
ILNB(th)
tolerance, and sense resistor accuracy. For
750-mA applications, a precision 140-mΩ resistor is
recommended. For 500-mA applications, the resistor
value can be raised to 200-mΩ.
In operation, the short-circuit protection produces
current limiting at the input due to the tracking con-
verter. If the output is shorted, the linear regulator
will limit the output current to I
LNBM
.
Fault output.
Short-circuit or thermal shutdown
will cause the OLF terminal, an open-drain diagnostic
output flag, to go LOW.
Internal tone modulation.
The ENT (tone enable)
terminal activates the internal tone signal, modulating
the dc output with a 650
-
mV peak-to-peak trapezoidal
waveform. The internal oscillator is factory trimmed
to provide a tone of 22
-
kHz. No further adjustment is
required. Burst coding of the tone can be accom-
plished, due to the fast response of the ENT input and
rapid tone response. This allows implementation of
the DiSEqC™ protocols.
External tone modulation.
To improve design
flexibility and to allow implementation 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 terminal. The
peak-to-peak input amplitude should stay within
100
-
mV to 125
-
mV to ensure the DiSEqC amplitude
specification over the output current range. If exter-
nal modulation is not used, the EXTM terminal
should be decoupled to ground with a 0.1
-µ
F ceramic
capacitor.
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5
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