A8291 Datasheet, PDF (1/19 Pages) Allegro MicroSystems – Single LNB Supply and Control Voltage Regulator

A8291
Single LNB Supply and Control Voltage Regulator
Features and Benefits
▪ 2-wire serial I²C™ -compatible interface: control (write) and
status (read)
▪ LNB voltages (16 programmable levels) compatible with
all common standards
▪ Tracking switch-mode power converter for lowest dissipation
▪ Integrated converter switches and current sensing
▪ Provides up to 500 mA load current
▪ Static current limit circuit allows full current at startup and
13→18 V output transition; reliably starts wide load range
▪ Push-pull output stage minimizes 13→18 V and 18→13 V
output transition times for highly capacitive loads
▪ Adjustable rise/fall time via external timing capacitor
▪ Built-in tone oscillator, factory-trimmed to 22 kHz
facilitates DiSEqC™ tone encoding, even at no-load
▪ Four methods of 22 kHz tone generation, via I²C™ data
bits and/or external pin
▪ Filter bypass MOSFET minimizes losses during tone transmit
▪ 22 kHz tone detector facilitates DiSEqC™ 2.0 decoding
▪ Auxiliary modulation input
▪ LNB overcurrent with timer
▪ Diagnostics for output voltage level, input supply UVLO,
and DiSEqC™ tone output
▪ Cable disconnect diagnostic
Package:
28 pin 5 mm × 5mm
MLP/QFN (suffix ET)
Description
Intended for analog and digital satellite receivers, this single
low noise block converter regulator (LNBR) is a monolithic
linear and switching voltage regulator, specifically designed to
provide the power and the interface signals to an LNB down
converter via coaxial cable. The A8291 requires few external
components, with the boost switch and compensation circuitry
integrated inside of the device. A high switching frequency is
chosen to minimize the size of the passive filtering components,
further assisting in cost reduction. The high levels of component
integration ensure extremely low noise and ripple figures.
The A8291 has been designed for high efficiency, utilizing
the Allegro^® advanced BCD process. The integrated boost
switch has been optimized to minimize both switching and
static losses. To further enhance efficiency, the voltage drop
across the tracking regulator has been minimized.
The A8291 has integrated tone detection capability, to support
full two-way DiSEqC™ communications. Several schemes
are available for generating tone signals, all the way down
to no-load, and using either the internal clock or an external
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VS
VREG
C3
220 nF
VDD
R1 R2 R3 R4 R5 R6
EXTM
BFC
TDO
SDA
SCL
ADD
IRQ
C1
100 nF
Regulator
DAC
I² C™-
Compatible
Interface
Functional Block Diagram
L1
33 μH D1
L3
1 MH
C2
100 μF
VIN
C5
100 μF
LX GNDLX
C6
1 μF
C4
100 nF
BOOST VCP
Boost
Converter
Charge BFC
Pump
VPump
fsw
LNB
Voltage
Control
EXTM
TMode
Wave
Shape
Linear
Stage
TCAP
Fault Monitor
TGate
fsw
OCP
PNG
TSD
VUV
Clock
Divider 22 kHz
Oscillator
TDO
Tone
Detect
PAD
GND
D2
B
BFO
BFI
R10 B
17
C12 C
R7
15 7
LNB
L2
220 μH
C8
D3 ₂₂₀ nF
R9
30 7
TCAP
C7
22 nF
C11
0.68 μF
A
TDI _R8
100 7
C10
10 nF
D5
B
VOUT
C13
C9
D4
10 nF 220 nF
B
C
A ^{R9-C11 network is needed only when a highly}
inductive load is applied, such as ProBand LNB.
B _{D2, D4, D5, and R10 are used for surge protection.}
C Either C12 or C9 should be used, but not both.
8291-DS, Rev. 14