a8292 Allegro MicroSystems, Inc., a8292 Datasheet - Page 8

• Manufacturer Part Number: a8292
• Description: Dual Lnb Supply And Control Voltage Regulator
• Manufacturer: Allegro MicroSystems, Inc.

Table 1. Detection Thresholds for Tone Generation Options
A8292
In-rush Current
At start-up or during an LNB reconfiguration event, a tran-
sient surge current above the normal DC operating level can
be provided by the A8292. This current increase can be as high
as 900 mA, typical, for as long as required, up to a maximum
of 48 ms. The 8292 can also provide up to 700 mA per chan-
nel individually, or 1.1 A to both channels simultaneously, for a
period of up to 2 s. Operating at this level for a longer period is
not recommended.
Tone Detection
A 22 kHz tone detector is provided in each channel of the A8292
solution. The detector extracts the tone signal and provides it as
an open-drain signal on the TDO pins. The maximum tone out
error is ±1 tone cycle, and the maximum tone out delay with
respect to the input is 1 tone cycle. Detection thresholds are given
in table 1.
Tone Generation
The A8292 solution offers four options for tone generation,
providing maximum flexibility to cover every application. The
EXTM pins (external modulation), in conjunction with the I
control bits: TMODE (tone modulation) and TGATE (tone gate),
provide the necessary control. The TMODE bit controls whether
the tone source is either internal or external (via the EXTM pin).
Guaranteed
Threshold
Threshold
Detection
Rejection
TMODE
TGATE
(Fig. 1)
(mV
(mV
Option
EXTM
PP
PP
)
)
Control
400
100
0/1
1
1
1
Control
400
100
0/1
2
1
1
Transmit
continuous
Control
22 kHz
signal,
logic
300
100
0/1
3
0
Dual LNB Supply and Control Voltage Regulator
Control
22 kHz
signal
gated
logic
300
100
4
0
1
n.a.
300
100
must be 0 to
prevent tone
transmission
At least one
0
Receive
n.a.
400
100
2
1
C™
Both the EXTM pin and TGATE bit determine the 22 kHz con-
trol, whether gated or clocked.
that when using option 4, when EXTM stops clocking, the LNB
volts park at the LNB voltage, either plus or minus half the tone
signal amplitude, depending on the state of EXTM. For example,
if the EXTM is held low, the LNB DC voltage is the LNB pro-
grammed voltage minus 325 mV (typical).
Figure 1. Options for tone generation
Option 1 – Use internal tone, gated by the TGATE bit.
Option 2 – Use internal tone, gated by the EXTM pin.
Option 3 – Use external tone, gated by the TGATE bit.
Option 4 – Use external tone.
Four options for tone generation are shown in figure 1. Note
TMODE
TMODE
TMODE
TMODE
EXTM
TGATE
Tone
(LNB Ref)
TGATE
Tone
(LNB Ref)
TGATE
Tone
(LNB Ref)
TGATE
Tone
(LNB Ref)
EXTM
EXTM
EXTM
115 Northeast Cutoff, Box 15036
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 [phone]
www.allegromicro.com
LNB (V)
LNB (V)
LNB (V)
LNB (V)
8