a8291 Allegro MicroSystems, Inc., a8291 Datasheet - Page 12

• Manufacturer Part Number: a8291
• Description: A8291 Single Lnb Supply And Control Voltage Regulator
• Manufacturer: Allegro MicroSystems, Inc.

A8291
Bit 0
Bit 1
Bit 2
Bit 3
Bit 4
Bit 5
Bit 6
Bit 7
TMODE Tone Mode. Selects between the use of an external 22 kHz logic signal or the use of
TGATE Tone Gate. Allows either the internal or external 22 kHz tone signals to be gated,
CADT
–
–
BFC2
I0
I1
Single LNB Supply and Control Voltage Regulator
the internal 22 kHz oscillator to control the tone generation on the LNB output. A 0
selects the external tone and a 1 selects the internal tone. See the Tone Generation
section for more information
unless the EXTM is selected for gating. When set to 0, the selected tone (via
TMODE) is off. When set to 1, the selected tone is on. See Tone Generation Section
for more information.
Cable Disconnect Test. To perform this test, set bits CADT, ENB, and VSEL0
through VSEL3 through the I
linear regulator is disabled, a 1 mA current source between the BOOST output and
the LNB output is enabled, and the BOOST voltage is increased to 22.8 V. After
these conditions are set, if the LNB voltage is above 21 V, it is assumed that the
coaxial cable connection between the LNBR output and the LNB head has been dis-
connected. In this case, the CAD bit is set in the status register. If there is a load on
the LNB pin, then the LNB voltage will decrease proportionally to the load current.
If the LNB volts drop below 19.95 V, it is assumed that the coax cable is connected
and the CAD bit in the status register is set to 0.
Not Used.
Not Used.
Bypass MOSFET Control. When set to 1, the internal bypass MOSFETs are en-
abled. A 0 disables the bypass MOSFETs.
Address.
Address.
Table 3. Control Register Address (I1, I0) = 10 and 11
Bit
0
1
2
3
4
5
6
7
TMODE
TGATE
Name
CADT
BFC2
I0
I1
-
-
2
C™-compatible interface. During this test, the LNB
0: Cable Disconnect Test Off
1: Cable Disconnect Test On
0: Bypass MOSFET Off
1: Bypass MOSFET On
1: Tone Gated On
0: Tone Gated Off
0: External Tone
1: Internal Tone
Address Bit: 0
Address Bit: 1
Function
Not Used
Not Used
115 Northeast Cutoff, Box 15036
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 [phone]
www.allegromicro.com
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