LNB Supply and Control Voltage Regulator

A8285 and

A8287

11

Allegro MicroSystems, LLC

115 Northeast Cutoff

Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

Bit 5 (ENB). When set to 1, enables the LNB output. When set to

0, the LNB output is disabled.

(typically 500 mA) is selected. When set to 1, the higher limit

(typically 700 mA), is selected.

Bit 7 (ENT). When set to 1, enables modulation of the LNB out-

compatible with the 400 kHz transfer speed, this bit may be used

to encode DiSEqC™ 2.0 tone bursts for communication with the

LNB or switcher at the far end of the coaxial cable.

. The main fault condi-

tions: overcurrent, undervoltage, and overtemperature, are all

indicated by setting the relevant bit in the Status register. In

all fault cases, once the bit is set it is not reset until the A8285/

output is also indicated by DIS. DIS and PNG are the only bits

sequence of the master in a fault condition is to detect the fault by

reading the Status register, then rereading the Status register until

the status bit is reset, indicating the fault condition has been reset.

The fault may be detected by: continuously polling, responding

to an interrupt request (IRQ), or detecting a fault condition exter-

nally and performing a diagnostic poll of all slave devices. Note

that the fully operational condition of the Status register is all 0s.

This simplifies checking of the status byte.

Bit 0 (TSD). A 1 indicates that the A8285/A8287 has detected an

overtemperature condition and has disabled the LNB output. DIS

is set and the A8285/A8287 does not re-enable the output until

so instructed by writing the relevant bit into the Control register.

The status of the overtemperature condition is sampled on the ris-

ing edge of the ninth clock pulse in the data read sequence. If the

condition is no longer present, then the TSD bit is reset, allowing

the master to re-enable the LNB output if required. If the condi-

tion is still present, then the TSD bit remains at 1.

Bit 1 (OCP) Overcurrent. If the A8285/A8287 detects an over-

current condition for greater than the detection time, and if ODT

is enabled, the LNB output is then disabled. Also, the OCP bit is

set to indicate that an overcurrent has occurred, and the DIS bit is

set. The Status register is updated on the rising edge of the ninth

clock pulse. The OCP bit is reset in all cases, allowing the master

to re-enable the LNB output. If the overcurrent timer is not

enabled, the A8285/A8287 operates in current limit indefinitely,

and the OCP bit is not set.

Bit 2 and 3. Reserved.

Bit 4 (PNG) Power Not Good. Set to 1 when the LNB output is

enabled and the LNB output volts are below 85% of the pro-

grammed LNB voltage. The PNG is reset when the LNB volts

are within 90% of the programmed LNB voltage.

Bit 5 (DIS) LNB output disabled. DIS is used to indicate the

current condition of the LNB output. At power-on, or if a fault

condition occurs, the disable bit is set. Having this bit change to

1 does not cause the IRQ to activate because the LNB output may

at the end of a write sequence, if the LNB output is enabled.

Bit 6. Reserved.

Bit 7 (VUV) Undervoltage lockout. Set to 1 to indicate that the

been, below the minimum level and that an undervoltage lockout

has occurred, which has disabled the LNB output. Bit 5 also is

set, and the A8285/A8287 does not re-enable the output until so

instructed (by having the relevant bit written into the Control reg-

ister). The status of the undervoltage condition is sampled on the

rising edge of the ninth clock pulse in the data read sequence. If

the condition is no longer present, the VUV bit is reset, allowing

the master to re-enable the LNB output if required. If the condi-

tion is still present, the VUV bit remains set to 1.

Bit

Name

Function

0

VSEL0

See Output Voltage Amplitude

Selection Table

1

VSEL1

2

VSEL2

3

VSEL3

0: LNBx = Low range

1: LNBx = High range

4

ODT

0: Overcurrent disable time off

1: Overcurrent disable time on

5

ENB

0: Disable LNB Output

1: Enable LNB Output

6

ILIM

0: Overcurrent Limit = 500mA

1: Overcurrent Limit = 700mA

7

ENT

0: Disable Tone

1: Enable 22KHz internal tone

Control (Write) Register Table