Single LNB Supply and Control Voltage Regulator

A8290

8

Allegro MicroSystems, Inc.

115 Northeast Cutoff, Box 15036

Worcester, Massachusetts 01615-0036 (508) 853-5000

www.allegromicro.com

0

+A

2000 ms

Start-up

Continuous Operation

LNB

Reconfiguration

Short

Circuit

Continuous Operation

900 mA,

typical

700 mA

650 mA

t

Safe Operating Area

Short Circuit Handling

If the LNB output is shorted to ground, the LNB output current

will be clamped to 900 mA, typical. If the short circuit condition

lasts for more than 48 ms, the A8290 will be disabled and the

OCP bit will be set.

Auto-Restart

After a short circuit condition occurs, the host controller should

periodically reenable the A8290 to check if the short circuit has

been removed. Consecutive startup attempts should allow at least

5 s of delay between restarts.

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 A8290. This current increase can be as high as

900 mA, typical, for as long as required, up to a maximum of

48 ms.

DC current

The A8290 can handle up to 700 mA per channel individually,

during continuous operation.

Tone Detection

A 22 kHz tone detector is provided in the A8290 solution. The

detector extracts the tone signal and provides it as an open-drain

signal on the TDO pin. 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 A8290 solution offers four options for tone generation,

providing maximum flexibility to cover every application. The

Table 1. Detection Thresholds for Tone Generation Options

Transmit

Receive

Option

(Fig. 1)

1

2

3

4

n.a.

n.a.

TMODE

1

1

0

0

0

1

TGATE

Control

0/1

1

Control

0/1

1

At least one must

be 0 to prevent

tone transmission

EXTM

1

Control

0/1

22 kHz

logic

signal,

continuous

Control

gated

22 kHz

logic

signal

Guaranteed

Detection

Threshold

400

400

300

300

300

400

Rejection

Threshold

100

100

100

100

100

100

Figure 1. ODT (Overcurrent Disable Timing) Mode Timing Diagram