A8282SLBTR-T Datasheet A8281SLB, A8282SLB, A8282SLBTR | P4-P6

8281

AND

8282

LNB SUPPLY AND

CONTROL-VOLTAGE REGULATORS

115 Northeast Cutoff, Box 15036

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

ELECTRICAL CHARACTERISTICS: unless otherwise noted at T

≤ 125°C, C

LNB

= 0.1-µF,

4.5

-V + V

LNB

≤ V

≤ 47-V.

Limits

Characteristic Symbol Test Conditions Min. Typ. Max. Units

Protection Circuitry

Current-Limiting Threshold V

ILNB(th)

BULK

– V

SENSE

115 135 155 mV

Overload Flag Output Low V

OLF

= 8-mA — 0.28 0.5 V

Overload Flag Leakage Current I

OLF

= 5.5-V — <1.0 10 µA

Thermal Shutdown Temp. T

— 165 — °C

Thermal Shutdown Hysteresis ∆T

—20—°C

NOTES: 1. Typical data is for design information only.

2. Negative current is defined as coming out of (sourcing) the specified device terminal.

8281

AND

8282

LNB SUPPLY AND

CONTROL-VOLTAGE REGULATORS

www.allegromicro.com

Buck regulator. A current-mode buck converter

provides the linear regulator a supply voltage that

tracks the selected LNB output voltage. The buck

converter operates at 16 times the internal tone fre-

quency, nominally 352-kHz.

The tracking regulator provides minimum power

dissipation across the range of output voltages by

adjusting the SENSE terminal voltage, nominally

900-mV above the LNB output voltage. The tracking

regulator also provides adequate headroom for tone

injection.

Linear regulator. The output linear regulator will

sink or source current. This allows tone modulation

into a capacitive load of 0.1-µF over the output

current range of 12-mA to 750-mA.

Slew rate control. The programmed output volt-

age rise and fall times can be set by an external

capacitor (with an internal 25-kΩ resistor) located on

the TCAP terminal. The range of acceptable capaci-

tor values is 4.7-nF to 47-nF. This feature only

affects the turn-on and programmed voltage rise and

fall times. Modulation is unaffected by the capacitor.

If LNB output voltage rise and fall time limiting is

not required, the TCAP terminal should use a 100-nF

ceramic as a default value to minimize output noise.

If a small value capacitor is used, the rise time will be

limited by the time required to charge the VBULK

capacitor.

Short-circuit limit regulator. The LNB output is

current limited. The short-circuit protection threshold

is set by the value of an external resistor, R

, in

conjunction with an internal 135-mV reference

voltage (V

ILNB(th)

= 0.135/I

LNBM

where I

LNBM

is the desired current-limit value. The

sense resistor should be chosen based on the maxi-

mum dc plus ac (tone) load current required, internal

ILNB(th)

tolerance, and sense resistor accuracy. For

750-mA applications, a precision 140-mΩ resistor is

recommended. For 500-mA applications, the resistor

value can be raised to 200-mΩ.

In operation, the short-circuit protection produces

current limiting at the input due to the tracking con-

verter. If the output is shorted, the linear regulator

will limit the output current to I

LNBM

Fault output. Short-circuit or thermal shutdown

will cause the OLF terminal, an open-drain diagnostic

output flag, to go LOW.

Internal tone modulation. The ENT (tone enable)

terminal activates the internal tone signal, modulating

the dc output with a 650-mV peak-to-peak trapezoidal

waveform. The internal oscillator is factory trimmed

to provide a tone of 22-kHz. No further adjustment is

required. Burst coding of the tone can be accom-

plished, due to the fast response of the ENT input and

rapid tone response. This allows implementation of

the DiSEqC™ protocols.

External tone modulation. To improve design

flexibility and to allow implementation of proposed

LNB remote control standards, an analog modulation

input terminal is available (EXTM). An appropriate

dc-blocking capacitor must be used to couple the

modulating signal source to the EXTM terminal. The

peak-to-peak input amplitude should stay within

100-mV to 125-mV to ensure the DiSEqC amplitude

specification over the output current range. If exter-

nal modulation is not used, the EXTM terminal

should be decoupled to ground with a 0.1-µF ceramic

capacitor.

FUNCTIONAL DESCRIPTION

8281

AND

8282

LNB SUPPLY AND

CONTROL-VOLTAGE REGULATORS

115 Northeast Cutoff, Box 15036

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

APPLICATIONS INFORMATION

Component selection:

Input capacitor, C

. An electrolytic capacitor

should be located as close to the device VIN terminal

as possible. The input current is a square wave with

fast rise and fall times so the capacitor must be able to

handle the rms current without excessive temperature

rise. The value of this capacitor is not as important as

the ESR. The worst-case current is with maximum

load current, minimum V

, and maximum V

LNB

(highest switch duty cycle). Choose a capacitor with

a ripple current rating greater than

cin

= I

LNB

x 1.2 x V

LNB(max)

IN(min)

Buck inductor, L1. A 100-µH power inductor is

appropriate for all operating conditions. The rated

saturation current of the inductor must be greater than

1.3-A. To maximize efficiency, the dc resistance

should be less than 350-mΩ.

Clamp diode, D1. A Schottky diode is required at

the switching node LX. This diode should be rated at

1.5 times the maximum load current.

Output capacitor, C

BULK

. A low-ESR (<200-mΩ)

electrolytic capacitor is recommended to minimize

the ripple voltage. Less than 50-mV peak-to-peak is a

reasonable goal.

ripple(PP)

= ESR x I

ripple(max)

where

ripple(max)

= V

BULK(min)

x (1 – [V

BULK(min)

IN(max)

]) /

(L1 x 352

kHz).

Output capacitor, C

LNB

. Increasing the output

capacitance, C

LNB

, will attenuate noise. However,

this is limited by the requirement for low cable

capacitance for 22-kHz tone transmission.

Also, because the linear regulator sink current is

limited, high values of output capacitance combined

with low levels of output current can cause overshoot

of the 22-kHz tone. Operating points above the line

in the following graph will not have excessive over-

shoot.

0.5

Dwg. GP-074

1.0 1.5

OUTPUT CAPACITANCE IN µF

100

OUTPUT CURRENT IN mA

125

MINIMAL OVERSHOOT

EXCESSIVE OVERSHOOT

Layout notes:

1. The printed wiring board should use a heavy

ground plane. A two-sided board with ground planes

on both sides of the board is most desirable. Several

copper vias under the device can be used to connect

the ground planes and enhance thermal performance.

2. For optimum electrical and thermal performance,

the device should be soldered directly onto the board.

3. Keep the sense resistor traces as short and as wide

as possible to lower trace resistance.

4. Connect the bypass capacitors as close to the

device as possible. The lower value ceramic capaci-

tors should be closer to the device than the

electrolytics. The supply voltage, V

, should be

decoupled with an electrolytic capacitor placed as

close to the device as possible.

5. Place the TCAP capacitor as close to the device as

possible.

P1-P3 P4-P6 P7-P9 P10-P12 P13-P14

A8282SLBTR-T

Mfr. #:

Buy A8282SLBTR-T

Manufacturer:

Description:

IC REG CONV RECVRS 1OUT 24SOIC

Lifecycle:

New from this manufacturer.

Delivery:

DHL FedEx Ups TNT EMS

Payment:

T/T Paypal Visa MoneyGram Western Union

A8282SLBTR-T

A8282SLBTR-T

Products related to this Datasheet