P

D ≅

2 V

CC

I

CC )

V

CC

_ V

O

V

O

R

L

Where:

PD

= Power dissipation for one amplifier

VCC = Split supply voltage

ICC = Supply current for that particular amplifier

VO

= Output voltage of amplifier

RL

= Load resistance

THS6012

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SLOS226F – SEPTEMBER 1998 – REVISED JUNE 2012

APPLICATION INFORMATION

The THS6012 contains two independent operational amplifiers. These amplifiers are current feedback topology

amplifiers made for high-speed operation. They have been specifically designed to deliver the full power

requirements of ADSL and therefore can deliver output currents of at least 400 mA at full output voltage.

The THS6012 is fabricated using Texas Instruments 30-V complementary bipolar process, HVBiCOM. This

process provides excellent isolation and high slew rates that result in the device's excellent crosstalk and

extremely low distortion.

INDEPENDENT POWER SUPPLIES

Each amplifier of the THS6012 has its own power supply pins. This was specifically done to solve a problem that

often occurs when multiple devices in the same package share common power pins. This problem is crosstalk

between the individual devices caused by currents flowing in common connections. Whenever the current

required by one device flows through a common connection shared with another device, this current, in

conjunction with the impedance in the shared line, produces an unwanted voltage on the power supply. Proper

power supply decoupling and good device power supply rejection helps to reduce this unwanted signal. What is

left is crosstalk.

However, with independent power supply pins for each device, the effects of crosstalk through common

impedance in the power supplies is more easily managed. This is because it is much easier to achieve low

common impedance on the PCB with copper etch than it is to achieve low impedance within the package with

either bond wires or metal traces on silicon.

POWER SUPPLY RESTRICTIONS

Although the THS6012 is specified for operation from power supplies of ±5 V to ±15 V (or singled-ended power

supply operation from 10 V to 30 V), and each amplifier has its own power supply pins, several precautions must

be taken to assure proper operation.

1. The power supplies for each amplifier must be the same value. For example, if the driver 1 uses ±±15 volts,

then the driver 2 must also use ±15 volts. Using ±15 volts for one amplifier and ±5 volts for another amplifier

is not allowed.

2. To save power by powering down one of the amplifiers in the package, the following rules must be followed.

–

The amplifier designated driver 1 must always receive power. This is because the internal startup circuitry

uses the power from the driver 1 device.

–

The -VCC pins from both drivers must always be at the same potential.

–

Driver 2 is powered down by simply opening the +VCC connection.

The THS6012 incorporates a standard Class A-B output stage. This means that some of the quiescent current is

directed to the load as the load current increases. So under heavy load conditions, accurate power dissipation

calculations are best achieved through actual measurements. For small loads, however, internal power

dissipation for each amplifier in the THS6012 can be approximated by the following formula:

To find the total THS6012 power dissipation, we simply sum up both amplifier power dissipation results.

Generally, the worst case power dissipation occurs when the output voltage is one-half the VCC voltage. One last

note, which is often overlooked: the feedback resistor (RF) is also a load to the output of the amplifier and should

be taken into account for low value feedback resistors.

Copyright © 1998–2012, Texas Instruments Incorporated

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