THS6012_16 Datasheet, PDF (17/37 Pages) Texas Instruments – 500-mA DUAL DIFFERENTIAL LINE DRIVER

THS6012
www.ti.com
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 -V_CC pins from both drivers must always be at the same potential.
– Driver 2 is powered down by simply opening the +V_CC 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:
ǒ Ǔ ^{ǒ Ǔ ǒ Ǔ} PD ≅ 2 VCC ICC ) VCC _ VO
VO
RL
Where:
P_D = Power dissipation for one amplifier
V_CC = Split supply voltage
I_CC = Supply current for that particular amplifier
V_O = Output voltage of amplifier
R_L = Load resistance
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 V_CC voltage. One last
note, which is often overlooked: the feedback resistor (R_F) 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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