THS6022 Datasheet, PDF (22/38 Pages) Texas Instruments – 250-mA DUAL DIFFERENTIAL LINE DRIVER

THS6022
250-mA DUAL DIFFERENTIAL LINE DRIVER
SLOS225C – SEPTEMBER 1998 – REVISED JANUARY 2000
independent power supplies (continued)
However, with independent power supply pins for each device, the effects of crosstalk through common
impedance in the power supplies are 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 THS6022 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.
• Individual amplifiers are powered down by simply opening the +V_CC connection.
The THS6022 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
ǒ Ǔ ₎ ǒ Ǔ _{ǒ Ǔ} ^{calculations are best achieved through actual measurements. For small loads, however, internal power}
dissipation for each amplifier in the THS6022 can be approximated by the following formula:
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 = RMS output voltage of amplifier
R_L = Load resistance
To find the total THS6022 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.
device protection features
The THS6022 has two built-in features that protect the device against improper operation. The first protection
mechanism is output current limiting. Should the output become shorted to ground the output current is
automatically limited to the value given in the data sheet. While this protects the output against excessive
current, the device internal power dissipation increases due to the high current and large voltage drop across
the output transistors. Continuous output shorts are not recommended and could damage the device.
Additionally, connection of the amplifier output to one of the supply rails (±V_CC) can cause failure of the device
and is not recommended.
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