THS6212 Datasheet, PDF (35/48 Pages) Texas Instruments – Differential, Line-Driver Amplifier

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THS6212
SBOS758 – MAY 2016
The two output stages used to drive the load of Figure 85 are shown as an H-Bridge in Figure 88. The average
current drawn from the supply into this H-Bridge and load is the peak current in the load given by Equation 13
divided by the crest factor (CF) for the signal modulation. This total power from the supply is then reduced by the
power in R_T, leaving the power dissipated internal to the drivers in the four output stage transistors. That power is
simply the target line power used in Equation 8 plus the power lost in the matching elements (R_M). In the
following examples, a perfect match is targeted giving the same power in the matching elements as in the load.
The output stage power is then set by Equation 17.
P_OUT =
I_P
CF
´
V
CC
-
2P
L
(17)
The total amplifier power is then given by Equation 18:
P_TOT = I_Q ´ V_CC +
I_P
CF
´ V_CC - 2P_L
(18)
For the example given by Figure 84, the peak current is 159 mA for a signal that requires a crest factor of 5.6
with a target line power of 20.5 dBm into a 100-Ω load (115 mW).
With a typical quiescent current of 21 mA and a nominal supply voltage of ±12 V, the total internal power
dissipation for the solution of Figure 84 is given by Equation 19:
P_TOT
=
21
mA
(24
V)
+
159 mA
5.6
(24
V)
-
2(115
mW)
=
955
mW
(19)
8.3 Do's and Don'ts
8.3.1 Do
• Include a thermal design at the beginning of the project.
• Use well-terminated transmission lines for all signals.
• Use solid metal layers for the power supplies.
• Keep signal lines as straight as possible.
• Use split supplies where required.
8.3.2 Don't
• Use a lower supply voltage than necessary.
• Use thin metal traces to supply power.
• Forget about the common-mode response of filters and transmission lines.
9 Power Supply Recommendations
The THS6212 is designed to operate optimally using split power supplies. The device has a very wide supply
range of ±5 V to ±14 V to accommodate many different application scenarios. Choose power-supply voltages
that allow for adequate swing on both the inputs and outputs of the amplifier to prevent affecting device
performance. The ground pin provides the ground reference for the control pins and must be within V_S– to (V_S+ –
5 V) for proper operation.
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