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THS4509-Q1 Datasheet(PDF) 27 Page - National Semiconductor (TI) |
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THS4509-Q1 Datasheet(HTML) 27 Page - National Semiconductor (TI) |
27 / 40 page ( ) W - - = - + k 50 V V V 2 I S S CM EXT (2) VS+ CM VSignal VS– RF RF RG RG RT RO RO VOUT+ VOUT- THS4509 VBias= VCM RS RT VCM VCM VCM VCM RS V S+ CM V S– 50kW tointernal CMcircuit I EXT 50kW ( ) ÷÷ ø ö çç è æ + - ÷÷ ø ö çç è æ - = + F IN IC F CM S IC PU R 1 R 1 V R 1 V V V R (3) Single-Supply Operation (3 V to 5 V) THS4509-Q1 www.ti.com........................................................................................................................................................................................... SLOS547 – NOVEMBER 2008 performance, but it is intended to be a dc bias input pin. Bypass capacitors are recommended on this pin to reduce noise at the output. The external current required to overdrive the internal resistor divider is given by Equation 2: where VCM is the voltage applied to the CM pin. Figure 84. THS4509 DC-Coupled Single Supply With Input Biased to VCM In Figure 85 the source is referenced to ground and so is the input termination resistor. RPU is added to the circuit to avoid violating the VICR of the op amp. The proper value of resistor to add can be calculated from Equation 3: Figure 83. CM Input Circuit VIC is the desire input common-mode voltage, VCM = CM, and RIN = RG + RS||RT. To set to mid-supply, To facilitate testing with common lab equipment, the make the value of RPU = RG+ RS||RT. THS4509 EVM allows split-supply operation, and the characterization data presented in this data sheet Table 3 is a modification of Table 1 to add the proper was taken with split-supply power inputs. The device values with RPU assuming a 50 Ω source impedance can easily be used with a single-supply power input and setting the input and output common-mode without degrading the performance. Figure 84, voltage to mid-supply. Figure 85, and Figure 86 show dc and ac-coupled There are two drawbacks to this configuration. One is single-supply circuits with single-ended inputs. These it requires additional current from the power supply. configurations all allow the input and output Using the values shown for a gain of 10 dB requires common-mode voltage to be set to mid-supply 37 mA more current with 5-V supply, and 22 mA allowing for optimum performance. The information more current with 3-V supply. presented here can also be applied to differential input sources. The other drawback is this configuration also increases the noise gain of the circuit. In the 10-dB In Figure 84, the source is referenced to the same gain case, noise gain increases by a factor of 1.5. voltage as the CM pin (VCM). VCM is set by the internal circuit to mid-supply. RT along with the input Table 3. RPU Values for Various Gains impedance of the amplifier circuit provides input termination, which is also referenced to VCM. Gain RF RG RIT RPU 6 dB 348 Ω 169 Ω 64.9 Ω 200 Ω Note RS and RT are added to the alternate input from the signal input to balance the amplifier. Alternately, 10 dB 348 Ω 102 Ω 78.7 Ω 133 Ω one resistor can be used equal to the combined value 14 dB 348 Ω 61.9 Ω 115 Ω 97.6 Ω RG+ RS||RT on this input. This is also true of the 20 dB 348 Ω 40.2 Ω 221 Ω 80.6 Ω circuits shown in Figure 85 and Figure 86. Copyright © 2008, Texas Instruments Incorporated Submit Documentation Feedback 27 Product Folder Link(s): THS4509-Q1 |
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