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DRV401 Datasheet(PDF) 17 Page - Burr-Brown (TI) |
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DRV401 Datasheet(HTML) 17 Page - Burr-Brown (TI) |
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17 / 28 page  DRV401 SBVS070A − JUNE 2006 − REVISED OCTOBER 2006 www.ti.com 17 SHUNT SENSE AMPLIFIER The differential (H-bridge) driver arrangement for the compensation coil requires a differential sense amplifier for the shunt voltage. This differential amplifier offers wide bandwidth and a high slew rate for fast current sensors. Excellent dc stability and accuracy result from an auto-zero technique. The voltage gain is 4V/V, set by precisely matched and stable internal SiCr resistors. Both inputs of the differential amplifier are normally connected to the current shunt resistor. This resistor adds to the internal (10k Ω) resistor, slightly reducing the gain in this leg. For best common-mode rejection (CMR), a dummy shunt resistor (R5) is placed in series with the REFIN pin to restore matching of both resistor dividers, as shown in Figure 5a. For gains of 4V/V: 4 + R 2 R 1 + R 4 ) R 5 R SHUNT ) R 3 With R2/R1 = R4/R3 = 4; R5 = RSHUNT × 4 Typically, the gain error resulting from the resistance of RSHUNT is negligible; for 70dB of common-mode rejection, however, the match of both divider ratios needs to be better than 1/3000. The amplifier output can drive close to the supply rails, and is designed to drive the input of a SAR-type ADC; adding an RC low-pass filter stage between the DRV401 and the ADC is recommended. This filter not only limits the signal bandwidth but also decouples the high-frequency component of the converter input sampling noise from the amplifier output. For RF and CF values, refer to the specific converter recommendations in the specific product data sheet. Empirical evaluation may be necessary to obtain optimum results. The output can drive 100pF directly and shows 50% overshoot with approximately 1nF capacitance. Adding RF allows much larger capacitive loads, as shown in Figure 5b and Figure 5c. Note that with RF of only 20 Ω, the load capacitor should be either smaller than 1nF or larger than 33nF to avoid overshoot; with RF of 50 Ω this transient area is avoided. a) Internal difference amplifier with an example of a decoupling filter. 10 µs/div b) VOUT of Figure 5a with R5 = 20Ω and CD = 100nF. 10 µs/div c) VOUT of Figure 5a with R5 = 50Ω and CD = 10nF. R 2 40k Ω R 1 10k Ω R 4 40k Ω R 3 10k Ω R 5 Dummy Shunt Differential Amplifier R F 50 Ω Decoupling, Low−Pass Filter REF IN Compensated REF IN ADC V OUT C F 10nF R SHUNT I COMP2 K2 DRV401 Differential Amplifier Section NOTE: R 5 is a dummy shunt resistor equal to 4x RSHUNT to compensate for RSHUNT and provide best CMR. Figure 5. Internal Difference Amplifier with Example of a Decoupling Filter (2) |
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Descripción similar - DRV401 |
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