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TS1109-200IDT833 Datasheet(PDF) 4 Page - Silicon Laboratories |
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TS1109-200IDT833 Datasheet(HTML) 4 Page - Silicon Laboratories |
4 / 20 page 2.2 Current Sense Amplifier + Output Buffer The internal configuration of the TS1109 bidirectional current-sense amplifier is a variation of the TS1101 bidirectional current-sense amplifier. The TS1109 current-sense amplifier is configured for fully differential input/output operation. Referring to the block diagram, the inputs of the TS1109’s differential input/output amplifier are connected to RS+ and RS– across an external RSENSE resistor that is used to measure current. At the non-inverting input of the current-sense amplifier, the applied voltage difference in voltage between RS+ and RS– is ILOAD x RSENSE. Since the RS– terminal is the non-inverting input of the internal op-amp, the current-sense op-amp action drives PMOS[1/2] to drive current across RGAIN[A/B] to equalize voltage at its inputs. Thus, since the M1 PMOS source is connected to the inverting input of the internal op-amp and since the voltage drop across RGAINA is the same as the external VSENSE, the M1 PMOS’ drain-source current is equal to: IDS(M 1) = VSENSE RGAINA IDS(M 1) = ILOAD × RSENSE RGAINA The drain terminal of the M1 PMOS is connected to the transimpedance amplifier’s gain resistor, ROUT, via the inverting terminal. The non-inverting terminal of the transimpedance amplifier is internally connected to VBIAS, therefore the output voltage of the TS1109 at the OUT terminal is: VOUT = VBIAS − ILOAD × RSENSE × ROUT RGAINA When the voltage at the RS– terminal is greater than the voltage at the RS+ terminal, the external VSENSE voltage drop is impressed upon RGAINB. The voltage drop across RGAINB is then converted into a current by the M2 PMOS. The M2 PMOS drain-source current is the input current for the NMOS current mirror which is matched with a 1-to-1 ratio. The transimpedance amplifier sources the M2 PMOS drain-source current for the NMOS current mirror. Therefore, the output voltage of the TS1109 at the OUT terminal is: VOUT = VBIAS + ILOAD × RSENSE × ROUT RGAINB When M1 is conducting current (VRS+ > VRS–), the TS1109’s internal amplifier holds M2 OFF. When M2 is conducting current (VRS– > VRS+), the internal amplifier holds M1 OFF. In either case, the disabled PMOS does not contribute to the resultant output voltage. The current-sense amplifier’s gain accuracy is therefore the ratio match of ROUT to RGAIN[A/B]. For each of the two gain options availa- ble, The following table lists the values for RGAIN[A/B]. Table 2.1. Internal Gain Setting Resistors (Typical Values) GAIN (V/V) RGAIN[A/B] (Ω) ROUT (Ω) Part Number 20 2 k 40 k TS1109-20 200 200 40 k TS1109-200 The TS1109 allows access to the inverting terminal of the transimpedance amplifier by the FILT pin, whereby a series RC filter may be connected to reduce noise at the OUT terminal. The recommended RC filter is 4 kΩ and 0.47 µF connected in series from FILT to GND to suppress the noise. Any capacitance at the OUT terminal should be minimized for stable operation of the buffer. TS1109 Data Sheet System Overview silabs.com | Smart. Connected. Energy-friendly. Rev. 1.0 | 3 |
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