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ADR370 Folha de dados(PDF) 7 Page - Analog Devices |
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ADR370 Folha de dados(HTML) 7 Page - Analog Devices |
7 / 12 page REV. A ADR370 –7– APPLICATIONS Low Cost Negative Reference A low cost negative reference can be obtained by leveraging the current sinking capability of the ADR370. Simply tying the VOUT terminal to ground and adding a bias resistor, RSET, to the GND pin of the device, a negative voltage reference can be obtained as shown in Figure 3. RSET should be chosen such that ISET remains between 1 mA to 5 mA. VIN VDD VSS RSET ISET ADR370 VOUT GND –VREF Figure 3. Low Cost Negative Reference Precision Negative Reference Without using any matching resistors, a precision negative reference can be obtained using the configuration shown in Figure 4. The voltage difference between VOUT and GND of the ADR370 is 2.048 V. Since VOUT is at virtual ground, U2 will close the loop by forcing the GND pin to be the negative reference node. U2 should be a low offset voltage precision op amp, such as the OP1177. VIN +15V U2 U1 2.3V TO 12V OP1177 –15V ADR370 VOUT GND –VREF Figure 4. Precision Negative Reference Low Cost Current Source Figure 5 illustrates how a simple, low cost current source can be configured using the ADR370. The load current, IL, is simply the sum of ISET and the quiescent current, Iq. ISET is simply the reference voltage generated by the ADR370 divided by RSET. I V R SET SET = 2 048 . (4) The quiescent current, Iq, varies slightly with load. The variation in Iq limits the use of this circuit to general-purpose applications. VIN VL + 2.5V < VDD < VL + 12V ADR370 VOUT GND ISET = RSET RSET VL RL IL Iq = 65 A 2.048V Figure 5. Low Cost Current Source Precision Current Source with Adjustable Output A precision current source can be implemented with the circuit shown in Figure 6. By adding a mechanical or digital potenti- ometer, this circuit becomes an adjustable current source. If a digital potentiometer like the AD5201 is used, the load current is simply the voltage across terminals B-to-W of the digital potentiometer divided by RSET. I VD R L REF SET = × × 256 (5) where D is the decimal equivalent of the digital potentiometer input code. VIN +12V A B W –2.048V TO VL 0V TO (2.048V + VL) 12V OP1177 AD5201 –12V ADR370 VOUT GND VL RL RSET IL Figure 6. Programmable 0 mA to 5 mA Current Source To optimize the resolution of this circuit, dual supply op amps should be used because the ground potential of ADR370 can swing from –2.048 V at zero scale to VL at full scale of the potentiometer setting. |
Nº de peça semelhante - ADR370 |
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Descrição semelhante - ADR370 |
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