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resources:eval:developer-kits:pulser-plus:theoryofoperation [29 Jan 2024 17:19] – [PA Drain Current Sense] Luc Perreaultresources:eval:developer-kits:pulser-plus:theoryofoperation [29 Jan 2024 18:11] (current) – [PA Drain Current Sense] Eamon Nash
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 {{\drain_pulser_circuit.png?direct&1200 |Drain pulser circuit}} {{\drain_pulser_circuit.png?direct&1200 |Drain pulser circuit}}
  
-The drain pulse generator comprises of the [[adi>LTC7000A]], FET and the crowbar circuit ([[adi>ADP3625]] + FET). To pulse the drain, apply a 0-3.3V pulse onto the //<fc #008080>DRAIN_PULSE_ENABLE</fc>// SMA connector. The pulse modulates the INP pin of the [[adi>LTC7000A]] which, in turn, drives Q1 on and off. A high on //<fc #008080>DRAIN_PULSE_ENABLE</fc>// turns on the FET and applies //<fc #008080>VDD</fc>// onto the PA drain. +The drain pulse generator comprises of the [[adi>LTC7000A]], FET and the crowbar circuit ([[adi>ADP3625]] + FET). To pulse the drain, apply a 0-3.3V pulse onto the //<fc #008080>DRAIN_PULSE_ENABLE</fc>// SMA connector. The pulse modulates the INP pin of the [[adi>LTC7000A]] which, in turn, drives Q1 on and off. A high on //<fc #008080>DRAIN_PULSE_ENABLE</fc>// turns on the FET and applies //<fc #008080>VDD</fc>// onto the PA drain. 
  
 The turn-on time is controlled by the [[adi>LTC7000A]].TGUP signal and the amount of capacitance connected to the PA drain (//<fc #008080>VDD_PA</fc>// signal). Too much capacitance on the PA drain rail can not only slow down the turn-on edges but also create large input current spikes on the line. To avoid such issues, it is recommended to keep the total amount of capacitance at the PA drain to less than 10nF.  The turn-on time is controlled by the [[adi>LTC7000A]].TGUP signal and the amount of capacitance connected to the PA drain (//<fc #008080>VDD_PA</fc>// signal). Too much capacitance on the PA drain rail can not only slow down the turn-on edges but also create large input current spikes on the line. To avoid such issues, it is recommended to keep the total amount of capacitance at the PA drain to less than 10nF. 
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 {{\drain_pulser_circuit.png?linkonly|"Drain pulser circuit"}} ). {{\drain_pulser_circuit.png?linkonly|"Drain pulser circuit"}} ).
 To measure, the test equipment connected can be terminated to either 50Ω or high-Z with limitations for each.  To measure, the test equipment connected can be terminated to either 50Ω or high-Z with limitations for each. 
-  * 50Ω terminated: <fc #ff0000>50Ω termination must not be used when the drain pulser is set to stay on for relatively long periods of time</fc> (ex. Gate pulsing). It’ll damage resistor R28 and the PCB. To use when drain pulsing with pulse width <300μs per recommended operating conditions.\\ The conversion factor when 50Ω terminated is:+  * 50Ω terminated: <fc #ff0000>50Ω termination must not be used when the drain pulser is set to stay on for relatively long periods of time</fc> (ex. Gate pulsing). It will damage resistor R28 and the PCB. To use when drain pulsing with pulse width <300μs per recommended operating conditions.\\ The conversion factor when 50Ω terminated is:
  
-<WRAP centeralign> V<sub>//@<fc #008080>VDD_PA_SNS</fc>//</sub> = V<sub>//@<fc #008080>VDD_PA</fc>//</sub> × R<sub>TERMINATION</sub> / (R<sub>TERMINATION</sub> + R28) +<WRAP centeralign> V<sub>//<fc #008080>VDD_PA_SNS</fc>//</sub> = V<sub>//<fc #008080>VDD_PA</fc>//</sub> × R<sub>TERMINATION</sub> / (R<sub>TERMINATION</sub> + R28) 
  
-V<sub>//@<fc #008080>VDD_PA_SNS</fc>//</sub> = V<sub>//@<fc #008080>VDD_PA</fc>//</sub> × 47.6mV/V </WRAP>+V<sub>//<fc #008080>VDD_PA_SNS</fc>//</sub> = V<sub>//<fc #008080>VDD_PA</fc>//</sub> × 47.6mV/V </WRAP>
  
   * High-Z termination: Careful with added capacitance that form an R-C filter with R28. It may affect measurement accuracy.   * High-Z termination: Careful with added capacitance that form an R-C filter with R28. It may affect measurement accuracy.
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 There are two means of measuring the PA drain current on this evaluation board.  There are two means of measuring the PA drain current on this evaluation board. 
-  - Via the [[adi>LTC7000A]].IMON pin. It has the advantage of not requiring any additional circuitry for monitoring the current. However, its response time can be significantly slower and is limited to pulses with on-times greater than 20-30μs. The [[adi>LTC7000A]].IMON response can be faster than the 20-30us depending on the operating conditions. \\ The [[adi>LTC7000A]].IMON voltage can be measured differentially across the //<fc #008080>IMONP</fc>// and //<fc #008080>IMONN</fc>// terminals with a high-impedance probe. To estimate the drain current from //<fc #008080>IMONP/N</fc>// terminals: \\ \\ <WRAP centeralign> V<sub>//<fc #008080>@IMONP</fc>//</sub> − V<sub>//<fc #008080>@IMONN</fc>//</sub> = (I<sub>DRAIN</sub> × 10mΩ × 200μA/V) × (100kΩ ⁄⁄ R56) \\  I<sub>DRAIN</sub> = (V<sub>//<fc #008080>@IMONP</fc>//</sub> − V<sub>//<fc #008080>@IMONN</fc>//</sub>) × 33A/V </WRAP> Removing the 20kΩ resistor connected to [[adi>LTC7000A]].IMON pin, R56, allows a larger signal to be measured across //<fc #008080>IMONP/N</fc>// at the expense of a slower response. The [[adi>LTC7000A]].IMON pin has 100kΩ of ROUT.\\  +  - Via the [[adi>LTC7000A]].IMON pin. It has the advantage of not requiring any additional circuitry for monitoring the current. However, its response time can be significantly slower and is limited to pulses with on-times greater than 20-30μs. The [[adi>LTC7000A]].IMON response can be faster than the 20-30us depending on the operating conditions. \\ The [[adi>LTC7000A]].IMON voltage can be measured differentially across the //<fc #008080>IMONP</fc>// and //<fc #008080>IMONN</fc>// terminals with a high-impedance probe. To estimate the drain current from //<fc #008080>IMONP/N</fc>// terminals: \\ \\ <WRAP centeralign> V<sub>//<fc #008080>IMONP</fc>//</sub> − V<sub>//<fc #008080>IMONN</fc>//</sub> = (I<sub>DRAIN</sub> × 10mΩ × 200μA/V) × (100kΩ ⁄⁄ R56) \\  I<sub>DRAIN</sub> = (V<sub>//<fc #008080>IMONP</fc>//</sub> − V<sub>//<fc #008080>IMONN</fc>//</sub>) × 33A/V </WRAP> Removing the 20kΩ resistor connected to [[adi>LTC7000A]].IMON pin, R56, allows a larger signal to be measured across //<fc #008080>IMONP/N</fc>// at the expense of a slower response. The [[adi>LTC7000A]].IMON pin has 100kΩ of ROUT.\\  
-  - Using the [[adi>LT1999|LT1999-10]] current sense amplifier. It provides significantly faster response (<1μs) than the [[adi>LTC7000A]].IMON circuit but requires an additional IC. It can measure drain currents pulses down to the recommended 10μs on-time minimum. \\ The measurement is done differentially across the //<fc #008080>ISNSP</fc>// and //<fc #008080>ISNSN</fc>// terminals using a high-impedance probe. Don’t try using a single-ended probe with ground terminal attached to //<fc #008080>ISNSN</fc>//, //<fc #008080>ISNSN</fc>// is NOT grounded. To convert:\\ \\ <WRAP centeralign> V<sub>//<fc #008080>@ISNSP</fc>//</sub> − V<sub>//<fc #008080>@ISNSN</fc>//</sub> = I<sub>DRAIN</sub> × 10mΩ × 10V/V \\ I<sub>DRAIN</sub> = (V<sub>//<fc #008080>@ISNSP</fc>//</sub> − V<sub>//<fc #008080>@ISNSN</fc>//</sub>) × 10A/V </WRAP>  For more signal at the //<fc #008080>ISNSP/N</fc>// terminals, the gain of the LT1999 can be increased by selecting either the [[adi>LT1999|LT1999-20]], gain of 20, or [[adi>LT1999|LT1999-50]]), gain of 50. The gain increase comes at the expense of a slower response time.+  - Using the [[adi>LT1999|LT1999-10]] current sense amplifier. It provides significantly faster response (<1μs) than the [[adi>LTC7000A]].IMON circuit but requires an additional IC. It can measure drain currents pulses down to the recommended 10μs on-time minimum. \\ The measurement is done differentially across the //<fc #008080>ISNSP</fc>// and //<fc #008080>ISNSN</fc>// terminals using a high-impedance probe. Don’t try using a single-ended probe with ground terminal attached to //<fc #008080>ISNSN</fc>//, //<fc #008080>ISNSN</fc>// is NOT grounded. To convert:\\ \\ <WRAP centeralign> V<sub>//<fc #008080>ISNSP</fc>//</sub> − V<sub>//<fc #008080>ISNSN</fc>//</sub> = I<sub>DRAIN</sub> × 10mΩ × 10V/V \\ I<sub>DRAIN</sub> = (V<sub>//<fc #008080>ISNSP</fc>//</sub> − V<sub>//<fc #008080>ISNSN</fc>//</sub>) × 10A/V </WRAP>  For more signal at the //<fc #008080>ISNSP/N</fc>// terminals, the gain of the LT1999 can be increased by selecting either the [[adi>LT1999|LT1999-20]], gain of 20, or [[adi>LT1999|LT1999-50]]), gain of 50. The gain increase comes at the expense of a slower response time.
  
 To improve measurement accuracy, it is preferable to calibrate the current monitoring path. One approach would be to connect an electronic load on //<fc #008080>VDD_PA</fc>// and setting the //<fc #008080>DRAIN_PULSE_ENABLE</fc>// voltage to 3.3V to turn-on the <fc #008080>//VDD//</fc> drain path.  To improve measurement accuracy, it is preferable to calibrate the current monitoring path. One approach would be to connect an electronic load on //<fc #008080>VDD_PA</fc>// and setting the //<fc #008080>DRAIN_PULSE_ENABLE</fc>// voltage to 3.3V to turn-on the <fc #008080>//VDD//</fc> drain path. 
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 Amplifier A1a, [[adi>ADA4896-2]], is used as a buffer/level-shifter amplifier for the pinch-off threshold reference voltage. To set the pinch-off voltage, adjust R42 and R43 per equation:  Amplifier A1a, [[adi>ADA4896-2]], is used as a buffer/level-shifter amplifier for the pinch-off threshold reference voltage. To set the pinch-off voltage, adjust R42 and R43 per equation: 
  
-<WRAP centeralign> V<sub>PINCH_OFF</sub> = V<sub>//<fc #008080>@LT3093_VEE</fc>//</sub> * R42 / (R42 + R43) </WRAP>+<WRAP centeralign> V<sub>PINCH_OFF</sub> = V<sub>//<fc #008080>LT3093_VEE</fc>//</sub> * R42 / (R42 + R43) </WRAP>
  
 The eval is set to -5.0V V<sub>PINCH_OFF</sub>. The eval is set to -5.0V V<sub>PINCH_OFF</sub>.
resources/eval/developer-kits/pulser-plus/theoryofoperation.txt · Last modified: 29 Jan 2024 18:11 by Eamon Nash