APPLICATION NOTE | AN:035 Achieving High Accuracy Voltage (or Current) Regulation with the DCM Up to ± 1% regulation Xiaoyan Yu Applications Engineering August 2015 ContentsPage Introduction Loop Compensation The DC-DC Converter Module (DCM) provides isolation, regulation, fault protection and monitoring in a single module. Through a negative slope load line and temperature coefficient, DCM arrays implement wireless current sharing. In either single DCM circuits 2 or in arrays, the nominal load regulation is about 5% (see the %V OUT-LOAD specification in the DCM data sheet), excluding other regulation error terms. This may not be sufficient 3 for applications that have tight voltage regulation requirements. In those applications, an isolated analog feedback loop, such as the one shown in Figure 1, can be used to improve the load regulation performance. The circuit shown here is recommended for general use in high 5 accuracy applications that need to preserve the input-output isolation offered by the DCM. The circuit is applicable to single DCMs as well as arrays of up to eight units. 6 Experimental Results 8 Introduction1 Circuit Schematic Functional Description Remote Sense Circuit Component Selection Conclusion10 Appendix I 11 Appendix II 12 For array applications, on the primary side, after any needed differential-mode filtering, the DCMs must share a common –IN node, which is also the ground reference for the remote sense sub circuit output. The DCM TR pins are all driven by single output of the remote sense sub circuit, so it is important to minimize voltage differences between the various DCM –IN pins through careful layout techniques. On the secondary side, the remote sense sub circuit senses the output voltage through the R1/R2 resistor network, compares that to a reference voltage, and converts the error voltage into a trim voltage for the whole array. Since the DCMs are all effectively programmed to the same trim voltage, the current sharing between modules is still the same as it would be without the remote sense circuit, as covered in AN030: Parallel DCMs. This circuit works with all ChiP DCM types, and achieves a regulation accuracy of ±1% at all line, load, temperature, and trim conditions. AN:035 vicorpower.com Applications Engineering: 800 927.9474 Page 1 Circuit Schematic Figure 1. Remote Sense Circuit for DCM Module 1 RTRIM_1 TR EN FT +IN +IN +OUT +OUT -IN -IN -OUT -OUT RTRIM_2 Module 2 TR EN FT ≈≈ +IN +OUT -IN -OUT ≈≈ ≈ Module N RTRIM_N TR EN FT +IN +OUT -IN -OUT PRI-GND EMI-GND SEC-GND VOUT VTR U3 CNY17-3 5 C5 1nF 5VFILT L1 LQH32CN330 1 R7 VEAO 1 2 4 R6 400Ω PRI-SGND 5 U2 2 MAX4238 U1 ADR361 VREF 6 2.5V 3 4 C1 4 VO VIN 3 GND 2 R8 1kΩ 1 U4 LM2936HVMAX-5.0* 8 VO VIN 7 GND C9 6 GND 0.1uF C6/C7/C8 C2012X6S1H475 R3 R1 2.2uF (120 kΩ/N) – (R1||R2) ECW-FD2W225J Remote sense circuit C2 10uF 5V SEC-SGND (VOUT-2.5)*R1/2.5 R2 10kΩ *See Table 1 AN:035 vicorpower.com Applications Engineering: 800 927.9474 Page 2 Functional Description of Remote Sense Circuit The output voltage is sensed through resistor network R1 and R2 relative to secondary ground SEC-SGND; the sensed voltage becomes R2 VOUT • (1) R1 + R2 1. The sensed voltage is compared to the reference voltage VREF, which in this schematic is generated by the 2.5 V reference U1. VREF = 2.5 V (2) If another VREF voltage is preferred, VREF is recommended to be between 1.5 V and 3 V for optimum noise immunity. 2. The difference gets accumulated by an integrating error amplifier (consisting of R3, C1 and U2), which generates VEAO. 3. The difference between VEAO and 5 VFILT drives the input of the optocoupler U3. 4. The optocoupler (U3) is used to preserve the galvanic isolation of the DCM array. 5. The output of U3 is its collector current. That current develops a voltage drop across the RTRIM_x and RTRIM-INT_x resistors and establishes the DCM trim pin voltages. (The RTRIM-INT_x are the internal pull-up resistors inside each DCM. Each RTRIM-INT_x pulls up to VCC, the DCM’s internally generated 3.3 V supply.) Figure 2 details how the trim pin voltages are generated, along with a simplified model for N DCMs in parallel. The RTRIM_x resistors are all the same nominal value, as are all of the RTRIM-INT_x resistors. Figure 2. Trim Voltage Generation Method and It's Simplified Model DCM1 RTRIM-INT_1 RTRIM_1 3.3V VTR’_1 DCM2 RTRIM-INT_2 RTRIM_2 VTR’_2 3.3V 3.3V VTR’_N U3 VTR VTR VTR 5VFILT 5 1 4 2 C5 R7 PRI-SGND RTRIM-INT_x / N VTR’ DCMN RTRIM-INT_N RTRIM_N C5 RTRIM_x/N 3.3V Optocoupler R6 U3 VTR 5VFILT 1 4 2 R7 Optocoupler R6 VEAO VEAO 6. VTR 5 If the sensed version of VOUT is less than VREF, the error amplifier output rises, and the drive current into the optocoupler’s LED is reduced. This in turn reduces the optocoupler’s (output) collector current, permitting the pull-up resistors to pull the trim voltage higher, which raises each DCMs programmed output trim voltage. Conversely, if VOUT is too high, the DCM trim pin voltages are similarly driven lower, which lowers VOUT. AN:035 vicorpower.com Applications Engineering: 800 927.9474 Page 3 7. R6 is chosen to set the voltage transfer ratio of the optocoupler, to ensure that it operates as expected over temperature and with age (see Appendix I). 8. R7 establishes a minimum load on the TR pins by setting the maximum trim bus voltage. a. R7 must be chosen so that the maximum trim voltage will be below the TR trim enable threshold, even with no optocoupler current; some margin is needed so that trim remains enabled in the presence of noise. b. The value of R7 may be further reduced, to limit the maximum trim voltage, which can be helpful in reducing overshoot during load transients and startup. For N DCMs in parallel, the trim voltage input to the DCM, VTR’_x (see Figure 2), can be calculated as: VTR’max = 3.3 • N • R7 + RTRIM_x N • R7 + RTRIM_x + RTRIM-INT_x (3) Where RTRIM_x = 301 Ω, RTRIM-INT_x = 10 kΩ as specified in the DCM datasheet, N is the number of DCMs in parallel. Thus the maximum trim voltage input can be calculated as: VTR’max = 3.3 • N • R7 + 10301 (4) For example, if the trim voltage is to be limited to 3 V, the value of R7 can be chosen as: R7 = N • R7 + 301 100 kΩ N (5) C5 is a low value ceramic capacitor, such as 1 nF, which is used to exclude high frequency noise from VTR. 9. The bus that is used to supply U1, U2 and U3 is generated from VOUT. Through this method, no external 5 V power supply is needed. U4 regulates VOUT to an unfiltered 5 V, which is called 5 V in Figure 1. This 5 V then goes through the filter network (C2, L1, C6-C8) and becomes a filtered 5 V, which is called 5 VFILT. R8 discharges the filter capacitors when VOUT is off. The output of this circuit is the 5 VFILT bus that supplies U1, U2 and U3. 10. Optionally, U4/C6-C8/L1/C2/R8 can be removed from the circuit if a precision external 5 V power supply with at least 50 mA capability is available to drive the 5 VFILT bus. The benefit of using an external 5 V power supply is that it uses fewer components. The disadvantage is that if the external supply is energized before the DCMs are enabled, then the error amplifier will “wind up” to a maximum trim condition. When the DCM are started, the system output voltage will significantly overshoot the setpoint until the integrator unwinds. When using an external 5 V power supply, R7 should be chosen carefully so that VOUT does not exceed the maximum voltage allowed by the application, or the DCMs should be enabled prior to energizing the external 5 V supply node. AN:035 vicorpower.com Applications Engineering: 800 927.9474 Page 4 Through this method, the output voltage of the DCM can be trimmed to: VOUT = VREF • R1 + R2 (6) R2 The maximum cut off frequency of the whole loop is 30 Hz, but with CTR variance, temperature, and aging of the optocoupler, it can be as low as approximately 7.5 Hz. Table 1. VOUT Notes for the Choice of U4 U4 Recommendation 6 V ≤ VOUT ≤ 60 V Use LM2936HVMAX-5.0 for U4 VOUT ≤ 6 V Use an appropriate regulator for U4 so that the output voltage of U4 will be between 4 V and 5.5 V, or use an independent supply rail in the application Comment For DCM modules with a rated VOUT-NOM of 5 V or 3.3 V, for example. Component Selection The following resources can be used to facilitate the selection of filter network components: n Each DCM’s datasheet n AN030: Parallel DCMs (www.vicorpower.com/documents/application_notes/an_Parallel_DCMs.pdf) n Powerbench Filter Design Tool (app2.vicorpower.com/filterDesign/intiFilter.do) n AN023: Filter Network Design for DC-DC Converter Modules (www.vicorpower.com/documents/application_notes/vichip_appnote23.pdf) The detailed schematic of the DCM remote sense circuit has been shown in Figure 1, with IC device types and component values. The generic components’ part numbers have not been marked in the schematic. Unconnected pins have not been shown for simplicity. AN:035 vicorpower.com Applications Engineering: 800 927.9474 Page 5 The recommended components for the remote sense circuit are summarized here (excluding the generic components): Table 2. Part ID Recommended Components for Remote Sense Circuit Type Manufacturer Part Number Digi-Key Part Number Note C1 CAP FILM 2.2 UF 450 VDC RADIAL ECW-FD2W225J PCF1609-ND Low leakage, low dielectric absorption U1 IC VREF SERIES 2.5 V TSOT23-5 ADR361BUJZ-REEL7 ADR361BUJZREEL7CT-ND High precision U2 IC OPAMP GP 1 MHZ RRO SOT23-6 MAX4238AUT+T MAX4238AUT+ TDKR-ND Low input offset voltage, low input offset current, low supply consumption, but not necessarily high bandwidth or high slew rate U3 OPTOISO 5 KV TRANS W/BASE 6SMD CNY17-3X017T CNY173X017TCT-ND 5 kV isolation; Current Transfer Ratio no less than 100% @ 10 mA U4 IC REG LDO 5 V 50 MA 8SOIC LM2936HVMAX-5.0/NOPB LM2936HVMAX-5.0/ NOPBCT-ND See Table 1 C6/C7/C8 CAP CER 4.7 UF 50 V 20% X6S 0805 C2012X6S1H475M125AC 445-7600-1-ND L1 IC VREF SERIES 2.5 V TSOT23-5 ADR361BUJZ-REEL7 ADR361BUJZREEL7CT-ND High precision R1, R2 and R7 may vary according to the application and DCM module. Consider the following before choosing these values: a. R1/R2 = VOUT/VREF -1, VOUT is the trimmed DCM output voltage. b. Choose high accuracy resistors (up to 0.1% accuracy) for R1 and R2; their accuracy directly relates to the resultant output voltage setpoint. VOUT-2.5 • R2 c. Choose R2 = 10 kΩ; then the resistance of R1 can be calculated as: R1 = 2.5 This will minimize current consumption and power dissipation in the divider network, while maintaining good immunity from noise and effects of bias currents from amplifier input. With R2 being fixed at 10 kΩ, a high accuracy resistor value for R1 may not be available. In that case, the nominal value of R2 can be adjusted to be within +/-10% of 10 kΩ. d. R7 limits the maximum programmed trim for the DCMs. Use Equation (3) to determine the value of R7. Loop Compensation When trim is active, the DCM TR pin provides dynamic trim control of the module’s output voltage with at least 30 Hz of (small signal) control bandwidth over the output voltage of the DCM converter. The phase shift at 30 Hz is approximately 45°. AN:035 vicorpower.com Applications Engineering: 800 927.9474 Page 6 The whole open loop transfer function at 30 Hz or below can be calculated as: A (s) = ATR (s) • R2 • R2 + R1 1 R3’ • C1 • s • CTR • RTRIM-INT_x N • R6 (7) Where CTR is the Current Transfer Ratio of the optocoupler, which is specified in the optocoupler data sheet; R3’ = R3 + R1 • R2 ; recall that N is the number of DCM modules in parallel. R1 + R2 For frequencies less than or equal to 30 Hz, the analysis is as follows: ATR (s) is the transfer function from TR to VOUT, which is a constant ATR at very low frequency and ≤ ATR at 30 Hz. VOUT • R2 R1 + R2 = 2.5 (8) Rearranging the equality: R2 = R2 + R1 2.5 (9) VOUT Multiplying both sides by ATR (s), ATR (s) • R2 = R2 + R1 2.5 • ATR (s) (10) VOUT 2.5 • ATR (s) The term VOUT increases with increasing trim range. For existing DCMs, the widest trim range is −40% to 10% of VOUT_NOM. For these DCMs, 2.5 • ATR VOUT_MIN ≈1 Therefore: ATR (s) • R2 ≤1 R2 + R1 (11) Inserting this result into Equation (7): A(s) ≤ 1 • 1 R3’ • 2.2 µF • s • CTR • 10 kΩ N • 400 (12) If R3 is chosen so that A(s) goes to 0 dB at 30 Hz, the whole system will have approximately 45° phase margin. AN:035 vicorpower.com Applications Engineering: 800 927.9474 Page 7 Setting A(s) to 0 dB at 30 Hz results in: 60 kΩ • CTR R3’ = (13) N For the optocoupler used in the schematic, the maximum CTR is in the range of 1 to 2. So for the worst case gain, CTR = 2: R3’ = R3 = 120 kΩ (14) N 120 kΩ N – R1 • R2 (15) R1 + R2 Experimental Results (Steady State, Startup, and Transient) Steady State Load Regulation Using the DCM300P480T500A40 as an example, experimental results for a single DCM are shown in Figure 3; the results for an array of eight DCMs are shown in Figure 4. Figure 3. The Experimental Results for Single DCM300P480T500A40 with this Remote Sense Circuit Low Trim High Trim 0.25 VOUT Regulation Error (%) VOUT Regulation Error (%) 0.25 0.15 0.05 -0.05 -0.15 0.15 0.05 -0.05 -0.15 -0.25 -0.25 0 20 40 60 80 0 100 20 Low Line 40 60 80 100 80 100 Rated Load (%) Rated Load (%) Low Line Nom Line Nom Line High Line High Line Figure 4. Experimental Results for an 8-up DCM300P480T500A40 Array with this Remote Sense Circuit Low Trim 0.15 0.05 -0.05 -0.15 -0.25 0.15 0.05 -0.05 -0.15 -0.25 0 20 40 60 80 Rated Load (%) Low Line Nom Line High Line High Trim 0.25 VOUT Regulation Error (%) VOUT Regulation Error (%) 0.25 AN:035 vicorpower.com 100 0 20 40 60 Rated Load (%) Low Line Nom Line High Line Applications Engineering: 800 927.9474 Page 8 Startup Typical startup waveforms are shown in Figure 5 and Figure 6. During startup, once VOUT reaches U4’s minimum input voltage, U4 will generate the 5 V bus to supply U1, U2 and U3. The waveform of the startup typically comes in two stages: in the first stage, VOUT rises to the minimum trimmed VOUT; in the second stage, the circuit comes to the steady state and brings VOUT to the correct trimmed value. This circuit needs to be started up after VOUT and the 5 V bus have fully discharged to avoid trimming to the highest VOUT. Figure 5. Experimental Results for a Single DCM300P480T500A40 (low line, maximum external COUT) Startup into High Trim with this Remote Sense Circuit (a) 10% Load (b) Full Load (Electronics Load in CR Mode) (a) 10% Load (b) Full Load (Electronics Load in CR Mode) Figure 6. Experimental Results for a single DCM300P480T500A40 (high line, maximum external COUT) Startup into Low Trim with this Remote Sense Circuit Load Transient Response There is a delay from the transient until the circuit reaches the corrected output voltage, which is due to the limited bandwidth of the DCM TR pin and remote sense circuit. Because of this narrow bandwidth, the remote sense circuit doesn’t affect the initial response to a transient. Figure 7 shows a comparison of transient response without the remote sense circuit to the response with the remote sense circuit in operation. AN:035 vicorpower.com Applications Engineering: 800 927.9474 Page 9 Figure 7. Comparison of a Single DCM300P480T500A40 Transient Response (nominal line, nominal trim, electronic load in CC mode 10% to 100% load transient) without the Remote Sense Circuit and with the Circuit Included (a) Without Remote Sense Circuit (b) With Remote Sense Circuit Conclusion Using the remote sense circuit shown here, DCM-based voltage regulators can achieve output voltage accuracy of ±1%. Within the 30 Hz bandwidth of the circuit, other aspects of DCM operation are unchanged. This method works for any number of DCMs in parallel, up to eight. AN:035 vicorpower.com Applications Engineering: 800 927.9474 Page 10 Appendix I. Choosing R6 to Account for CTR Variance in the CNY17-3 Over Temperature and Time 1. Information from Vishay CNY17 datasheet (www.vishay.com/docs/83606/cny17.pdf): PARAMETER (Tamb = 25 °C, unless otherwise specified) TEST CONDITION PART CNY17-1 CNY17-2 CNY17-3 CNY17-4 CNY17-1 CNY17-2 CNY17-3 CNY17-4 VCE = 5 V, IF = 10 mA IC/IF 1.8 1.7 Tamb = 25 °C 1.6 Tamb = 0 °C 1.5 1.4 Tamb = - 25 °C 1.3 T = - 55 °C amb 1.2 1.1 Tamb = 50 °C 1.0 Tamb = 75 °C 0.9 Tamb = 100 °C 0.8 0.7 Tamb = 110 °C 0.6 0.1 1 10 100 IF - Forward Current (mA) 1.2 CTRNorm - Normalized CTR (NS) VF - Forward Voltage (V) VCE = 5 V, IF = 1 mA 1.0 0.8 0.6 MIN. 40 63 100 160 13 22 34 56 IF = 10 mA VCE = 5 V Tamb = 25 °C Tamb = 0 °C Tamb = - 40 °C Tamb = - 55 °C 0.4 Tamb = 50 °C Tamb = 75 °C Tamb = 100 °C 0.2 0 0.1 SYMBOL CTR CTR CTR CTR CTR CTR CTR CTR Tamb = 110 °C 1 10 100 IF - Forward Current (mA) Fig. 5 - Forward Voltage vs. Forward Current Fig. 11 - Normalized CTR (NS) vs. Forward Current TYP. MAX. 80 125 200 320 30 45 70 90 1.2 CTRNorm - Normalized CTR (sat) CURRENT TRANSFER RATIO 1.0 0.8 0.6 IF = 10 mA VCE = 0.4 V Tamb = 25 °C Tamb = 0 °C Tamb = - 40 °C Tamb = - 55 °C Tamb = 50 °C 0.4 0.2 0 0.1 UNIT % % % % % % % % Tamb = 75 °C Tamb = 100 °C Tamb = 110 °C 1 10 100 IF - Forward Current (mA) Fig. 12 - Normalized CTR (sat) vs. Forward Current Tables and Figures courtesy of Vishay Intertechnology, Inc. 2. Calculation of CNY17-3 controller current achievable over temperature and time: n Choosing R6 = 400 Ω, a supply voltage of 4 V (the lowest value specified in Table 1), CTR = 100% and estimating the voltage drop across the optocoupler at 1.28 V, the maximum forward current that the secondary side of the remote sense circuit could have over the full temperature range is approximately (4 V − 1.28 V)/400 Ω = 6.8 mA. n The next step is to find the minimum CTR at IF = 6.8 mA, using linear interpolation on the data in the table for IF = 1 mA and IF = 10 mA. This results in a minimum CTR of ((10 mA − 6.8 mA) · 34% + (6.8 mA − 1 mA) · 100%)/(10 mA – 1 mA) = 76.5% at 25⁰C n From the Normalized CTR curves above, CTR could decrease to 60% of its peak value n From Vishay reliability data, CTR is reduced by 15% over 8000 operation hours, operation with aging. n Since 3.3 V – (2.65 V · 1.25) = −0.01 V < 0 V, this will result in a trim voltage close to giving CTR = 45.9% · (1 − 15%) = 39% n Thus the collector current will be at least 6.8 mA · 39% = 2.65 mA, to ensure proper over temperature, which is 76.5% · 60% = 45.9% 0 V, which is sufficient to drive all DCMs to trim low. n When the forward current is small, the CNY17-3 will be able to drive all DCMs to high trim, so high trim is achievable for any choice of R6. Thus R6 = 400 Ω should be a valid choice for this circuit to work over temperature and time, from single DCMs through arrays of eight DCMs. AN:035 vicorpower.com Applications Engineering: 800 927.9474 Page 11 Appendix II. Current Regulation If current regulation is needed instead of voltage regulation, with some modifications, the remote sense circuit can be adapted to regulate a constant-current output. Instead of sensing the output voltage with R1 and R2, a shunt resistor is used to measure the output current. The voltage across the shunt resistor is sensed with an additional differential amplifier stage, which feeds R3. R1 and R2 are not present, since the current signal scaling is accomplished by current sense amplifier. The rest of the circuit is unchanged. A typical schematic with the current sense sub-circuit is shown in Figure 8. Notice that current regulation needs to be limited to the minimum rated output current (IOUT) of the DCM, to avoid interfering with the DCM’s operational current limit and cause issues. In applications such as battery charging, the actual VOUT can be different from the trimmed voltage of the DCM. Additional considerations may be needed: 1. The DCM has a minimum VOUT before it might detect output under voltage. For example, the DCM would not be able to charge a battery whose voltage is below VOUT_UVP. 2. The DCM current capability is reduced when the DCM is trimmed higher than nominal (regardless of the actual VOUT), so the output current from the system should be no higher than n · (Rated POUT/maximum VOUT-TRIMMING) to avoid entering current limit. The transfer function between the output current IOUT and the sense voltage VSENSE in Figure 8 is: VSENSE = IOUT • R8 • R9 • Gm (16) With an LMP8645HV, the typical Gm is 200 µA/V. Through this method, the total output current of the DCMs can be trimmed to: IOUT = VREF • 1 R8 • R9 • Gm AN:035 vicorpower.com (17) Applications Engineering: 800 927.9474 Page 12 Figure 8. Remote Sense Circuit for DCM for Current Regulation with Single Current Sense Shunt Module 1 RTRIM_1 TR EN FT +IN +IN +OUT IOUT R8 -IN -IN RTRIM_2 +OUT -OUT -OUT Module 2 U5 LMP8645HV 3 4 +IN -IN 2 5 VRG 1 6 VOUT V+ TR EN FT +IN +OUT -IN -OUT 5VFILT C10 0.1uF R9 VSENSE ≈≈ Current sense subcircuit ≈≈ ≈ Module N RTRIM_N TR EN FT +IN +OUT -IN -OUT PRI-GND EMI-GND SEC-GND VOUT VTR U3 CNY17-3 C5 1nF 5VFILT 5 1 4 2 R7 VEAO 1 R6 400Ω PRI-SGND 5 U2 2 MAX4238 L1 LQH32CN330 U1 ADR361 VREF 6 2.5V 3 4 4 VO VIN 3 GND 2 C2 10uF 2.2uF ECW-FD2W225J R8 1kΩ 1 U4 LM2936HVMAX-5.0* 8 VO VIN 7 GND C9 6 GND 0.1uF C6/C7/C8 C2012X6S1H475 R3 C1 5V SEC-SGND (120/N)kΩ Remote sense circuit *See Table 1 In high current applications, individual current sense resistors for each DCM output may be preferred (as shown in Figure 9) over using a single high-dissipation current sense resistor for the entire DCM array. With R81, R82, … R8N all equal to R8, and R91, R92, … R9N all equal to R9, the total output current of the DCMs can be trimmed to: IOUT = VREF • 1 R8 • R9 • Gm AN:035 vicorpower.com (18) Applications Engineering: 800 927.9474 Page 13 Figure 9. Remote Sense Circuit for DCM for Current Regulation with Individual Current Sense Shunts Module 1 RTRIM_1 TR EN Current sense subcircuit FT +IN +IN +OUT -IN -IN -OUT U51 LMP8645HV 3 4 +IN -IN 2 5 VRG 1 6 VOUT V+ Module 2 RTRIM_2 TR EN +IN +OUT -IN -OUT ≈ ≈≈ Module N RTRIM_N -OUT 5VFILT R91 C101 0.1uF FT VSENSE_1 R82 IOUT_2 U52 LMP8645HV 4 3 +IN -IN 5 2 VRG 6 1 VOUT V+ 5VFILT TR ≈≈ C102 0.1uF EN +OUT IOUT_1 R81 R92 VSENSE_2 FT +IN +OUT -IN -OUT PRI-GND EMI-GND R8N IOUT_N U5N LMP8645HV 4 3 +IN -IN 5 2 VRG 6 1 VOUT V+ 5VFILT SEC-GND C101 0.1uF R9N VSENSE_N VTR VOUT U3 CNY17-3 5 C5 1nF 5VFILT 1 R7 VEAO 1 2 4 R6 400Ω PRI-SGND 5 U2 2 MAX4238 VREF 6 2.5V 3 4 C1 2.2uF ECW-FD2W225J Remote sense circuit L1 LQH32CN330 U1 ADR361 VO VIN 3 4 GND 2 C2 10uF C6/C7/C8 C2012X6S1H475 U4 LM2936HVMAX-5.0* 1 VO VIN 8 7 GND C9 6 R8 GND 0.1uF 1kΩ 5V SEC-SGND R3N (120/N)kΩ R32 (120/N)kΩ R31 (120/N)kΩ *See Table 1 The Power Behind Performance Rev 1.0 10/15 vicorpower.com Applications Engineering: 800 927.9474 Page 14