Supertex inc. AN-H59 Application Note High Voltage DC/DC Converter for Supertex Ultrasound Transmitter Demoboards By Afshaneh Brown, Applications Engineer, and Jimes Lei, Applications Manager Introduction The Supertex AN-H59DB1 demoboard is a high voltage DC/DC converter. It can provide up to +90V voltage supply for VPP and -90V for VNN. It also provides +8.0 to +10V voltage supply for VDD, floating power supplies of VNN +8.0 to VNN +10V for VNF and VPP -8.0 to VPP -10V for VPF. The input supply voltage is 12V. To accommodate all three demoboards, the AN-H59DB1 demoboard has adjustable VPP, VNN, VDD, VPF and VNF. The purpose of the AN-H59DB1 is to aid in the evaluation of the three transmitter demoboards. The intention of this application note is to provide a general circuit description on how each of the output voltages is generated. The AN-H59DB1 circuitry consists of two high voltage PWM Current-Mode controllers, a DC/DC transformer driver, and three low dropout regulators. The Supertex AN-H59DB1 uses a high-voltage, current mode, PWM controller boost topology to generate +15 to +90V and a high-voltage current mode PWM controller buck-boost topology to generate -15 to -90V power supply voltage for Supertex HV738DB1 and HV748DB1 ultrasound transmitter demoboards. The VSUB pin on the HV738DB1 and HV748DB1 can either be connected to the most positive supply voltage on the demoboard, or can be left floating. Each of the transmitter demoboards has slightly different operating voltages as summarized below. Board VPP VNN VDD VPF VNF HV738DB1 +65V -65V +8.0V VPP -8.0V VNN +8.0V HV748DB1 +75V -75V +9.0V VPP -9.0V VNN +9.0V To power up the AN-H59DB1, ensure that the 3.3V power supply will be powered up first, and then the 12V power supply. The sequences on the HV738DB1 and HV748DB1 took into consideration using the protection diodes on each power line. The circuit is shown in Figure 6, the component placement in Figure 5, and the bill of materials is at the end of this application note. Application Circuit Supertex inc. ● 1235 Bordeaux Drive, Sunnyvale, CA 94089 ● Tel: 408-222-8888 ● www.supertex.com AN-H59 VPP Circuit Description The circuit in Figure 1 shows U5, the Supertex high voltage current mode PWM controller, being used to generate the high voltage power supply for VPP. The maximum output power for VPP was set for 10mA at 90V, which is 900mW. With an input voltage of 12V, a converter frequency of 110 kHz with a 100µH inductor was chosen to provide the desired output power. The converter frequency is set by an external resistor, R20, across OSCIN and OSCOUT pins of U5. A 154kΩ resistor will set the frequency to about 110 kHz. R24 is the current sense resistor. 2.2Ω was used to set the maximum peak current limit to about 450mA. An RC filter, R23 and C15, is added between the current sense resistor and the current sense terminal pin 3 of U5. This reduces the leading edge spike on R24 from entering the current sense pin. Inductor L1 is being charged from the 12V input by M3. When M3 turns off, the energy in L1 is discharged into C16, which is the VPP output through D8. The VPP voltage is divided down by feedback resistors R25, R26, and R27. The wiper of R26 is connected to pin 14 of U5. The overall converter will regulate the voltage on pin 14 to 4.0V. Different VPP output voltages can be obtained by adjusting R26. When the wiper for R26 is set to the top, VPP can be calculated as: V = V x R25 + R26 + R27 PP FB ( R26 + R27 ) where VFB is 4.0V VPP = 4.0V x + 14.3k ( 232k100k+ 100k ) = 12.1V + 14.3k When the wiper for R26 is set to the bottom, VPP can be calculated as: V = V x R25 + R26 + R27 PP FB ( VPP = 4.0V x ) R27 100k + 14.3k ( 232k +14.3k ) = 96.9V By adjusting potentiometer R26, VPP meets the adjustable target range of 15 to 90V. Comparator U6 will turn on LED D7 when the VPP output is out of regulation due to excessive load. During initial power up, C16 will be at 0V. D7 is therefore expected to be on until C16 is charged to the desired regulation voltage. Figure 1: Adjustable VPP Power Supply VIN = 12V R20 154kΩ 8 OSCIN OSCOUT C12 10µF 7 L1 100µH 4 M3 TN2510 6 VDD R21 383kΩ C13 0.1µF VIN 1 10 5 D7 LED R22 3.32kΩ 2 VIN 9 1 8 U6 LM2903 4 + U5 OUT HV9110NG BIAS SENSE C14 1.0µF DISCH Supertex inc. FB +15V to +90V GND R24 2.2Ω 11 R26 100kΩ 12 R27 14.3kΩ COMP RESET 14 C16 2.2µF R25 232kΩ GND SHUTDOWN 13 VPP R23 1.0kΩ C15 470pF VREF 3 2 3 D8 MMBD914 ● 1235 Bordeaux Drive, Sunnyvale, CA 94089 ● Tel: 408-222-8888 ● www.supertex.com 2 AN-H59 VNN Circuit Description The circuit in Figure 2 shows U7, the Supertex high voltage current mode PWM controller, being used to generate the high voltage power supply for VNN. The function of U7 is very similar to what was described in the VPP circuit description for U5. However, in this circuit a negative voltage is generated from a positive input voltage source, therefore requiring a buck-boost topology. The maximum output power for VNN was set for -10mA at -90V which is 900mW. With an input voltage of 12V, a converter frequency of 110 kHz with a 100µH inductor was chosen to provide the desired output power. Inductor L2 is being charged from the 12V input by the parallel combination of M6 and M7. When M6 and M7 turn off, the energy in L2 is discharged into C23, which is the VNN output through D10. M6 and M7 are high voltage P-channel MOSFETs. U7 is designed to drive a high voltage N-channel MOSFET. The drive output for U7 therefore needs to be inverted. This is accomplished by M4 and M5. The feedback voltage that U7 detects on pin 14 is +4.0V. The VNN that needs to be sensed is a negative voltage. A circuit is needed to make sure the feedback voltage is positive. This is consists of Q4, Q5, R33, R34, R35, R37, and R38. Q4 becomes a constant current sink set by the VNN voltage and R35. The same current will be flowing through R33 and R34. The voltage on the base of Q5 will be VIN minus the voltage drop across the sum of R33 and R34. By varying R34, the base voltage on Q5 will change. Q5 becomes a constant current source with a value set by its base voltage and R37. The current source of Q5 is going into R38, which creates a positive voltage that is now proportional to the magnitude of VNN. R35 VNN = VBE - ( ) x (VBE + VFB x R37 ), R33 + R34 R38 where VBE = 0.6V, VFB = 4.0V. When R34 is set to 100k, VNN is calculated to be: 273k VNN = 0.6V - ( ) x (0.6V + 4.0V x 14.7k ) 4.99k + 100k 40.2k = -4.0V When R34 is set to 0k, VNN is calculated to be: 273k ) x (0.6V + 4.0V x 14.7k ) VNN = 0.6V - ( 4.99k + 0k 40.2k = -97.4V By adjusting potentiometer R34, VNN meets the adjustable target range of -15 to -90V. Comparator U8 will turn on LED D9 when the VNN output is out of regulation due to excessive load. During initial power up, C23 will be at 0V. D9 is therefore expected to be on until C23 is charged to the desired regulation voltage. Figure 2: Adjustable VNN Power Supply VIN = 12V 8 6 C17 10µF R29 383kΩ VIN = 12V R30 3.32kΩ 9 1 8 U8 4 LM2903 + OUT 4 U7 HV9110NG M5 TN2106K1 BIAS VREF GND DISCH SENSE 3 3 2 13 C19 1.0µF R34 100kΩ 7 M4 TP2104K1 R33 4.99kΩ M6, M7 TP2510N8 X2 D10 MMBD914 R37 14.7kΩ Q5 FMMT551 Q4 FMMT494 R38 40.2kΩ R35 237kΩ VNN 10 5 D9 LED OSCOUT VDD 2 VIN 1 C18 0.1µF OSCIN C21 10µF C20 10µF R28 154kΩ 14 Supertex inc. COMP FB SHUTDOWN 11 RESET 12 R31 1.0kΩ C22 470pF L2 100µH R32 2.2Ω C23 2.2µF -15V to -90V GND R36 10kΩ ● 1235 Bordeaux Drive, Sunnyvale, CA 94089 ● Tel: 408-222-8888 ● www.supertex.com 3 AN-H59 VPF and VNF Circuit Description The three transmitter demoboards require two floating low voltage supplies, VPF and VNF. The floating supplies need to be adjustable to accommodate the different operating requirements for the three different boards. The VPF is 8.0 to 10V below the high voltage VPP positive supply. The VNF is 8.0 to 10V above the high voltage VNN negative supply. The two floating supplies are generated by using two isolated transformers, T1 and T2, and an isolated transformer driver, U1, as shown in Figure 4. Both outputs utilize adjustable low dropout linear regulators, U2 and U3, as shown in Figure 3. U2 and U3 are both Linear Technology LT1521, which has a reference voltage of 3.75V on the ADJ pin. For VPF, resistors R6, R7, and R8 set the output VPF voltage. R7 is a potentiometer for adjusting VPF. VPF can be calculated with the following equation: V = V x R6 + R7 + R8 PF ( ADJ ) R7 + R8 When R7 is set to 20kΩ, VPF becomes: VPF = 3.75V x + 20k + 24.9k ( 45.3k20k ) = 7.53V + 24.9k ( 45.3k + 0k + 24.9k 0 +24.9k ) LED indicators, D5 and D11, start to turn on when the input current to U2 and U3 reaches an arbitrary value of 40mA. This is set by Q1 and R3 for VPF and Q2 and R9 for VNF. The input current can be calculated with the following equation: Input current = VEB = 0.5V = 41.3mA R 12.1Ω 50mA current limits are added to protect against output shorts. The current limiter is consists of a depletion-mode MOSFET and a series source resistor. The resistor sets the current limit and can be estimated with the following equation: RSERIES = When R7 is set to 0Ω, VPF becomes: VPF = 3.75V x Please note that the OUT pin on U2 is referenced to VPP, thereby setting VPF to be 8.0 to 10V below VPP. VNF can also be calculated in a similar manner using resistors R12, R13, and R14. Please note that the GND pin on U3 is referenced to VNN thereby setting VNF to be 8.0 to 10V above VNN. VTH x ( √I / I - 1) where, LIM DSS ILIM VTH = pinch-off voltage for M1 and M2: -2.5V ILIM = desired current limit: 50mA IDSS = saturation current for M1 and M2: 1.1A = 10.6V RSERIES = 39.3Ω. A 40.2Ω resistor was used. Figure 3: Adjustable VPF and VNF Power Supply R3 12.1Ω VIN = 12V 13 11 C1 10µF 4 R1 16.9kΩ R2 16.9kΩ 7 6 VIN COLA 3 SHUTDOWN RSL COLB 14 2 9 3 8 4 7 D1 MMBD914 Q1 FMMT551 C2 10µF D2 D1 CTX02-16076 MMBD914 U1 LT3439 M1 DN3525 R42 1.5kΩ R9 12.1Ω CT C11 470µF 5 SYNC 10 GND 1,16 PGND 2 9 3 8 4 7 D3 MMBD914 Q2 FMMT551 C5 10µF R43 1.5kΩ 8 R39 100kΩ R15 4.99kΩ 3,6,7 R11 40.2Ω GND R10 4.99kΩ 5 3,6,7 C6 10µF VPP R6 45.3kΩ R7 20kΩ IN OUT 1 U3 LT1521 ADJ 2 SHUTDOWN GND VFP VNF R12 45.3kΩ R13 20kΩ R14 24.9kΩ D4 D1 CTX02-16076 MMBD914 Supertex inc. +8.0 to +10V C4 10µF R8 24.9kΩ 8 R40 100kΩ D11 LED OUT 1 U2 LT1521 ADJ 2 5 SHUTDOWN IN C3 10µF D5 LED M2 DN3525 RT R4 40.2Ω ● 1235 Bordeaux Drive, Sunnyvale, CA 94089 ● Tel: 408-222-8888 ● www.supertex.com 4 +8.0 to +10V C7 10µF VNN AN-H59 VDD Circuit Description The VDD output voltage utilizes an adjustable low dropout linear regulator, U4 LT1521, as shown in Figure 4. The desired adjustable output voltage range is 8.0 to 10V to accommodate the different operating VDD voltages for the three different transmitter demoboards. The LT1521 has a reference voltage of 3.75V on the adj pin. Resistors R17, R18, and R19 set the output VDD voltage. R18 is a potentiometer for adjusting VDD. VDD can be calculated with the following equation: VDD = VADJ x + R18 + R19 ( R17R18 ) + R19 When R18 is set to 0Ω, VDD becomes: VDD = 3.75V x An LED indicator, D6, is included in case of excessive input, IIN, current. D6 is starts to turn on when the input current reaches an arbitrary value of 20mA. This is set by Q3 and R15. When the emitter-base junction of Q3 is forward biased (0.5V), Q3 will start to turn on, thereby forward biasing D6. The IIN value to turn D6 on can be calculated with the following equation: When R18 is set to 20kΩ, VDD becomes: VDD = 3.75V x + 24.9k ( 45.3k 0+ +0k24.9k ) = 10.6V IIN = + 24.9k ( 45.3k20k+ 20k ) = 7.53V + 24.9k VEB 0.5V = = 20.6mA R15 24.3Ω Figure 4: Adjustable VDD Power Supply VIN = 12V R15 24.3kΩ Q3 FMMT551 C8 10µF 3.3V Input Terminal 8 R41 100kΩ R16 3.32kΩ C9 10µF D6 LED The AN-H59DB1 has a 3.3V input terminal that is directly connected to the output terminal, VCC. There is no circuitry on this board that uses the 3.3V supply. It is only there as a convenient connection to the 8-pin header. VCC is the logic supply voltage for HV738DB1 and HV748DB1 and can operate from 1.2 to 5V. However, most users will operate VCC at either 3.0 or 3.3V. 5 3, 6, 7 OUT IN U4 LT1521 ADJ SHUTDOWN GND 1 2 VDD R17 45.3kΩ R18 20kΩ C10 10µF R19 24.9kΩ +8.0 to 10V GND Input and Output Power The output voltages from the AH-H59DB1 are all generated from the 12V input line. With no load on the outputs, the measured input current was about 70mA. This input current can vary from board to board due to variations in the isolated transformer. The maximum output power is: POUT(MAX) = PVPP(MAX) + PVNN(MAX) + PVPF(MAX) + PVNF(MAX) + PVDD(MAX) POUT(MAX) = 0.9W + 0.9W + 0.4W + 0.4W + 0.2W POUT(MAX) = 2.8W Under this condition, the 12V input current was measured to be 340mA. Input power is therefore 4.08W. This gives an approximate overall efficiency of 69% at full load. Supertex inc. ● 1235 Bordeaux Drive, Sunnyvale, CA 94089 ● Tel: 408-222-8888 ● www.supertex.com 5 AN-H59 VPF and VNF Output Current The AN-H59DB1 can supply more than 40mA of current for the VPF and VNF outputs. The INF and IPF input currents for the HV738 or the HV748 can be found in their respective data sheet but are summarized below: Part # IPF-mode 4 INF-mode 4 HV738 30mA 12mA HV748 50mA 25mA This is for continuous 5.0 MHz operation. For ultrasound, the high voltage transmitter is operating at very low duty cycles; 1% or lower. At a 1% duty cycle, the average current is expected to be a 100 times lower. The 40mA output current capability on the AN-H59DB1 is more than sufficient to power up the HV738 or the HV748. Conclusion The main purpose of AN-H59DB1 power supply demoboard is to help the evaluation of the Supertex HV738DB1 and HV748DB1 demoboards by reducing the number of power supplies needed. The AN-H59DB1 was designed to operate from a single 12V input which should be commonly available in any engineering laboratory. The five on-board LEDs allow the user to quickly determine whether there is an overload condition on each of the supply lines. The five potentiometers allow the user to easily adjust each supply to meet their particular needs. Figure 5: AN-H59 Component Placement Supertex inc. ● 1235 Bordeaux Drive, Sunnyvale, CA 94089 ● Tel: 408-222-8888 ● www.supertex.com 6 AN-H59 Figure 6: AN-H59 Circuit Schematic R20 154kΩ 8 D7 LED BIAS 10 8 R25 232kΩ N/C 4 R26 100kΩ 13 COMP SHUTDOWN C14 10µF 14 RESET FB R3 12.1Ω 13 11 C1 10µF 1 R1 16.9kΩ 7 R1 16.9kΩ 6 VIN COLA D1 MMBD914 3 2 SHUTDOWN RSL COLB 14 8 4 7 C2 10µF CT C11 470pF 5 SYNC 10 GND 1, 16 PGND R5 4.99kΩ 9 3 8 4 D5 LED C5 10µF R43 1.5kΩ D11 LED GND 8 6 C17 10µF C18 0.1µF D9 LED 1 10 5 9 8 U8 LM2903 OSCIN OSCOUT OUT U7 HV9110NG VIN R6 45.3kΩ C4 10µF R7 20kΩ GND R8 24.9kΩ 8 OUT 5 3, 6, 7 VPF VNF 1 U3 LT1521 IN ADJ 2 C6 10µF R12 45.3kΩ R13 20kΩ SHUTDOWN GND C7 10µF Q3 FMMT551 VPP VPF COMP SHUTDOWN 14 FB M5 TN2510 D10 MMBD914 RESET 3 11 L2 100µH R31 1.0kΩ R16 3.32kΩ C9 10µF 5 3, 6, 7 OUT IN U4 LT1521 ADJ SHUTDOWN GND GND J1 VDD 1 2 R17 14.3kΩ R18 20kΩ VCC 1 R36 10kΩ 12 R41 100kΩ VDD C23 2.2µF R32 2.2Ω C22 470µF VNN R37 14.7kΩ Q4 FMMT494 R38 40.2kΩ R35 237kΩ M6, M7 TN2510 8 D6 LED C10 10µF GND R19 24.9kΩ VCC Supertex inc. VNF Q5 FMMT551 R34 100kΩ VREF N/C R33 4.99kΩ C21 10µF 4 GND SENSE 13 C19 1.0nF 8 R14 24.9kΩ M4 TN2510 R15 24.3Ω C8 10µF 2 SHUTDOWN 7 BIAS 3 + - 2 4 C3 10µF C20 10µF VDD 2 R29 383kΩ 1 IN VNN R28 154kΩ R30 3.32kΩ U2 LT1521 1 D4 MMBD914 12V 3.3V 5 3, 6, 7 R40 100kΩ R10 4.99kΩ OUT ADJ R11 M2 DN3525 40.2Ω 7 T2 CTX02-16076 8 Q2 FMMT551 D3 MMBD914 2 R42 1.5kΩ R9 12.1Ω RT R27 14.3kΩ 12 R39 100kΩ Q1 FMMT551 T2 D2 CTX02-16076 MMBD914 U1 LT3439 11 R4 M1 DN3525 40.2Ω 9 3 R24 2.2kΩ C15 470pF 3 + - 2 U6 LM2903 C16 2.2µF GND 9 1 3 SENSE VPP M3 TN2510 R23 1.0kΩ VREF 5 R22 3.32kΩ 4 U5 OUT HV9110NG 1 C13 0.1µF D8 MMBD914 VDD 2 VIN R21 383kΩ L1 100µH OSCOUT 7 OSCIN 6 C12 10pF ● 1235 Bordeaux Drive, Sunnyvale, CA 94089 ● Tel: 408-222-8888 ● www.supertex.com 7 AN-H59 Bill of Materials Reference Description Package Manufacturer Part No. C1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 17, 20, 21 Chip Capacitor, 10µF, 16V 1206 Any --- C11, 15, 22 Chip Capacitor, 470pF, 100V 805 Any --- C13, 18 Chip Capacitor, 0.1µF, 25V 805 Any --- C14, 19 Chip Capacitor, 1.0nF, 50V 805 Any --- C16, 23 Chip Capacitor, 2.2µF, 100V 1210 Any --- R1, 2 16.9kΩ, Chip Resistor 805 Any --- R3, 9 12.1Ω, Chip Resistor 805 Any --- R4, 11 40.2Ω, Chip Resistor 805 Any --- R5, 10, 33 4.99kΩ, Chip Resistor 805 Any --- R6, 12, 17 45.3kΩ, Chip Resistor 805 Any --- R7, 13, 18 20kΩ, Potentiometer --- Any --- R8, 14, 19 24.9kΩ, Chip Resistor 805 Any --- R15 24.3Ω, Chip Resistor 805 Any --- R16, 22, 30 3.32kΩ, Chip Resistor 805 Any --- R20, 28 154kΩ, Chip Resistor 805 Any --- R21, 29 383kΩ, Chip Resistor 805 Any --- R23, 31 1.02kΩ, Chip Resistor 805 Any --- R24, 32 2.20Ω, Chip Resistor 1206 Any --- R25 232kΩ, Chip Resistor 0805 Any --- R26, 34 100kΩ, Potentiometer --- Any --- R27 14.3kΩ, Chip Resistor 0805 Any --- R35 237kΩ, Chip Resistor 0805 Any --- R36 10.2kΩ, Chip Resistor 0805 Any --- R37 14.7kΩ, Chip Resistor 0805 Any --- R38 40.2kΩ, Chip Resistor 0805 Any --- R39, 40, 41 100kΩ, Chip Resistor 0805 Any --- R42,43 1.5kΩ, Chip Resistor 1206 Any --- L1,2 Inductor, 100µH --- Cooper Electronic SD3814-101-R D1, 2, 3, 4, 8, 10 100V, Fast Recovery Diode SOT-23 Fairchild MMBD914 D5, 6, 7, 9, 11 Red LED 0805 Lumex SML-LXT0805SRW Q1, 2, 3, 5 PNP, 60V, Bipolar Transistor SOT-23 Zetex Inc FMMT551TA Q4 NPN, 120V, Bipolar Transistor SOT-23 Zetex Inc FMMT494TA U1 IC, Low Noise Transformer Driver 16-TSSOP Linear Technology LT3439EFE#PBF U2, 3, 4 IC, Adjustable Linear Regulator SO-8 Linear Technology LT1521CS8#PBF Supertex inc. ● 1235 Bordeaux Drive, Sunnyvale, CA 94089 ● Tel: 408-222-8888 ● www.supertex.com 8 AN-H59 Bill of Materials (cont.) Reference Description Package Manufacturer Part No. U5, 7 High-voltage current-mode PWM controller SO-14 Supertex Inc. HV9110NG-G U6, 8 IC, Dual Voltage comparator SO-8 Texas Instruments LM2903DR T1, 2 Transformer --- Cooper Electronic CTX02-16076 M1, 2 MOSFETs Depletion Mode, N-channel, 250V SOT-89 Supertex Inc. DN3525N8-G M3 MOSFET Enhancement Mode, N-channel 100V SOT-89 Supertex Inc. TN2510N8 M4 MOSFET Enhancement Mode, P-channel 40V SOT-23 Supertex Inc. TP2104K1 M5 MOSFET Enhancement Mode, N-channel 60V SOT-23 Supertex Inc. TN2106K1 M6, 7 MOSFETs Enhancement Mode, P-Channel 100V SOT-89 Supertex Inc. TP2510N8 J1 8 Position, 0.100” Pitch, rectangular connector --- Tyco Electronic Amp 770602-8 Supertex inc. does not recommend the use of its products in life support applications, and will not knowingly sell them for use in such applications unless it receives an adequate “product liability indemnification insurance agreement.” Supertex inc. does not assume responsibility for use of devices described, and limits its liability to the replacement of the devices determined defective due to workmanship. No responsibility is assumed for possible omissions and inaccuracies. Circuitry and specifications are subject to change without notice. For the latest product specifications refer to the Supertex inc. (website: http//www.supertex.com) ©2012 Supertex inc. All rights reserved. Unauthorized use or reproduction is prohibited. 021312 Supertex inc. 1235 Bordeaux Drive, Sunnyvale, CA 94089 Tel: 408-222-8888 www.supertex.com