DEMO CIRCUIT 453B QUICK STARTLT1970A GUIDE LT1970A Power Amplifier with Adjustable Current Limiting DESCRIPTION Demonstration circuit 453B is useful for evaluating the LT1970A, a power amplifier with adjustable current limiting. The demo circuit is available in two versions; DC453B-A with up to 500mA of output current and DC453B-B for applications with up to 5 Amps of output current. For the 5 Amp version a Class B MOSFET based current boost stage has been added to the output section with current limit control still provided by the LT1970A. The maximum output current of the board is set by two on-board potentiometers to permit independent control of the sinking and sourcing current limit. The current limit adjustment can also be provided by external voltage sources. Symmetrical sourcing and sinking current limit with a single control is also possible. LEDs provide an indication of faults detected by the LT1970A. Separate indicators illuminate when the amplifier enters sourcing or sinking current limit and if the LT1970A overheats and enters thermal shutdown protection. Several jumpers enable flexible amplifier operation. Configurations include: Single or dual power supplies Separate or common input stage and power output stage supplies AC or DC coupled inputs Non-Inverting gains of 1 or 2, Inverting gain of –1 Separate or common current limit control Design files for this circuit board are available. Call the LTC factory. , LTC and LT are registered trademarks of Linear Technology Corporation. ThinSOT and PowerPath are trademarks of Linear Technology Corporation. TYPICAL PERFORMANCE SUMMARY TA = 25°C, Common ±12V Supplies SYMBOL PARAMETER VSUPPLY Power Supply Range IOUT Adjustable Output Current Limit Range BWS Small Signal –3dB Bandwidth BWL SR VSATH Large Signal –3dB Bandwidth Slew Rate Output Sat Voltage High CONDITIONS Single Supply Dual Supply DC453B-A (LT1970A basic amplifier), Vcc ≥ 8V DC453B-B (Boosted) DC453B-A (LT1970A basic amplifier) AV= +1, Vout=200mVP-P, RLOAD=100Ω, DC453B-B (Boosted) AV= +1, Vout=200mVP-P, RLOAD=10Ω DC453B-A (LT1970A basic amplifier) AV= +1, Vout=20VP-P, RLOAD=100Ω DC453B-B (Boosted) AV= +1, Vout=10VP-P, RLOAD=10Ω, DC453B-A (LT1970A basic amplifier), VSAT=V+VOUT Common ±12V Supplies, RLOAD=250Ω Common ±12V Supplies, RLOAD=25Ω Vcc/Vee=±12V and V+/V-=±5V, RLOAD=100Ω Vcc/Vee=±12V and V+/V-=±5V, RLOAD=10Ω MIN 8 ±8 ±4 ±0.04 TYP MAX 36 ±18 ±500 ±5 UNITS V V mA A 1.6 MHz 7.2 KHz 58 KHz 7 1.6 KHz V/μS 1.4 2.1 0.1 0.8 V V V V 1 LT1970A TYPICAL PERFORMANCE SUMMARY TA = 25°C, Common ±12V Supplies SYMBOL PARAMETER VSATL IS Output Sat Voltage Low Total Quiescent Supply Current CONDITIONS DC453B-B (Boosted), See Operational Notes DC453B-A (LT1970A basic amplifier), VSAT= VOUTVCommon ±12V Supplies, RLOAD=250Ω Common ±12V Supplies, RLOAD=25Ω Vcc/Vee=±12V and V+/V-=±5V, RLOAD=100Ω Vcc/Vee=±12V and V+/V-=±5V, RLOAD=10Ω MIN DC453B-B (Boosted), See Operational Notes No Load DC453B-A (LT1970A basic amplifier) DC453B-B (Boosted) TYP MAX UNITS 2.1 2.8 0.3 1.3 V V V V 9 12 mA mA QUICK START PROCEDURE Demonstration circuit 453B is easy to set up to evaluate the performance of the LT1970A. Before applying power to the amplifier, configure all on-board jumpers for the desired operation. Figure 1 provides an overview of how JP1: Input Signal Coupling, AC or DC the placement of each of the jumpers adjusts the configuration. Position each jumper for the following results: DC coupling, non-inverting, applies the input signal directly to the amplifier + input with a 5KΩ input impedance, inverting, directly connects to a 10KΩ resistor to the amplifier – input. AC coupling connects the input signal through a series 10μF capacitor. Depending on the amplifier topology the lower –3dB corner frequency is in the range of 1.6Hz to 6.2Hz. JP2: Inverting (INV) or Non-Inverting (NI) Directs the input signal for an Inverting or Non-Inverting amplifier. DUAL sets the DC bias of the inputs and output to ground when symmetrical dual + and - power supplies are used. SINGLE sets the DC bias of the inputs and output to ½ Vcc when a single power supply is used. This setting also biases the inputs and output to the midpoint of asymmetrical dual supplies. Removing the shunt from this jumper can allow the power amplifier to bias at the same dc potential as the input signal for DC coupled single supply uses. JP4: Gain Configuration Setting The four positions of this jumper configure the amplifier to one of three gain values. The inset diagram on the schematic, Figure 4, shows how the amplifier feedback is arranged for each jumper position. A small table is also included on the printed circuit board to serve as a ready reference for the jumper settings. The jumper position shorting pins 2 and 3 provides the same configuration as shorting pins 3 and 4. JP5: Separate (S) or Common (C) Current Limit Control JP3: Input biasing for SINGLE or DUAL Power Supplies Separate (S) position allows for the independent setting of the amplifier sourcing current limit and sinking current 2 LT1970A limit through two 10K potentiometers and an on-board 5V regulator. Any voltage between 0V and 5V applied to the LT1970A pins VCSRC and VCSNK sets the output current limit value. Common (C) position connects the VCSRC and VCSNK input pins together to force the sourcing and sinking current limit values to be the same. With this setting, only the potentiometer labeled VCSRC adjusts the current limit control voltage. JP6: Vee biasing for SINGLE or DUAL Power Supplies SINGLE setting connects the Vee supply of the LT1970A directly to ground. DUAL setting connects the Vee supply to the VEE input jack. . With the Common (COM) selection just one power source, a single positive supply, or one pair of plus and minus supplies, is required. This supply powers both JP7: Common (COM) or Separate (SEP) Power Supplies the input stage supplies of the LT1970A, Vcc and Vee, and the output stage supplies, V+ and V-. With the Separate (SEP) selection the output stage supplies must be provided separately to the V+ and Vinput jacks. This feature reduces power dissipation in the output stage by running the supplies at a lower value than the main amplifier input stage. COM S C SEP Note proper shunt orientation. JP7 JP5 Separate or Common Source and Sink Current Limit Control Common or Separate Input Stage and Output Stage Supplies SINGLE DUAL JP6 Single Supply (LT1970 Vee=0V) or Dual Supply (LT1970 Vee=Vee Voltage) DC AC JP1 DC or AC Coupled Input Gain Setting Table JP4 INV JP2 NON SINGLE JP3 DUAL 5 4 3 2 1 Amplifier Gain Configuration Inverting or NonSingle Supply (DC Vout=Vcc/2) or Inverting Dual Supply (DC Vout=0V) Amplifier Figure 1. DC453B Jumper Configuration 3 LT1970A POWER CONNECTIONS Figure 2 shows how to properly connect power to the 453B demo circuit. Dual Supplies Separate Dual Supplies Single Supply Figure 2. Power Supply Connections OPTIONAL EXTERNAL CONNECTIONS Several test point turrets have been added, see Figure 3, to make it easy to use external equipment to control the operation of the power amplifier. External Enable(5V)/Disable(0V) Pulse Error Flag Monitoring Thermal Shutdown (TP14) Sink Current Limit (TP15) Source Current Limit (TP16) TP10 External Current Limit Control (Use Source Supply Only for Single Symmetrical Current Limit Control) Sink 0V to 5Vdc TP3 Source 0V to 5Vdc TP4 Manual Current Source Limit Adjustments Sink TP11 Input Signal J6 J4 Load Output Signal Figure 3. External Control Options 4 LT1970A OPERATIONAL NOTES Minimum Supply Voltage The LT1970A can operate with a total supply voltage of only 5 Volts. For convenience, a 5V regulator is included on DC453B to provide the control voltage for the current limit adjustments. To keep this regulator properly biased the minimum positive Vcc supply must be at least 8 Volts when using either a single or dual power supply. Lower supply voltage is possible if external current limit control voltages are provided. Current Limit Control To ensure proper operation of the LT1970A two 100kΩ resistors to ground are connected to the two current limit control inputs. These resistors prevent open circuit control inputs with jumper JP5 removed. The effect of these resistors slightly attenuates the current limit control voltages provided by the on-board potentiometers. With separate limit control, the maximum voltage is 4.6V. When tied together for common control the maximum voltage is 4.2V. The actual current limit of DC453B is actually slightly greater than the expected nominal value at higher output current levels (greater than 400mA for the –A version and 4A for the –B version). The reason for this is the inclusion of diode package D5. The back-to-back diodes across the current sense inputs prevent erratic behavior in the unlikely event of an abrupt output short circuit condition. These diodes limit the maximum voltage difference seen at the sense amplifier inputs. When the voltage across the sense resistor, Rsense, exceeds 0.4 Volts, the diodes begin to conduct current and decrease the actual voltage difference seen by the sense amplifier. Boosted Current Version DC453B-B contains complimentary P and N channel power MOSFETs for output current up to ±5A. The same easy voltage control of the output current is provided by the LT1970A. The current boost stage is a class B design intended for DC and low frequency applications. The crossover distortion of this typical Class B design is apparent at frequencies greater than 7kHz. Above this frequency, the total time in crossover becomes 10% or more of the period of a sine wave input. The frequency response of the current boosted amplifier will vary as a function of the load resistance. Resistor R9, 100Ω, and the load resistor create an attenuation network inside the feedback loop of the amplifier. This causes the LT1970A to run at a higher closed loop gain than the overall amplifier gain, limiting the observed output 1 ⎛ R ⎞ 2πRF C 24 • ⎜⎜ 1 + 9 ⎟⎟ ⎝ Rload ⎠ closed loop frequency response. The –3dB corner frequency of the boosted amplifier is: F−3dB = Where RF (10KΩ) and C24 (220pf) are feedback components already provided on the board. Refer to the Figure 4 schematic. With no load, the non-inverting unity gain bandwidth is 72kHz. Depending on signal levels the usable bandwidth may be less due to the 1.6V/μs slew rate. The large power MOSFETs in the output stage can pull the output voltage very near the supply voltage rails. This can cause the sense amplifier inputs to exceed their input common mode voltage range, which is 1V away from either the Vcc or Vee supply rail. This can cause what appears to be a latch-up condition where the output goes to one rail or the other and illuminates the current limit indicators. Reducing the input voltage and cycling the power supplies will reset the amplifier back to normal. To prevent this from occurring, places for resistor divider networks to reduce the voltages seen at the sense amplifier inputs are provided. These are resistors R12 through R15 on the board. The identical divider networks should ensure that the peak voltages at the sense amplifier inputs are never within 1 Volt of the Vcc or Vee supply rails. 5 A B C D C16 10uF 35V 7 6 3 DUAL SINGLE NC NC NC U2 LTC3010EMS8E-5 + 8 VEE 4 GND 5 OUT C14 1uF 2 JP2 +5V R26 10K DC453B-A NON BOOSTED DC453B-B BOOSTED Assembly Type 100 0 JUMPER R9, R10, R11 25V C17 10uF INV NON INPUT_OPA TP1 * VERSION TABLE VEE_DEVICE 2 1 5 JP4 1 2 3 4 5 3 10uF AC R20 4.99K 2 JP3 SHDN 1uF JP6 2 2 DC SENSE GND IN 25V C1 JP1 1 C15 R16 2K VCC DUAL SINGLE 2.5K R19 BNC TP18 TP19 TP20 TP21 TP22 R17 4.99K R18 4.99K VCC J1 (OPT.) INPUT 1 3 1 3 VR1 10K VR2 10K 1 R12,R14 10K R2 TP4 Q1, Q2 4 VCC TBD C2 10K RF * * 2 1 R21 R3 NOT 0 JUMPER INSTALLED INSTALLED 0 JUMPER 1 OHM >=0.5W R13,R15 TBD * R14 TBD * R12 R30 100 3 D5 BAV99 3 3 NOT INSTALLED NOT INSTALLED R3, R21 R22, R23 TBD * R15 * * R9 1K (OPT.) C12 TBD * R11 TP7 GND J6 VEE TP9 THIS CIRCUIT IS PROPRIETARY TO LINEAR TECHNOLOGY AND SUPPLIED FOR USE WITH LINEAR TECHNOLOGY PARTS. 2 LINEAR TECHNOLOGY HAS MADE A BEST EFFORT TO DESIGN A CIRCUIT THAT MEETS CUSTOMER-SUPPLIED SPECIFICATIONS; HOWEVER, IT REMAINS THE CUSTOMER'S RESPONSIBILITY TO VERIFY PROPER AND RELIABLE OPERATION IN THE ACTUAL APPLICATION. COMPONENT SUBSTITUTION AND PRINTED CIRCUIT BOARD LAYOUT MAY SIGNIFICANTLY AFFECT CIRCUIT PERFORMANCE OR RELIABILITY. CONTACT LINEAR TECHNOLOGY APPLICATIONS ENGINEERING FOR ASSISTANCE. COM PCB DES. TIM R. AK SCALE = NONE APP ENG. 10K 10K - + 10K DUAL SINGLE SUPPLY - + 1 VEE VCC V- V+ C22 10uF 35V C20 10uF 35V C10 10uF 35V C8 10uF 35V +2 JP2 10K 4-5 10K 2-3 - + - + 10K DUAL SUPPLY ONLY 10K DUAL SINGLE SUPPLY 0.1uF C23 C21 0.1uF C11 0.1uF C9 0.1uF DATE: N/A 1 LT1970A DEMO CIRCUIT 453B Wednesday, November 28, 2012 IC NO. SHEET 1 POWER OP AMP WITH ADJUSTABLE CURRENT LIMIT SIZE DATE 11-28-12 OF 1 1 REV. 1630 McCarthy Blvd. Milpitas, CA 95035 Phone: (408)432-1900 www.linear.com Fax: (408)434-0507 LTC Confidential-For Customer Use Only INV NON JP2 INV NON TECHNOLOGY IN IN +2 -1, +1 -1, +1 3-4 4-5 +2 -1, +1 -1, +1 2-3 AC GAIN +1 DC GAIN 1-2 + + + + TIM R. APPROVED JP4 JP4 SETTINGS VEE -18V MAX E3 E2 GND VCC +18V MAX E1 V-18V MAX E5 GND E6 V+ +18V MAX E4 PRODUCTION DESCRIPTION REVISION HISTORY JP4 SETTING DIAGRAM DUAL SINGLE SUPPLY V- 1 __ V+ REV ECO TITLE: SCHEMATIC 10K 3-4 JP2 INV NON 10uF INV NON JP2 1-2 SEP APPROVALS IN IN JP7 OUTPUT SUPPLIES VCC 2 OUT FET D FET_V- OUTPUT J4 FET_V- NFET J2 (OPT.) OUTPUT MONITOR BNC S * IRF530N D Q2 IRF9530N PFET * Q1 D S CUSTOMER NOTICE TP8 OUTPUT TBD * C13 G G * R10 TP6 FET_V+ FET_V+ 1/2W * R1K_LOAD * R_SENSE 1/2W R8 *100 TP5 OPA OUT B A * R23 TBD 3 R13 220pF C24 OPA OUT TBD TBD TBD * R22 0.1 OHM >=3W C12, C13 C18 TBD 100K R29 R_SENSE 3 0.1uF C7 TP13 VCC R5 R6 R7 1.5K 1.5K 1.5K U1 LT1970A JP5 S C B A 10uF 35V TP3 R28 100K VCSNK C5 0.1uF -IN COMMON +IN C6 R4 10K VCSRC/VCLCONT 10K R1 8 14 9 15 NOT NOT NOT INSTALLED INSTALLED INSTALLED NOT INSTALLED INSTALLED INSTALLED R8 VCSRC +5V MAX 2 0-> +5V 2 C4 10uF 35V VCSNK TP17 VEE_DEVICE VEE D4 BAT54WS TP2 +IN VEE_DEVICE R27 4.99K TP10 TP14 TP15 ISRC TP16 ISNK TSD ENABLE IN 4 7 VCC D2 GND TP12 3 1 3 1 SENSE- INPUT TP11 3 1 CW INCREASE CW INCREASE + 5 13 17 ISNK D1 18 TSD VCSRC 6 5 TSD AMB ISNK AMB ISRC RED 6 19 4 3 D3 16 ISRC FILTER 5 ENABLE VEE VEE VEE VEE 1 10 11 20 2 VCSNK 12 SENSE+ 4 V+ V- 2 2 1 + A B C D