DESCRIPTION Demonstration circuit DC896 is a dual output regulator consisting of two constant-frequency step-down converters, based on the LTC6A- monolithic dual channel synchronous buck regulator. The DC896 has an input voltage range of.6v to 0V, with each regulator capable of delivering up to A of output current. The DC896 can operate in either Burst Mode or forced continuous mode. In shutdown, the DC896 can run off of less than 5 ua total. The DC896 is a very efficient circuit: up to DEMO CIRCUIT 896A DEMO BOARD LTC6AEFE- MANUAL LTC6AEFE- DUAL CHANNEL A 0V MONOLITHIC SYNCHRONOUS STEP-DOWN REGULATOR 90%. The DC896 uses the 8 Pin QFN LTC6AEFE- package, which has an exposed pad on the bottom-side of the IC for better thermal performance. These features, plus a programmable operating frequency range from 500 khz to 4 MHz ( MHz switching frequency with the RT pin connected to INTVcc), make the DC896 demo board an ideal circuit for use industrial or distributed power applications. Design files for this circuit are available at www.linear.com/demo. QUICK START PROCEDURE The DC896 is easy to set up to evaluate the performance of the LTC6A-. For a proper measurement equipment configuration, set up the circuit according to the diagram in Figure. NOTE: When measuring the input or output voltage ripple, care must be taken to avoid a long ground lead on the oscilloscope probe. Measure the input or output voltage ripple by touching the probe tip directly across the Vin or Vout and terminals. See the proper scope probe technique in figure. Please follow the procedure outlined below for proper operation.. Connect the input power supply to the Vin/Vin and terminals (Vin and Vin are separate nodes.). Connect the loads between the Vout and terminals. Refer to figure for the proper measurement equipment setup. Before proceeding to operation, insert jumper shunts XJP and XJP into the OFF positions of headers JP and JP, shunt XJP into the ON position (80 out-of-phase) of PHASE header JP, shunts XJP and XJP4 into the soft-start (SS) positions of headers JP and JP4, shunt XJP8 into the forced continuous mode (FCM) position of MODE header JP8, shunt XJP4 into the MHz position of the frequency (FREQ) header JP4, shunts XJP and XJP into the external (EXT) compensation positions of headers JP and JP, and shunt XJP6 into the Vout voltage options of choice of header JP6:.5V,.8V, or.5v, and a shunt into the Vout voltage option of choice:.5v (header JP5),.V (header JP5), or 5V (header JP7).. Apply 5.5V at Vins &. Measure both Vouts; they should read 0V. If desired, one can measure the shutdown supply current at this point. The supply current will be less than 5 ua in shutdown.. Turn on Vout and Vout by shifting shunts XJP and XJP from the OFF positions to the ON positions. Both output voltages should be within a tolerance of +/- %. 4. Vary the input voltages from 5.8V (the min. Vin is dependent on Vout) to 0V, and the load currents from 0 to A. Both output voltages should be within +/- % tolerance.
LTC6AEFE- 5. Set the load current of both outputs to A and the input voltages to 0V, and then measure each output ripple voltage (refer to figure for proper measurement technique); they should each measure less than 0 mvac. Also, observe the voltage waveform at either switch node (pins & 4 for reg. and & 4 for reg.) of each regulator. The switching frequencies should be between 800 khz and. MHz (T =.5 us and 0.8 us). To attain MHz operation, change the shunt position on header JP4. In all cases, both switch node waveforms should be rectangular in shape, and 80 outof-phase with each other. Change the shunt position on header JP to set the switch waveforms in phase with respect to each other. To operate the ckt.s in Burst Mode, change the shunt in header JP8 to the Burst Mode position. When finished, insert shunts XJP and XJP to the OFF position(s) and disconnect the power. 6. Regulators (VIN) and (VIN) are completely separated from each other; thus, they can be powered from different individual input supplies, as can the signal input supply. Of course, all the voltage requirements still must be met:.5v to 0V for the PVin pins and.6v to 0V for the SVin pin. Warning - If the power for the demo board is carried in long leads, the input voltage at the part could ring, which could affect the operation of the circuit or even exceed the maximum voltage rating of the IC. To eliminate the ringing, a small tantalum capacitor (for instance, AVX part # TPSY6M05R000) is inserted on the pads between the input power and return terminals on the bottom of the demo board. The (greater) ESR of the tantalum capacitor will dampen the (possible) ringing voltage caused by the long input leads. On a normal, typical PCB, with short traces, this capacitor is not needed. Table. Performance Summary (TA = 5 C) PARAMETER CONDITIONS VALUE Minimum Input Voltages.6V Maximum Input Voltages Run Output Voltage VOUT Regulation RUN Pin = RUN Pin = VIN VIN =.6V to 0V, IOUT = 0A to A 0V Shutdown Operating Typical Output Ripple VOUT VIN = V, IOUT = A (0 MHz BW) < 0mVP P Output Voltage VOUT Regulation VIN =.6V to 0V, IOUT = 0A to A Typical Output Ripple VOUT VIN = V, IOUT = A (0 MHz BW) < 0mVP P.5V ±% (.455V -.545V).8V ±% (.746V.854V).5V ±% (.45V.575V).5V ±% (.45V.575V).V ±% (.0V.99V) 5V ±% (4.85V 5.5V) Nominal Switching Frequencies RT Pin connected to 4k MHz RT Pin = MHz Channel : Vin = V, Vout =.8V, Fsw = MHz Iout <.5A Burst Mode Operation Channel : Vin = V, Vout =.V, Fsw = MHz Iout <.5A Output Current Thresholds Channel : Vin = V, Vout =.8V, Fsw = MHz Iout < A Channel : Vin = V, Vout =.V, Fsw = MHz Iout < 0.75 A Phase Phase Pin = Out-of-Phase Phase Pin = In Phase.V ±6%
LTC6AEFE- Figure. Proper Measurement Equipment Setup Figure. Measuring Input or Output Ripple
LTC6AEFE- Figure. LTC6A- DC896 Switch Operation V IN& = V, V OUT =.8V @ I OUT = A, V OUT =.V @ I OUT = A Forced Continuous Mode FSW = MHz External Compensation: Rithx = k, Cithx = 0 pf Trace : V SW (0V/div) Trace : V OUT AC Voltage (0mV/div AC) Trace : V SW (0V/div) Trace 4: V OUT AC Voltage (0mV/div AC) 4
LTC6AEFE- Figure 4. V OUT Load Step Response V IN = V, V OUT =.8V, A Load Step (0A <-> A) Forced Continuous Mode FSW = MHz External Compensation: Rith = k, Cith = 0 pf Trace : Output Voltage (00mV/div AC) Trace 4: Output Current (A/div) 5
LTC6AEFE- Figure 5. V OUT Load Step Response V IN = V, V OUT =.V, A Load Step (0A <-> A) Forced Continuous Mode FSW = MHz External Compensation: Rith = k, Cith = 0 pf Trace : Output Voltage (00mV/div AC) Trace 4: Output Current (A/div) 6
LTC6AEFE- Figure 6. LTC6A- DC896 Efficiency 7
LTC6AEFE- E0 CVCC uf TRACK E9 RTR 0 SS TRACK/SS TRACK JP CTR 4700pF CVCC uf CTR 4700pF TRACK/SS JP4 SS TRACK RTR 0 E TRACK PGOOD VOUT A VIN VIN E4 E6 E5 E E6.6V - 0V E [] + CIN5 uf 5V 74 [] + CIN6 uf 5V 74 COUT5 0uF 6.V 0805 RTR VOUT VO SELECT 4 6 ON OFF CIN uf 5V 0 CIN4 uf 5V 0 PHASE JP 5 JP6 VIN VIN CIN uf 5V 0 COUT uf 6.V 06 RPHMDE M R 4.8K % R5.K % R7 7.4K % R9 K % VIN VIN D R ON OFF CFFW 0pF MHz (INT.) RUN JP SVIN RUN VISHAY IHLP-00BZERR0M0 CC 0pF RITH K % RPG 00K CITH 0pF [] CIN5 AND CIN6 ARE INSERTED ON DC896A TO DAMPEN THE (POSSIBLE) RINGING VOLTAGE DUE TO THE USE OF LONG INPUT LEADS. ON A NORMAL, TYPICAL PCB, WITH SHORT TRACES, CIN5 AND CIN6 ARE NOT NEEDED. VIN VIN RPG 00K R M RUN C 0.uF SVIN L.uH VISHAY IHLP-00BZERRM0 RITH K % CC 0pF CUSTOMER NOTICE 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. RUN 4 6 JP D ITH JP MODE JP8 ON OFF VIN EXT INT 5 R4 84.5K % APPROVALS PCB DES. APP ENG. THIS CIRCUIT IS PROPRIETARY TO LINEAR TECHNOLOGY AND SUPPLIED FOR USE WITH LINEAR TECHNOLOGY PARTS. SCALE = NONE MI D CMDSH--TR BURST MODE SYNC SVIN CSVIN uf R0 6.7K % R6 8.7K % R8.5K % D4 RTR4 CMDSH--TR VOUT.5V.V 5V VIN JP5 JP5 JP7 FCM (FORCED CONTINUOUS MODE) TOM G. TITLE: SIZE N/A DATE: SCHEMATIC CSVIN uf COUT6 0uF 6.V 0805 VO SELECT R 0k TECHNOLOGY E8 E E E5 E7 E4 E PGOOD INTVcc.5V.8V.5V 8 BOOST VON U LTC6AEFE- BOOST VON VFB 0 5 SVIN VOUT A 0 S TRACK/SS PVIN PVIN PGOOD 8 9 RUN SW SW ITH 9 7 6 4 8 7 RT MODE/SYNC PGOOD PVIN PVIN TRACK/SS 4 5 4 6 6 7 RUN SW SW VFB 9 P.6V - 0V COUT uf 6.V 06 CIN uf 5V 0 NOTES: UNLESS OTHERWISE SPECIFIED, EXT INT ITH JP MHz L.0uH FREQ JP4 R M C 0.uF 5 PHMODE ITH RT 4K % SVIN CITH 0pF CFFW 0pF COUT uf 6.V 06 COUT4 uf 6.V 06 SYNC 60 McCarthy Blvd. Milpitas, CA 9505 Phone: (408)4-900 www.linear.com Fax: (408)44-0507 LTC Confidential-For Customer Use Only DUAL SYNCHRONOUS STEP-DOWN REGULATOR LTC6AEFE- DEMO CIRCUIT 896A IC NO. REV. 05/0/ ::05 SHEET OF 8