DEMO MANUAL DC1997A-A/DC1997A-B LTC3838EUHF-1/ LTC3838EUHF-2 High Current, Dual Output Synchronous Buck Converter DESCRIPTION Demonstration circuits DC1997A-A/DC1997A-B are The entire converter, excluding the bulk input and output 2 dual output synchronous buck converters featuring the capacitors, fits within a 1.5in area on the board. The high LTC 3838EUHF-1/LTC3838EUHF-2. Both assemblies density is a result of the compact, 2-sided drop-in layout provide two outputs of 1.5V/20A and 1.2V/20A over an and the use of dual channel FETs. input voltage range of 4.5V to 14V at a switching frequency Additional features of this demo board include: of 300kHz. Remote sensing for each output. Applications requiring the output to be adjusted with an PLLIN and CLKOUT pins. external reference can be implemented with the DC1997A-B assembly. Such applications include adaptive voltage scal- PGOOD, RUN and TRK/SS pins for each output. ing optimization (AVSO) where the processor voltage is Optional resistors to tie the two outputs together. adjusted to achieve optimal efficiency, wide output voltage applications controlled by a DAC, or margining. The 2nd Optional footprint for discrete single channel FETs for channel of the DC1997A-B assembly is regulated to an higher output current. onboard 1.2V reference in the default setup. The same Optional footprints to implement DTR (detect transient) reference can be set from 0.8V to 1.5V with a potentiometer to reduce overshoot following a load release. or the 2nd channel can regulate to a source external to the board. The 1st channel on the DC1997A-B assembly and Design files for this circuit board are available at both channels on the DC1997A-A version are regulated DEMO MANUAL DC1997A-A/DC1997A-B QUICK START PROCEDURE Demonstration circuit DC1997A-A/DC1997A-B is easy to Adjusting the Onboard Reference: set up to evaluate the performance of the LTC3838EUHF-1/ 1. Remove power from the input of the board. LTC3838EUHF-2. Please refer to Figure 1 for proper mea- 2. Place these jumpers in the following positions: surement equipment setup and follow the procedure below. JP5 ON BD REF ADJ 1. With power off, connect the input supply, load and meters as shown in Figure 1. Preset the load to 0A JP6 REF ON BD and VIN supply to be 0V. For both assemblies, place 3. Apply power to the input of the board. the jumpers in the following positions: 4. Adjust reference with potentiometer at R52. JP4 RUN1 ON Connecting a Reference External to the Board: JP1 RUN2 ON 1. Remove power from the input of the board. JP2 MODE FCM 2. Place JP6 in the EXT position. The DC1997A-B assembly has additional jumpers for the reference circuit. Place these jumpers in the following 3. Connect the external reference between the EXTREF2+ positions: and EXTREF2- turrets. JP5 ON BD REF FIXED 4. Apply power to the input of the board. JP6 REF ON BD 5. Turn-on the external reference. 2. Adjust the input voltage to be between 4.5V and 14V. Note 3: For accurate efficiency measurements in DCM at V should be 1.5V 2%. OUT1 light load at V greater than 5V, remove R51 and apply IN V should be 1.2V 2%. OUT2 an external reference to the board as mentioned above. 3. Next, apply 20A load to each output and re-measure Single Output/Dual Phase Operation V . OUT A single output/dual phase converter may be preferred 4. Once the DC regulation is confirmed, observe the output for higher output current applications. The optional com- voltage ripple, load step response, efficiency and other ponents required to tie the phases together are found on parameters. the top middle of the first sheet. To tie the two outputs Note 1: Use the BNC connectors labeled V or V OUT1 OUT2 together, make the following modifications: to measure the output volt-age ripple. 1. Tie the two VOUT shapes together with a piece of copper Note 2: Do not connect load from the VO1 SNS+ turret at the edge of the board where the copper is exposed. to the VO1 SNS- turret or from the VO2 SNS+ turret to 2. Tie the VOUT SENSE1+ pin to INTVCC with a 0 jumper the VO2 SNS- turret. This could damage the converter. at R8. This will tie ITH1 to ITH2 inside the chip. Only apply load across the stud connectors on the edge of the board. 3. Tie RUN1 to RUN2 by stuffing a 0 jumper at R15. 4. If DTR is implemented, then stuff 0 jumper at R9 to Reference Circuit for Channel 2 of DC1997A-B tie the two DTR pins together. Assembly Channel 2 of the DC1997A-B assembly is configured by default to regulate to the fixed 1.2V reference generated by the LT 6650 reference circuit. If desired, this reference can be set with a potentiometer, or an external source such as a DAC or another source. See the following instructions to set the board for either: dc1997a-af 2