DC1801A-B Analog Devices

DEMO MANUAL DC1801A LTC3838EUHF High Efficiency Dual Output Step-Down DC/DC Converter DESCRIPTION Demonstration circuit 1801A is a dual output 1.5V/20A and The main features of the board are listed below: 1.2V/20A synchronous buck converter operating with a MODE jumper to program either discontinuous mode switching frequency of 300kHz over an input voltage range (DCM) or forced continuous mode (FCM) at light or no of 4.5V to 14V. The demo board comes in two versions. load. The A version uses inductor DCR current sensing for high EXTVCC pin. efficiency. The B version uses 2m sense resistor for ac- curate current sensing with a low DCR ferrite inductor. The PLLIN pin to synchronize the converter to an external fixed on-time valley current mode topology of the LTC3838 clock. allows for a fast load step response (see Figures 6 to 9). Remote sensing for V . OUT1 The load step response can be tested with the onboard load step circuit and a bench pulse generator. Optional resistors to tie the two phases together. The demo board uses a high density, two sided drop in Each rail has its own RUN pin, PGOOD pin and layout. The entire converter, excluding the bulk output and TRACK/SS pin. input capacitors, fits within a compact 1.5 1.0 area Design files for this circuit board are available at on the board. The package style for the LTC3838EUHF is DEMO MANUAL DC1801A QUICK START PROCEDURE Demonstration circuit 1801A is easy to set up to evalu- tor the voltage across COUT1 and COUT5 respectively. ate the performance of the LTC3838EUHF. Please refer to Heavy load currents applied across these turrets may Figure 1 for proper measurement equipment setup and damage the converter. follow the procedure below. LOAD STEP TRANSIENT TESTING 1) With power off, connect the input supply, load and meters as shown in Figure 1. Preset the load to 0A Demonstration circuit 1801A provides a simple load step and V supply to be 0V. Place jumpers in the following IN circuit consisting of a MOSFET and sense resistor for each positions: rail. To apply a load step, follow the steps below. JP4 RUN1 ON 1) Preset the amplitude of a pulse generator to 0.0V and the duty cycle to 5% or less. JP1 RUN2 ON 2) Connect the scope to the VOUT BNC connectors for JP3 MODE FCM the rail under test with a coax cable. To monitor the 2) Adjust the input voltage to be between 4.5V to 14V. load step current, connect the scope probe across the V should 1.2V 2%. +/ OUT1 IOSTEP turrets for that rail. V should 1.5V 2%. OUT2 3) Connect the output of the pulse generator to the PULSE 3) Next, apply 20A load and recheck V . GEN turret for the rail under test and connect the return OUT to one of the GND turrets. 4) Once the DC regulation is confirmed, observe the output voltage ripple, load step response, efficiency and other 4) With the converter running, slowly increase the ampli- parameters. tude of the pulse generator output to provide the desired load step pulse height. The scaling for the LOAD STEP Note 1. Use the BNC connectors labeled V or V OUT1 OUT2 signal is 10mV/Amp. to measure the output voltage ripple. + Note 2. Do not apply the load from the VO1 SNS turret + to the VO1 SNS turret or from the VO2 turret to the VO2 turret. These turrets are only intended to moni- dc1801af 2