DC518A Analog Devices

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 518 SLIC POSITIVE INPUT TO NEGATIVE OUTPUT DC/DC CONVERTER LTC3704 DESCRIPTION Demonstration circuit 518 is a positive input to circuit features an optional soft-start circuit that can negative output SLIC (Subscriber Line Interface be enabled or disabled with a single jumper. Circuit) converter featuring the LTC3704 switch- DC518 has a jumper to program either continuous ing controller. DC518 converts 4.5V to 15V input or Burst-Mode operation and can be synchronized to 24V and 70V output and provides over to an external clock of up to 400kHz. Please refer 200mA of output current from a 5V input. The to the LTC3704 data sheet for design details and converter operates at 200kHz with high efficiency applications information. of up to 92%. The DC518 is set to operate with current sense resistor RS1 and input voltages up The DC518 can produce up to 200mA at both out- to 15V. However, DC518 can be modified for No- puts from a 5V input source. TM Rsense operation with a 5V input voltage, pro- vided that MOSFET drain voltage does not exceed Design files for this circuit board are available. Call the LTC factory. 36V (main output set between 0V and -24V). The Table 1. Performance Summary PARAMETER CONDITION VALUE Minimum Input Voltage 4.5V Maximum Input Voltage 15V V V = 5V to 15V, I = 0A to 0.2A -24V 3% OUT1 IN OUT1 V V = 5V to 15V, I = 0A to 0.2A -70V 10% OUT2 IN OUT2 Typical Output Ripple V V = 5V to 15V, I = 0A to 0.2A 200mV OUT1 IN OUT1 PP Typical Output Ripple V V = 5V to 15V, I = 0A to 0.2A 500mV OUT2 IN OUT2 PP Nominal Switching Frequency 200kHz QUICK START PROCEDURE Demonstration circuit 518 is easy to set up to 1. Place jumper JP1 in the Vin position. The Pre evaluate the performance of the LTC3704. Refer to Reg position is an optional bias source for appli- Figure 1 for proper measurement equipment setup cations modified for Vin higher than 36V. A bias and follow the procedure below: circuit including Q4 and D5 is installed on the board in order to facilitate modifications for higher NOTE: When measuring the input or output volt- Vin. age ripple, care must be taken to avoid a long ground lead on the oscilloscope probe. Measure 2. With power off, connect the input power supply to the input or output voltage ripple by touching the Vin and GND. Make sure that the input power sup- probe tip directly across the Vin or Vout and GND ply has sufficient current rating at minimum input terminals. See Figure 2 for proper scope probe voltage for the required output load. technique. 3. Turn on the power at the input. 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 518 SLIC POSITIVE INPUT TO NEGATIVE OUTPUT DC/DC CONVERTER NOTE: Make sure that the input voltage does not 5. Once the proper output voltage is established, exceed 15V. adjust the load within the operating range and ob- serve the output voltage regulation, ripple voltage, 4. Check for the proper output voltages. V = -24V OUT1 efficiency and other parameter and V = -70V OUT2 If there is no output, temporarily disconnect the load to make sure that the load is not set too high. Figure 2. Scope Probe Placement for Figure 1. Proper Measurement Equipment Setup Measuring Input or Output Ripple 2