DC1988A Analog Devices

DEMO MANUAL DC1988A LTM8058 Isolated Module DC/DC Converter with LDO Post Regulator Description Demonstration circuit 1988A is a 2kV AC (3kVDC) isolated in the LTM8058 data sheet to determine the minimum load flyback Module DC/DC converter with LDO post regulator current for other input/output configurations. featuring the LTM 8058. The demo circuit is designed for The two-stage converter provides an isolated flyback output a 6V flyback output and a 5V post regulator output from as well as a low noise LDO output. Figure 2 shows the a 4.5V to 30V input. The current capability of the 6V fly- output noise spectrum on V and Figure 3 shows the OUT1 back output varies with input voltage from about 100mA output noise spectrum on V . OUT2 at 4.5V to about 320mA at 30V . Figure 1 shows the IN IN The LTM8058 data sheet gives a complete description typical maximum output current on V when V is OUT1 OUT2 of the device, operation and application information. The not loaded. V is the LDO post regulator from V . OUT2 OUT1 data sheet must be read in conjunction with this quick The current capability of V is limited by either the cur- OUT2 start guide for demo circuit 1988A. rent capability of V minus V loading or the 300mA OUT1 OUT1 current limit on the LDO post regulator itself. R1 provides Design files for this circuit board are available at the necessary minimum load current to keep the V OUT1 DEMO MANUAL DC1988A Quick s p D Demo circuit 1988A is easy to set up to evaluate the per- 0 formance of the LTM8058. Refer to Figure 4 for proper 10 measurement equipment setup and follow the procedure 20 below: 30 40 NOTE. When measuring the input or output voltage ripple, 50 care must be taken to avoid a long ground lead on the 60 oscilloscope probe. Measure the input or output voltage 70 ripple by touching the probe tip directly across the V or IN 80 V and GND terminals. See Figure 5 for proper scope OUT 90 probe technique. 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 FREQUENCY (MHz) 1. With power off, connect the input power supply to V IN dc1988a F02 and GND. Figure 2. V Output Noise Spectrum with I OUT1 OUT1 2. Turn on the power at the input. at 100mA and V at 12V (V Has No Extra Load) IN OUT2 NOTE. Make sure that the input voltage does not exceed 30V. 0 3. Check for the proper output voltages. (For V , check OUT1 10 the voltage between V and V . For V , check OUT1 OUT OUT2 20 the voltage between V and V .) OUT2 OUT 30 NOTE. If there is no output, temporarily disconnect the 40 load to make sure that the load is not set too high. 50 4. Once the proper output voltages are established, adjust 60 the load within the operating range and observe the 70 output voltage regulation, ripple voltage, efficiency and 80 other parameters. 90 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 400 FREQUENCY (MHz) dc1988a F03 350 300 Figure 3. V Output Noise Spectrum with I OUT2 OUT2 at 100mA and V at 12V (V Has No Extra Load) IN OUT1 250 200 150 100 50 0 4 6 8 10 12 14 16 18 20 22 24 26 28 30 V (V) IN dc1988a F01 Figure 1. V Typical Maximum Output OUT1 Current vs V with V Unloaded IN OUT2 dc1988af 2 OUTPUT CURRENT (mA) INTENSITY (dBm) INTENSITY (dBm) ure roce tart