APPLICATION NOTES REMOTE ON/OFF CONNECTIONS THE CA SERIES FOR • For normal operation, the remote pin should be left open. • • To disable the converter, pull the remote pin below one volt. Typical current from the remote pin is 2mA pulsed. Open circuit voltage is 5V. Input current draw in the disabled mode will vary with input voltage, typically 2mA at low line and 5mA at high line. For more information on the CA Series, refer to page 70. EXTERNAL ADJUSTABLE TRIM FEATURES: CA SERIES SINGLES/TRIPLES • Output voltage accuracy is factory trimmed to within ± 1%. • If the output voltage is trimmed down to below • • approximately 2/3 of Vout, the converter will shut down and cycle on/off (12V and 15V models). Output voltage will trim up approximately 10% by shorting trim to common. Triple Output Modules: Do not trim up by connecting trim to -12, -15 out. This will result in OVP Zener failure. Trimming up will increase overhead voltage on auxiliary regulators and increase internal power dissipation. For more information on the CA Series, refer to page 70. EXTERNAL ADJUSTABLE TRIM FEATURES: CA SERIES DUALS • • Output voltage accuracy is factory trimmed to within ± 1%. • For calculations, Vout is the total voltage between +Out EXTERNAL ADJUSTABLE TRIM FEATURES OF SI/SIW SERIES SINGLES • and -Out. Output voltages will split according to regulation curves. • If the output voltage is trimmed down to below approximately 2/3 of Vout, the converter will shut down and cycle on/off. • Output voltage will trim up approximately 10% by shorting trim to -Out. • For more information on the CA Series, refer to page 70. REMOTE ON/OFF CONNECTIONS THE SI AND SIW SERIES FOR • For normal operation, the remote pin should be left open. • To disable the converter, pull the remote pin below one volt. • Typical current from the remote pin is 2mA pulsed. • Input current draw in the disabled mode will vary with input voltage, typically 2mA at low line and 5mA at high line. • For more information about the SI and SIW Series, refer to pages 56-57 and 62-63. TECHNIQUES FOR OUTPUT RIPPLE/NOISE MEASUREMENT • Output voltage accuracy is factory trimmed to within ± 1%. • If the output voltage is trimmed down to below • • • approximately 60% of Vout, the converter will shut down and cycle on/off (15V and 24V models). Output voltage will trim up approximately 10%, however, do not short trim pin to -Sense pin on 15V and 24V models as this may cause OVP Zener failure. SI and SIW Duals and Triples do not have external trim capabilities. For more information about the SI and SIW Series, refer to pages 56-57 and 62-63 Fusing Notes The DC/DC converter input line should always be fused in order to ensure protection and safety. A fuse rated for 150% to 200% of the DC input current (to the supply at full load) should suf fice. Encapsulated power supplies, in general, do not have internal fuses and an external fuse should be used. Fast blow or slow blow fuses may be verified with the manufacturer. • A 0.1 µ F ceramic capacitor across the probe is recommended to suppress radiated noise pick-up. • When taking ripple/noise measurements, use contact probe tip and ground ring as shown. Using a ground lead will cause false readings. Measurements are taken with output appropriately loaded and all ripple/noise specifications are from D.C. to 20 MHz B.W. 136 603-778-2300 www.wallindustries.com APPLICATION NOTES Heat Generation and Efficiency dissipation and approximately 10% less for a 37.5 watt power dissipation for the 100/150 watt PD and HD Series. All power converters generate heat. The amount of heat generated depends upon the output power used and the efficiency of the power converter. A dissipation of 25 watts corresponds to an 80% efficiency for a 100 watt model while 37.5 watts corresponds to 80% efficiency for a 150 watt model. The addition of forced air to the system will result in lower thermal resistance of the module baseplate. Wall’s PD and HD Series of DC/DC Converters are efficient to 80% or better at full power depending on output voltage. The power not supplied to the output (PDISS) is wasted as heat. This heat must be removed from the converter to prevent damage to semiconductors, capacitors and other heat sensitive components. Methods of Thermal Management Two forms of thermal management include conduction and convection cooling; both relying on the principles of thermal resistance. Simplified, thermal resistance is a measure of the ability of a material to conduct heat. For ideal operation of converters, the lower the thermal resistance - the more improved heat dissipation and transfer will be. Conduction Cooling Methods Figure 1 Required Air Flow (LFM*) Free convection 200 400 600 800 1000 Baseplate Thermal Resistance (°C/Watt) 5.0 2.8 1.8 1.4 1.2 1.0 Required air flow to gain a lower thermal resistance. Thermal Management Using Heatsinks External Finned Heatsinks Through conduction cooling methods, heat is transferred away from the baseplate through an interface material which corrects surface irregularities. One form of this material, commonly known as Kondux, is available in 0.005” sheets; an alternative is thermal grease in the paste form. This material should have a thermal resistance of 0.2°C/Watt maximum. The baseplate temperature can be calculated by multiplying the thermal resistance of the interface material (R Theta i) by the number of watts being dissipated and adding this to the temperature of the surface to which the baseplate is being attached...either chassis or coldplate. Convection Cooling Methods Convection cooling is a process where heat flows from a hotter surface into the surrounding cooler ambient air. The baseplate surface to air thermal resistance is empirically estimated at 5°C/Watt for a 25 watt power The addition of an external finned heatsink to the converter can dramatically lower the thermal resistance, thereby reducing the temperature rise of the converter. The two most common styles of industry standard extrusions offer lengthwise or crosswise fins...either can be used with Wall’s 100 or 150 watt PD or HD Series. A table of thermal resistance for a 0.9” heatsink follows in Figure 2. Crosswise Fin Required Heatsink Airflow (°/Watt) (LFM) 3.00 3.50 1.00 1.79 0.72 1.12 Lengthwise Fin Heatsink (°/Watt) Free Convection 200 400 Thermal Resistance for various external finned heatsinks in 100/150watt units. Wall Industries, Inc. 603-778-2300 137 APPLICATION NOTES Fig. 5: 100 watt converter - Natural Convection EXAMPLE: The maximum output power attainable can be computed by the formula: T max - T ambient R theta sa (1/eff-1 ) = P out max *LFM = Linear Feet per Minute. Note: for figure 4-5, all deratings are based on a 25°C start point with a max baseplate and heatsink temperature of 100°C. Fig. 6 - 150 watt converter - Natural Convection Where R Theta sa is the baseplate, or heatsink resistance (sinked to air), and eff is converter efficiency. From this equation, curves can be derived which will show power derating vs. ambient temperature and heatsink resistance Thermal Chart Examples These curves are based on an assumed 80% efficient converter. 138 603-778-2300 www.wallindustries.com APPLICATION NOTES This application note applies to CA, QAW, SI, SIW, SP and FE model converters. These resistor values apply to CA and FE models, for other values consult factory. Trim Connections and Values Fixed Methods for Trimming Single and Triple Notes on Trim Connections for Converters • Output voltage accuracy is factory-trimmed to within 1% of specified output voltage. • For calculations, Vout is the total voltage between +Vout and -Vout or common. Output voltage will split according to regulation curves. • If the output voltage is trimmed down below approximately 66% of Vout, the converter will shut down and cycle on/off. • Output voltage will trim up approximately 10% Single and Triple Output Converters Fixed Methods for Trimming Single and Triple Triple Output Models • Do not trim by connecting trim pin to -12VDC or -15DVDC output pins, this will result in over-voltage protection Zener failure. • Trimming up will increase overhead voltage on auxiliary regulators and increase internal power dissipation. Internal Circuitry Adjustable Method for trimming Single and Triple Output Converters Up and Down Wall Industries, Inc. 603-778-2300 139 APPLICATION NOTES Dual Output Converters Trim Connections and Values Internal Circuitry Fixed Method for Trimming Dual Converters Up Bottom View (Pin Side) Fixed Method for Trimming Dual Output Converters Down Matrix of Internal Resistor Values Adjustable Method for Trimming Dual Converters Up and Down 140 603-778-2300 www.wallindustries.com