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OKI-78SR Datasheet(PDF) 9 Page - Murata Power Solutions Inc. |
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OKI-78SR Datasheet(HTML) 9 Page - Murata Power Solutions Inc. |
9 / 10 page Soldering Guidelines Murata Power Solutions recommends the specifications below when installing these converters. These specifications vary depending on the solder type. Exceeding these specifica- tions may cause damage to the product. Be cautious when there is high atmospheric humidity. We strongly recommend a mild pre-bake (100 ºC. for 30 minutes). Your production environment may differ therefore please thoroughly review these guidelines with your process engineers. Reflow Solder Operations for surface-mount products (SMT) For Sn/Ag/Cu based solders: For Sn/Pb based solders: Preheat Temperature Less than 1 ºC. per second Preheat Temperature Less than 1 ºC. per second Time over Liquidus 45 to 75 seconds Time over Liquidus 60 to 75 seconds Maximum Peak Temperature 260 ºC. Maximum Peak Temperature 235 ºC. Cooling Rate Less than 3 ºC. per second Cooling Rate Less than 3 ºC. per second Input Fusing Certain applications and/or safety agencies may require fuses at the inputs of power conversion components. Fuses should also be used when there is the possibility of sustained input voltage reversal which is not current-limited. For greatest safety, we recommend a fast blow fuse installed in the ungrounded input supply line. The installer must observe all relevant safety standards and regulations. For safety agency approvals, install the converter in compliance with the end-user safety standard. Input Under-Voltage Shutdown and Start-Up Threshold Under normal start-up conditions, converters will not begin to regulate properly until the rising input voltage exceeds and remains at the Start-Up Threshold Voltage (see Specifications). Once operating, converters will not turn off until the input voltage drops below the Under-Voltage Shutdown Limit. Subsequent restart will not occur until the input voltage rises again above the Start-Up Threshold. This built-in hysteresis prevents any unstable on/off operation at a single input voltage. Users should be aware however of input sources near the Under-Voltage Shutdown whose voltage decays as input current is consumed (such as capacitor inputs), the converter shuts off and then restarts as the external capacitor recharges. Such situations could oscillate. To prevent this, make sure the operating input voltage is well above the UV Shutdown voltage AT ALL TIMES. Start-Up Time Assuming that the output current is set at the rated maximum, the Vin to Vout Start-Up Time (see Specifications) is the time interval between the point when the rising input voltage crosses the Start-Up Threshold and the fully loaded regulated output voltage enters and remains within its specified regulation band. Actual measured times will vary with input source impedance, external input capacitance, input voltage slew rate and final value of the input voltage as it appears at the converter. These converters include a soft start circuit to moderate the duty cycle of its PWM controller at power up, thereby limiting the input inrush current. Recommended Input Filtering The user must assure that the input source has low AC impedance to provide dynamic stability and that the input supply has little or no inductive content, including long distributed wiring to a remote power supply. The converter will operate with no additional external capacitance if these conditions are met. APPLICATION NOTES For best performance, we recommend installing a low-ESR capacitor immediately adjacent to the converter’s input terminals. The capacitor should be a ceramic type such as the Murata GRM32 series or a polymer type. Initial suggested capacitor values are 10 to 22 μF, rated at twice the expected maxi- mum input voltage. Make sure that the input terminals do not go below the undervoltage shutdown voltage at all times. More input bulk capacitance may be added in parallel (either electrolytic or tantalum) if needed. Recommended Output Filtering The converter will achieve its rated output ripple and noise with no additional external capacitor. However, the user may install more external output capaci- tance to reduce the ripple even further or for improved dynamic response. Again, use low-ESR ceramic (Murata GRM32 series) or polymer capacitors. Initial values of 10 to 47 μF may be tried, either single or multiple capacitors in parallel. Mount these close to the converter. Measure the output ripple under your load conditions. Use only as much capacitance as required to achieve your ripple and noise objectives. Excessive capacitance can make step load recovery sluggish or possibly introduce instability. Do not exceed the maximum rated output capaci- tance listed in the specifications. Input Ripple Current and Output Noise All models in this converter series are tested and specified for input reflected ripple current and output noise using designated external input/output compo- nents, circuits and layout as shown in the figures below. The Cbus and Lbus components simulate a typical DC voltage bus. Please note that the values of Cin, Lbus and Cbus will vary according to the specific converter model. CIN VIN CBUS LBUS CIN = 2 x 100μF, ESR < 700mΩ @ 100kHz CBUS = 1000μF, ESR < 100mΩ @ 100kHz LBUS = 1μH +INPUT -INPUT CURRENT PROBE TO OSCILLOSCOPE + – + – Figure 2: Measuring Input Ripple Current OKI-78SR Series Fixed Output 1.5 Amp SIP DC/DC Converters www.murata-ps.com email: sales@murata-ps.com PRELIMINARY 22 Mar 2010 MDC_OKI-78SR-W36.A01_D6 Page 9 of 10 |
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