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.

+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