The highest temperatures in LSM D3 SMT's occur at their output inductor,

developed using thermocouples to monitor the inductor temperature and

varying the load to keep that temperature below +110°C under the assorted

conditions of air flow and air temperature. Once the temperature exceeds

+115°C (approx.), the thermal protection will disable the converter. Automatic

restart occurs after the temperature has dropped below +110°C.

As you may deduce from the derating curves and observe in the efficiency

curves on the following pages, LSM D3 SMT's are more efficient at lower

lower current levels. Consequently, LSN-D3 SMT's deliver very impressive

temperature performance if operating at less than full load.

Lastly, when LSM D3 SMT's are installed in system boards, they are obvi-

ously subject to numerous factors and tolerances not taken into account here.

If you are attempting to extract the most current out of these units under

demanding temperature conditions, we advise you to monitor the output-

inductor temperature to ensure it remains below +110°C at all times.

Output Reverse Conduction

Many DC/DC's using synchronous rectification suffer from Output Reverse

Conduction. If those devices have a voltage applied across their output before

a voltage is applied to their input (this typically occurs when another power

supply starts before them in a power-sequenced application), they will either

fail to start or self destruct. In both cases, the cause is the "freewheeling" or

"catch" FET biasing itself on and effectively becoming a short circuit.

LSM D3 SMT DC/DC converters do not suffer from Output Reverse Conduc-

tion. They employ proprietary gate drive circuitry that makes them immune

to applied output voltages.

Thermal Considerations and Thermal Protection

The typical output-current thermal-derating curves shown below enable

designers to determine how much current they can reliably derive from each

model of the LSM D3 SMT's under known ambient-temperature and air-flow

conditions. Similarly, the curves indicate how much air flow is required to

reliably deliver a specific output current at known temperatures.

Figure 7. Trim Connections Using Fixed Resistors

Figure 6. Trim Connections Using a Trimpot

Trim Equations

Note: Resistor values are in k . Accuracy of adjustment is subject to

tolerances of resistors and factory-adjusted, initial output accuracy.

Note: LSM-0.8/10-D3 is not trimmable.

UP

1.296

DOWN

(k ) =

–

1

–

1

UP

1.992

DOWN

(k ) =

–

2.37

–

2.37

UP

1.896

DOWN

(k ) =

–

4.99

–

4.99

LSM-1/10-D3

Model

LSM-1.2/10-D3

LSM-1.5/10-D3

LSM-1.8/10-D3

LSM-2/10-D3

LSM-2.5/10-D3

Trim Equations

Note:

Install either a fixed

trim-up resistor

or a fixed trim-down

resistor depending upon

desired output voltage.

LSM-10A D3 Models

10 Amp DC/DC’s in SMT Packages

www.murata-ps.com

MDC_LSM-10A D3.B01 Page 6 of 13