LM2653MTC-ADJ from Texas Instruments
Texas Instruments offers engineers a set of switching regulator evergreens which combine high efficiency with simple PCB layouts. The highly efficient LM2653, first introduced in 1999, usually stands in the shadow of his SimpleSwitch-branded brothers.
While the letter are expensive and don’t deliver high efficiency, the LM2653 performs efficiently and affordably over a wide range of output currents.
The part at hand is efficient at both low and high currents.
From a technical point of view, there is not much to say about the part. It is a switching regulator which boasts a working frequency of 300kHz, and uses a coil and an inductor to perform a bucking operation. An example schematic presents itself like figure two.
Setting up the advanced features requires a set of capacitors and resistors
The relative complexity of the example can be explained by looking at the block diagram. In addition to the thermal and overcurrent protection available in almost all switching regulators, the part contains a set of delay circuits which perform additional safety checks.
Hot feature number one is the soft start capacitor, which usually gets connected to pin SS. The IC charges it with the current of about 2 µA, and watches the voltage level until it reaches 2V. That way, the system starts up slowly, which can be helpful when charging capacitors and other elements.
Secondarily, the system has undervoltage and overvoltage protection. Should the load be able to sink the voltage to less than 80% of the desired value, a delay capacitor is charged slowly but surely – when it reaches a voltage level of 2V, the part switches off the supply to prevent short circuit and similar damages.
From a technical point of view, the part at hand is relatively docile. The datasheet contains detailed information on capacitor and diode selection, and comes with a few precalculated examples. The IC itself is available in TSSOP housing with sixteen pins.