New-Tech Europe | December 2016 | Didital Edition

components need to carefully chosen and their operation modeled, which even using the design tools many vendors offer is still time-consuming. Far better, especially for system designers who are not power experts, is to use power modules that integrate the PWM controller, MOSFET power switches and inductor in a single small form-factor package. These modules are typically designed, optimized and tested by a multi-disciplinary team of engineers who are each experts in their own field. Consequently this provides the application design engineer with a device that delivers superior performance, high reliability and the benefit of immediate availability, cutting down the time to market by several months. Good examples of these devices are the latest members of Exar’s expanding family of modules; the XR79103/06 and XR79203/06 deliver 3A and 6A outputs at voltages down to 0.6V from input supplies of up to 22V and 40V respectively. What do these modules offer? Implemented as synchronous step- down buck converters, these power modules employ a proprietary emulated current-mode Constant On- Time (COT) control loop. They require no external loop compensation and are unconditionally stable using ceramic output capacitors and operate at near-constant switching frequency, requiring very few external housekeeping components. The wide input voltage range allows the XR79103/06 to operate from industry standard 5V, 12V and 19.6V rails while the XR79203/06 can cope with standard 24V and 18-36V DC rails, and also rectified 18VAC and 24VAC rails. Consequently these modules not only fulfill the earlier wish list, which

Figure 3. Thermal derating curve for Exar’s XR79106 power module at VIN = 12V

Figure 4. Power modules require just a few external housekeeping components and full details of how to calculate the values of these are provided in the datasheet

but is trumped by a module

amplifier and the ramp generator and comparator, which form the pulse-width modulator that controls the power switch. However this still leaves the MOSFET, LC output filter and most of the passive compensation feedback components off-chip. These

Today semiconductor companies provide DC-DC converter solutions that integrate many of the control elements of a switching regulator, such as the compensation many

New-Tech Magazine Europe l 23