Electronic Design

Power Converter Stands Out From The POL Crowd

SIP-style nonisolated dc-dc converter offers surface-mount assembly, a wide input-voltage range, and programmable output voltage.

Point-of-load (POL) dc-dc converters are commonly offered in single inline packages (SIPs), which are valued for their ability to save board space and enhance cooling. Unfortunately in some applications, these SIPs may be the only through-hole components on the pc board. As a result, they must be assembled separately from the other surface-mount parts. A new nonisolated POL dc-dc converter crafted by Power-One remedies this problem with a surface-mountable SIP.

The Y5117P, a 17-A POL dc-dc converter, can be assembled to the board using standard pick-and-place equipment thanks to its use of specially designed interconnects as well as to its small size and weight. The SIP measures just 0.314 by 1.26 by 0.55 in. (8 by 32 by 14 mm) and weighs only 5.2 g—well within the limits of common pick-and-place apparatus (see the figure). The device can be handled by either vacuum-style pick-and-place equipment or mechanical grippers.

Beyond its compatibility with surface-mount assembly, the Y5117P also boasts an uncommonly wide input-voltage range, a programmable output voltage, and high current density. The input- and output-voltage capabilities permit the use of a single POL converter in a range of applications, relaxing the required stocking of different models.

The Y5117P accepts inputs ranging from 3 to 13.2 V. In contrast, most POLs are specified for operation from fixed voltages such as 3.3, 5, or 12 V. Typically, most POLs have input-voltage ranges just ±10% of nominal. The wide input-voltage range on the Y5117P enables a single POL to operate off of the three common supply voltages. Moreover, the wide range gives system designers the flexibility of operating from a nonstandard voltage such as 8 V, which may be desirable in distributed power applications that employ an intermediate voltage bus.

Output voltage may be programmed with a single external resistor for voltages ranging from 0.7 to 3.6 V. Again, the ability to cover a range of voltages sets the Y5117P apart from existing models because most specify a fixed output voltage. Although many offer an output trim option, the trim range is generally on the order of ±10%.

Power-One's POL produces a small footprint on the board, just 0.314 by 1.26 in. (8 by 32 mm), which results in a current density of 43 A/in.2 In contrast, other competitive SIP-style POLs with roughly the same output capability (15 to 20 A) achieve current densities in the range of 20 to 40 A/in.2

The efficiency of the POL over its input-voltage range and over load is typically greater than 90%. In terms of performance over temperature, the unit is specified for operation at ambients of −40°C to 110°C with limited airflow (see the online figure). At rated full-load operation, junction temperatures will not exceed 125°C.

Vertical mounting of a SIP package eases thermal management. The converter gets greater exposure to airflow than a similar unit that's horizontally mounted. The end result of this benefit will be reflected in the POL's performance over temperature under different rates of forced-air cooling. With just a modest airflow of 200 LFM, the Y5117P will deliver its rated power at ambients of up to 50°C.

Power-One had to overcome a few key challenges to develop a surface-mountable SIP. One was the need to maintain good coplanarity among the POL's 25 pins. Another was the need to achieve good electrical and thermal contacts between the POL and the pc board on which it is mounted. The unique pinout of the Y5117P reflects the mechanical design that was necessary to fulfill these objectives. Naturally, that pinout precludes compatibility with existing POLs.

Additionally, the POL provides an output-voltage accuracy of ±1%, a maximum ripple and noise output of 50 mV p-p, and a maximum turn-on time of 40 ms. Switching frequency is nominally 510 kHz. Other features include stable no-load operation, current sense, current-limit adjustment, and remote on/off enable. The converter also offers output short-circuit protection and overtemperature protection.

The Y5117P will be available in sample and production quantities in the third quarter. In lots of 1000, unit pricing is $27.


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