DEV Community

ChipApex
ChipApex

Posted on

Notes on the Infineon 111-3013: a 400 kHz buck/boost controller in 8-SOIC

#electronics #hardware

The Infineon 111-3013 is a single-output DC-DC switching controller in an 8-SOIC. It drives an external power transistor and can run either buck or boost with a positive output. The notes below are the parameters I check before keeping a part like this on a repair BOM or a small new board.

What the listing actually specifies

Function is step-up and step-down. Topology is buck and boost, one output, one phase. Output type is a transistor driver. Synchronous rectification is supported. Clock sync is not. The control features called out are Enable and Soft Start. There is no serial interface.

Supply (VCC/VDD) is 4.2 V to 25 V. Switching frequency is 400 kHz. Maximum duty cycle is 90%. Operating temperature is 0 °C to 70 °C ambient, so this is a commercial-range part. Mounting is surface mount. The package is 8-SOIC, 0.154 in (3.90 mm) body width, supplier device package 8-SOIC, shipped in tube. The short description on the manufacturer line is IC REG CTRLR BUCK/BOOST 8SOIC.

The parameter table I used is the one on the Infineon 111-3013 buck/boost controller page. Treat that table as a starting point and confirm pinout, gate-drive voltage, and current limits in the datasheet before layout.

Design notes

400 kHz keeps the inductor and the output capacitors smaller than a 100 kHz design, but gate-drive loss on the external FET is not free. If the FET is picked for a very low Rds(on), its gate charge may be large. At 400 kHz that charge is switched every cycle. Check Qg against whatever drive the controller can actually source and sink. The short description does not state the drive current.

The 90% duty-cycle cap matters more in boost than in buck. A buck from 12 V to 5 V is nowhere near 90%. A boost from a sagging 4.2 V input toward a much higher rail can hit the limit, and Vout will then fall with Vin. Do the Vout/Vin math, including diode or sync-FET drops, before locking the topology.

Synchronous rectification is listed as yes. That usually means a second gate drive for a sync FET instead of a diode. Dead time and the high-side or low-side arrangement are not in the short spec. Scope the switch node on the first prototype and look for shoot-through before you trust an efficiency number from a spreadsheet.

Enable plus soft start is the useful pair for sequencing. Soft start limits inrush into a large output capacitor. There is no clock-sync input, so two of these controllers on one board will free-run. If you need to avoid a beat frequency between two nearby switchers, this is the wrong part.

The ambient rating stops at 70 °C. A sealed enclosure that runs hotter than that needs a wider-temperature controller, or a measurement of the real board temperature with a plan to derate. Catalog TA is not the temperature at the switch node.

Public records list 111-3013 as obsolete. An 8-SOIC footprint match is not a second-source plan. For a new design I would treat this as a legacy or repair item and pick a current buck or boost controller with a stated lifetime. For a board that already uses it, the 8-SOIC is straightforward to rework, but do not assume pinout from the function string. Buck and boost controllers in the same package do not share a pinout.

What I would check on the bench

  1. Confirm VCC stays inside 4.2 V to 25 V through startup and through input steps, including a source that is still rising.
  2. Measure the switch-node frequency. It should sit near 400 kHz. The short spec does not mention spread-spectrum or a burst mode.
  3. At minimum input and maximum load, watch the duty cycle. If it sits on the 90% rail and the output sags, the conversion ratio is the problem, not only the feedback divider.
  4. Capture the soft-start ramp into the real output capacitance, not into an electronic load set to a light constant current.
  5. If a sync FET is fitted, look at both gate drives and the switch node together before you call the design quiet.

Series, grade, and qualification are blank on the listing. Do not read those blanks as "industrial" or "AEC-Q". They are unspecified.

Further reading

Top comments (0)