* Q4 operating income down 22 pct yr-on-yr
* Q-on-Q slowdown in sales, expected to persist in Q4
* Automotive unit drags
* Forecasts 9 pct revenue growth in fiscal 2018 (Adds details on microchips for cars, quarterly performance)
FRANKFURT/MUNICH, Nov 14 (Reuters) - German chipmaker Infineon, the top supplier of power controls to auto and industrial markets, on Tuesday reported a slowdown in sequential sales due to a weaker dollar.
Infineon reported fourth-quarter operating income of 177 million euros ($207 million), a year-on-year decline of 22 percent, below average expectations of 281 million euros in a Reuters poll of analysts.
Revenues rose 9 percent from a year earlier to 1.82 billion euros but were down 1 percent from the previous quarter. The consensus forecast was for 1.838 billion euros, according to 15 analysts polled by Reuters.
"Infineon continues to grow. We raised the outlook for the full fiscal year in March 2017 and achieved the higher targets, despite stronger headwinds caused by the weaker U.S. dollar," CEO Reinhard Ploss said in a statement.
Infineon shares were indicated 2.6 percent lower in pre-market trading by broker Lang & Schwarz.
At Monday's close, the stock was up 42 percent in the current year to date, beating a 22 percent gain in the Stoxx European Tech Index.
Last year, eight out of 10 of the world's top selling battery or plug-in electric vehicles were powered by Infineon chips, according to the company.
Infineon is the top maker of microcontrollers used in the central powertrains of many luxury vehicles, although it lags Renesas, NXP and Texas Instruments in the wider market for car microcontrollers.
Weakness in the fourth quarter of Infineon's fiscal year to Sept. 30 was concentrated in the automotive division, where revenues declined by 4 percent on a quarter-on-quarter basis to 736 million euros.
Infineon said it expected a seasonally typical slowdown in sales of 2 percent in the current quarter, within a range of 2 percentage points either way, and a segment result margin of 15 percent.
The company reported a fourth-quarter segment result - which captures the operating performance excluding certain items - of 328 million euros, up 17 percent, and a margin of 18 percent. ($1 = 0.8570 euros) (Reporting by Irene Preisinger and Douglas Busvine; Editing by Ludwig Burger and Louise Heavens)