* Apple accounts for up to half of Dialog's revenue - analysts
* Dialog shares tumble by more than 20 pct
* Anglo-German chipmaker says no change in business relationships
* Apple suppliers' shares, iPhone launches: http://bit.ly/2wWjy0T (Adds analyst comments, Dialog Semi share price performance)
FRANKFURT, Nov 30 (Reuters) - Apple is designing its own power-management chips for use in iPhones as early as 2018, the Nikkei business daily reported on Thursday, triggering a more than 20 percent slide in shares of supplier Dialog Semiconductor.
If confirmed, the move would reduce Apple's dependence on the Anglo-German chipmaker, which itself is heavily reliant on the smartphone industry and has been trying to diversify its customer base.
By 1526 GMT Dialog shares were still down a shade more than 19 percent at 30 euros.
Investors are particularly jittery after Apple said in April that it planned to replace graphics chip supplier Imagination Technologies, sending the London-listed stock down 70 percent in a single session. Imagination was subsequently sold off in two separate deals.
In the past dozen years U.S. tech giant Apple has dropped several smaller chip suppliers, ultimately forcing them to merge with bigger rivals.
Responding to the Nikkei report, which quoted unnamed sources, a Dialog spokesman said its business situation had not changed.
"The level of visibility into the design cycle of our leading customers remains unchanged and the business relationships are in line with the normal course of business," the spokesman said.
Apple did not immediately respond to a request for comment.
The sell-off echoed one in April, after Bankhaus Lampe analyst Karsten Iltgen advised investors to sell Dialog shares because Apple was working on its own battery-saving chip to replace Dialog's power-management integrated circuits, or PMICs.
Asked to comment on the Nikkei report, Iltgen said: "I don't know their sources, but our own checks always suggested that this is an 'open secret' in the industry.
"Therefore, we are not surprised that finally another source is verifying our thesis. The article is certainly credible, in our view."
DIALOG'S LOSS, TSMC'S GAIN
The Nikkei business daily quoted one source saying iPhone would make about half its own power-management chips, starting next year, with another source saying this could be delayed until 2019. (http://s.nikkei.com/2Al5nSl)
The Apple-designed chips would be solely manufactured by Taiwan Semiconductor Manufacturing Co (TSMC), according to industry sources cited by the newspaper.
TSMC, the world's biggest contract chipmaker, has been Apple's sole supplier of core processor chips for iPhones since 2016 and also makes Dialog's power-management chips.
Dialog Semiconductor shares have lost 36 percent of their value since the April sell-off, reducing the company's market capitalisation to 2.74 billion euros ($3.27 billion), according to Reuters calculations.
Company management typically does not comment on individual customers and has been guarded in its statements about the likely impact of Apple's launch of the iPhone X, its tenth anniversary model.
Speaking to investors in mid-November, Chief Executive Jalal Bagherli said Dialog stood to benefit from up to six or seven new growth drivers that represented efforts to diversify but refused to be drawn on any possible Apple boom.
Dialog derives more than half of its revenue from Apple, analysts estimate. Two years ago close to three quarters of its revenue came from being sole supplier of power-management chips for use in Apple devices. ($1 = 0.8386 euros)
(Additional reporting by Eric Auchard and Paul Sandle in London and Aishwarya Venugopal in Bengaluru; Editing by Shounak Dasgupta and David Goodman)