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Three-channel step-down DC/DC converter touts LDO controller

Posted: 28 Apr 2008 ?? ?Print Version ?Bookmark and Share

Keywords:triple channel? current mode? pulse-width modulation? step-down DC/DC converter? LDO controller?

A triple channel, current mode, pulse-width modulation step-down DC/DC converter with three internal 36V power switches and a low dropout regulator (LDO) controller has been announced by Linear Technology Corp. The LT3507 is packaged in a 38-lead 5mm x 7mm QFN package. One channel is capable of delivering up to 2.4A of output current while the other two switching regulators can deliver 1.5A of continuous output current. Additionally, an integrated LDO controller combined with an external transistor can be connected to VOUT of any of the switching regulators or can be run directly from the input voltage, offering a fourth low noise channel. Its wide input range of 4V to 36V makes it ideal for regulating power from a wide variety of sources from fixed input rails, 24V industrial supplies and automotive batteries. As each switching regulator has its own input pin, up to three different voltage rails can drive the LT3507, offering maximum efficiency for each channel.

Apt for cars
For automotive applications, the LT3507's minimum input voltage of 4V enables it to meet the low input voltage requirements for automotive cold crank conditions. Similarly, its 36V input capability enables it to withstand transients commonly found in load-dump scenarios. The LT3507's 250kHz to 2.5MHz switching frequency is user programmable, enabling it to maximize efficiency while avoiding critical frequency bands such as AM radio bands in automotive applications. Its high frequency operation also enables the use of tiny, low cost inductors and ceramic capacitors, resulting in low, predictable output ripple.

The LT3507's low VCESAT (400mV at 2A and 350mV at 1.5A) internal switches offer efficiencies of up 88 percent, eliminating the need for external heat sinking. All three of the LT3507's converters are synchronized to either a common external clock input or its internal oscillator. The 2.4A channel maintains a 180 phase offset between the two 1.5A channels to reduce input ripple current. An internal 0.80V reference enables sub 1V output voltages required to power the latest generation of low voltage DSPs and MCUs. Independent Run, Tracking/Soft-start and PowerGood indicators ease supply sequencing. Other features include cascadability and user programmable overvoltage and undervoltage lockouts. The low current (The LT3507EUHF is available from stock in a 5mm x 7mm QFN-38. Pricing starts at $4.25 each in 1,000-piece quantities. The LT3507IUHF industrial temperature I-grade (-40C to 125C), version and the LT3507HUHF automotive H-grade (-40C to 150C) version are available from stock. Pricing starts at $5.10 and $5.35 respectively, in 1,000-piece quantities.

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