dn441 pdf

Typical industrial and automotive applications require
multiple high current, low voltage power supplies to
drive everything from disk drives to microprocessors.
The LT?3507 triple step-down converter ? ts easily into
these applications. It is simple and compact compared
to multi-chip solutions.
The LT3507 is a single IC current mode triple step-
down regulator with internal power switches and a low
dropout linear regulator driver. The switching convert-
ers are capable of generating one 2.4A output and two
1.5A outputs. All three converters are synchronized to a
single oscillator, with the 2.4A output running antiphase
to the other two converters, thereby reducing input ripple
current. Each converter has independent shutdown and
soft-start circuits and generates a power good signal
when its output is in regulation, simplifying both supply
sequencing and the interface with microcontrollers and
DSPs. Separate input pins for each regulator offer ad-
ditional ? exibility; regulators can be cascaded to reduce
circuit size, or each regulator can draw power from a
different input source.
The switching frequency is set with a single resistor
between 250kHz to 2.5MHz. High switching frequency
allows the use of small inductors and capacitors result-
ing in a very compact triple output supply. The constant
switching frequency, combined with low impedance
ceramic capacitors, results in low output ripple. With
its wide input voltage range of 4V to 36V, the LT3507
regulates a broad array of power sources including 5V
logic rails, unregulated wall transformers, lead acid bat-
teries and distributed power supplies.