LINEAR dn403f Data Sheet

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A Compact Dual Step-Down Converter with VOUT Tracking and Sequencing – Design Note 403 Tiger Zhou and David Canny Introduction • A 180° phase relationship between the channels is

Typical industrial and automotive applications require maintained to reduce input voltage ripple and input multiple high current, low voltage power supply solutions capacitor size.

to drive everything from disc drives to microproces-

• Independent input voltage, feedback, soft-start and

sors. For many of these applications, particularly those

power good functions for each converter simplify the

that have size constraints, the LT3501® dual step-down

implementation of all the tracking and sequencing

converter is an attractive solution because it’s compact

options available.

and inexpensive compared to a 2-chip solution. The dual

converter accommodates a 3V to 25V input voltage range • Minimum input-to-output voltage ratios are extended and is capable of supplying up to 3A per channel. The by allowing the switch to stay on through multiple circuit in Figure 1 produces 3.3V and 1.8V. clock cycles resulting in a 95% maximum duty cycle regardless of switching frequency.

LT3501 Dual Converter Features

• The LT3501 automatically resets the soft-start function

• The LT3501 is feature-rich and comes with internal 3.5A

if the output drops out of regulation so that a short

switches and sense resistors to minimize solution size

circuit or brownout event is graceful and controlled.

and cost.

• One or both converters can be shutdown at any time

• The LT3501 operates at a fi xed frequency between

if they’re not being used, reducing input power drain.

250k Hz and 1.5MHz, programmed using a single re- sistor or synchronized to an external clock, allowing • The LT3501 is available in a 20-pin TSSOP package optimization of effi ciency and solution size. with an exposed pad for low thermal resistance.

, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners.

VIN 4.5V TO 24V

X5R (f SW = 500k Hz)

VIN1 VIN2

SHDN RT/SYNC

BST1 BST2

SW1 SW2

LT3501

PMEG4005PMEG4005

VOUT1 IND1 IND2 VOUT2

VOUT1 VOUT2

3A, VIN < 16V 3A, VIN < 16V 2.8A, VIN > 16V* 100k 100k 2.8A, VIN > 16V*

PG1 PG2 FB1 FB2 VC1 VC2 SS/TRACK1 SS/TRACK2

8.06k 40.2k GND 40.2k 8.06k

DN403 F01

*FOR 3A CAPABILITY ABOVE 16V, INCREASE INDUCTOR VALUE BY 33%.

Figure 1. Compact Dual 3A Step-Down Converter with Ceramic Capacitors