LINEAR dn404f Data Sheet

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Dual Monolithic Step-Down Switching Regulator Provides 1.6A Outputs with Reduced EMI and VOUT as Low as 0.8V Design Note 404 Hua (Walker) Bai Introduction the LT3506 and the LT3506A have 0.8V high accuracy

Electronic devices are becoming smaller while the power voltage references.

requirements are increasing to satisfy ever more func-

Typical LT3506A and LT3506 Applications

tionality. To preserve power and manage heat, switching

The primary difference between the LT3506A and the

regulators are desirable because of their high effi ciency

LT3506 is the switching frequency. The LT3506A’s switch-

compared to linear regulators.

ing frequency is 1.1MHz while the LT3506’s is 575k Hz.

The LT3506 and the LT3506A are examples of how to Higher switching frequency allows smaller components. squeeze power out of a supply without overheating the For lower output voltages, i.e., less than 3.3V, the LT3506 end product. These are dual 1.6A step-down monolithic is recommended if VOUT/VIN(MAX) is less than 15%. The

EF FI CI EN CY

regulators that simplify the lives of system engineers. They lower switching frequency option usually results in higher eliminate the need for external power switches, thereby effi ciency due to the lower switching and inductor core reducing solution size and BOM cost. Their outputs can losses. be as low as 0.8V, satisfying the needs of the latest DSPs.

The circuit in Figure 1 generates a 3.3V and a 5V output.

Integrated dual output channels reduce the part count,

The overall effi ciency of the circuit (both channels) is

while anti-phase switching of the two channels maximizes

shown in Figure 2. The circuit shown in Figure 3 gener-

effi ciency and reduces input current ripple and EMI. Both

ates a 1.2V and a 1.8V from a 3.6V to 21V input. The wide

4.7µH CDRH4D22/HP-4R7 input voltage of both the LT3506 and the LT3506A (3.6V

VOUT1 5V

NSR0230M2T5G 22µF to 25V) can accept a variety of power sources, from lead-

AT 1.6A

52.3k 10V 10k X5R acid batteries and 5V rails to unregulated wall adapters

U1 and distributed power supplies.

0.1µF LT3506AEDHD

, LT, LTC, LTM are registered trademarks of Linear Technology

FB1 100k

DFLS230L 220p F Corporation. All other trademarks are the property of their respective owners.BOOST1 39k

SW1 VC1

VIN1 PG1 PG1

VIN 6.8V

VIN1 RUN/SS1 RUN/SS1

TO 25V 4.7µF

VIN2 RUN/SS2 RUN/SS2

X5R 6.8V INPUT

VIN2 PG2 PG2

DFLS230L 220p F 28k

SW2 VC2

12V INPUT

BOOST2 FB2 GND

DN404 F01 100k

NSR0230M2T5G

3.5µH 31.6k CDRH4D22/HP-3R5 VOUT2

22µF AT 1.6A 10V

CURRENT (m A)

DN404 F02

Figure 1. LT3506A Application Circuit Provides Figure 2. Overall Circuit Effi ciency Dual Outputs of 5V at 1.6A and 3.3V at 1.6A (Both Outputs Loaded Identically)