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dc2373af

DEMO MANUAL DC2373A

Description

LT8641

65V, 3.5A Micropower Synchronous

Step-Down Silent Switcher

Demonstration circuit 2373A is a 65V, 3.5A micropower

synchronous step-down Silent Switcher® with spread

spectrum frequency modulation featuring the LT®8641.

The demo board is designed for 5V output from a 5.5V to

65V input. The wide input range allows a variety of input

sources, such as automotive batteries and industrial sup-

plies. The LT8641 is a compact, ultralow emission, high

efficiency, high speed synchronous monolithic step-down

switchingregulatorthatconsumesonly 2.5μAofquiescent

current when output is regulated at 5V. Top and bottom

power switches, compensation components and other

necessary circuits are inside of the LT8641 to minimize

external components and simplify design.

The SYNC pin on the demo board is grounded by default

for low ripple burst mode operation. Move JP1 to PULSE

SKIPPING position can change the operation mode to

pulse-skipping operation. Once JP1 is on SPREAD SPEC-

TRUM position, VCC is applied to the SYNC pin for low

EMI spread spectrum operation. To synchronous to an

external clock, move JP1 to SYNC and apply the external

clock to the SYNC turret. Figure 1 shows the efficiency of

the circuit at 12V and 24V input in Burst Mode® operation

(input from VIN turret pin). Figure 2 shows the LT8641

L

, LT, LTC, LTM, Linear Technology, Silent Switcher, Burst Mode and the Linear logo are

registered trademarks of Linear Technology Corporation. All other trademarks are the property

of their respective owners.

performance summary

temperature rising on DC2373A demo board under differ-

ent load conditions. The rated maximum load current is

3.5A, while derating is necessary for certain input voltage

and thermal conditions.

The demo board has an EMI filter installed. Under burst

and spread spectrum operation, the EMI performances of

the board (with EMI filter) are shown in Figure 3 and 4. The

red lines in Figure 3 and 4 are CISPR25 Class5 peak limit.

To achieve EMI/EMC performance as shown in Figure 3

and 4, the input EMI filter is required and the input voltage

should be applied at VEMI turret pin.

This board is suitable for a wide range of automotive,

telecom, industrial, and other applications.

The LT8641 data sheet gives a complete description of

the part, operation and application information. The data

sheet must be read in conjunction with this demo manual

for DC2373A.

Design files for this circuit board are available at

http://www.linear.com/demo/DC2373A

Specifications are at TA = 25°C

SYMBOL

PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

VIN

Input Voltage Range

5.5

65

V

VOUT

Output Voltage

4.8

5

5.2

V

IOUT

Maximum Output Current

Derating Is Necessary for Certain VIN and

Thermal Conditions

3.5

A

fSW

Switching Frequency

1.85

2

2.15

MHz

EFF

Efficiency

VIN = 12V, IOUT = 1A

94

%