DC1519A - LINEAR TECHNOLOGY

LT3695

DESCRIPTION

Demonstration circuit 1519A is a monolithic step-dow n

DC/DC sw itching regulator featuring LT

3695EM SE. The

demo board is designed for 5V output from a 6.9V to

36V input w ith transient up to 60V. The w ide input range

of the LT3695 allow s a variety of input sources. The typi-

cal sources are automotive batteries, w all adaptors and

industrial supplies. The sw itching frequency can be pro-

grammed either via oscillator resistor or external clock.

The modes of operation (Burst M ode or synchronization)

are jumper selectable. The Burst M ode operation in-

creases the efficiency at light loads.

The LT3695 tolerates adjacent pin shorts or an open pin

w ithout raising the output voltage above its programmed

value. The current mode control scheme creates fast

transient response and good loop stability. The gate drive

of the internal sw itch is boosted to a voltage that is

higher than the Vin to ensure saturation of the sw itch.

The LT3695’s integrated boost diode reduces the parts

count. The R UN/SS pin can be used to set the part in

micropow er shutdow n mode, reducing the supply cur-

rent to less than 1uA. The RUN/SS pin can also be used

to program soft start. In this mode, the RUN/SS pin is

driven through an external RC filter to create a voltage

ramp on this pin. The soft start function reduces the in-

put current surge during start-up.

The LT3695EM SE datasheet gives a complete description

of the part, operation and application information. The

datasheet must be read in conjunction w ith this quick

start guide for demo circuit 1519A.

Design files for this circuit board are available. Call

the LTC factory.

LTM, LTC, LT and µM odule are registered trademarks of Linear Technology Corporation.

All other trademarks are the property of their respective ow ners.

Perform ance Sum m ary for Step-dow n Sw itching Regulator ( TA = 25oC )

PARAM ETER FOR BU CK REGULATOR CONDITION VALUE

M inimum Input Voltage 6.9V

M aximum Input Voltage 36V

Output Voltage V

OUT

+/- 5%

M aximum Output Current 1A

Typical Sw itching Frequency 800kHz

Q U ICK STA RT PROCEDU RE

Demonstration circuit 1519A is easy to set up to evaluate

the performance of the LT3695EM SE. Refer to



Figure 1

for proper measurement equipment setup and follow the

procedure below :

NOTE.

W hen measuring the input or output voltage ripple, care must be

taken to avoid a long ground lead on the oscilloscope probe. M easure the

input or output voltage ripple by touching the probe tip directly across the

Vin or Vout and GND terminals. See



Figure 2 for proper scope probe

technique.

Place JP1 on the ON position.

W ith pow er off, connect the input pow er supply to

Vin and GN D.

Turn on the pow er at the input.

Check for the proper output voltage.

NOTE.

If there is no output, temporarily disconnect the load to make

sure that the load is not set too high.

Once the proper output voltage is established, adjust

the load w ithin the operating range and observe the

DEMO

C IR C U IT

15 19

Q U IC K S TAR T G U IDE

L T 3 6 9 5 EMS E

1A µ P o w e r S te p -d o w n sw itc h in g R e g u

la to r