Linear LTC1704, LTC1704B Quick Start Manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 357

550KHZ SYNCHRONOUS BUCK CONVERTER AND LINEAR REGULATOR

DESCRIPTION

LTC1704/LTC1704B

Demonstration circuit 357 is a dual
power supply with one switcher and
one LDO regulator. It features the
LTC1704 and LTC1704B. The LTC1704
version features burst mode operation
at light load. The B version does not
have burst mode. The input voltage is
5V nominal, the switcher output is
set at 1.8V by a feedback resistor
divider and the LDO output is set at

1.5V by its feedback resistor di­vider. The switcher uses Mosfet R

Table 1. PERFORMANCE SUMMARY

PARAMETER CONDITION VALUE

Minimum Input Voltage 4.75V

Maximum Input Voltage 5.5V

V

V

OUT1

V

V

OUT2

Typical V

Nominal Switching Frequency 550kHz

Output Ripple VIN = 5V, I

OUT1

= 4.75V to 5.5V, I

IN

IN_LDO

DS(ON)

= 1.8V, I

CORE

for current limit. This improves ef­ficiency and eliminates cost and
power loss of discrete sense resis­tors. The LDO can use the switcher
output or an external supply as its
input. The output voltages can be re­programmed within certain limits in
accordance with LTC1704 specifica­tions.

Design files for this circuit board
are available. Call the LTC factory.

= 0A to 15A 1.8V +2%

OUT1

= 0A to 1.5A 1.5V ±2%

OUT2

= 15A 15mV

P–P

QUICK START PROCEDURE

Demonstration circuit 357 is easy to
set up to evaluate the performance of
the LTC1704. Refer to Figure 1 for

1.

Place jumper JP1 in the ON posi­tion.

2.

Place Jumper JP2 in VOUT1 position.

proper measurement equipment setup,

3.

and follow the procedure below:

NOTE:

When measuring the input or out­put voltage ripple, care must be
taken to avoid a long ground lead on
the oscilloscope probe. Measure the
input or output voltage ripple by
touching the probe tip directly
across the Vin or Vout and GND termi­nals.

With power off, connect the input
power supply to Vin and GND, making
sure voltage is not set greater
than 6V.

4.

Turn on the power at the input. Set
Vin=5V

5.

Check for the proper output volt­ages. Vout1 = 1.764V to 1.836V,
Vout2 = 1.470V to 1.530V

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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 357

550KHZ SYNCHRONOUS BUCK CONVERTER AND LINEAR REGULATOR

If there is no output, temporarily
disconnect the load to make sure
that the load is not set too high.

6.

Once the proper output voltages are
established, adjust the loads

within the operating range and ob­serve the output voltage regula­tion, ripple voltage, efficiency,
and other parameters.

Figure 1. DC357 Hookup Diagram

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