Linear LTC1704 User manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 357
550KHZ SYNCHRONOUS BUCK CONVERTER AND LINEAR REGULATOR
LTC1704/LTC1704B
DESCRIPTION
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 di-
vider. The switcher uses Mosfet R
DS(ON)
for current limit. This improves ef-
ficiency and eliminates cost and
power loss of discrete sense resis-
tors. The LDO can use the switcher
output or an external supply as its
input. The output voltages can be re-
programmed within certain limits in
accordance with LTC1704 specifica-
tions.
Design files for this circuit board
are available. Call the LTC factory.
Table 1. PERFORMANCE SUMMARY
PARAMETER CONDITION VALUE
Minimum Input Voltage 4.75V
Maximum Input Voltage 5.5V
V
OUT1
V
IN
= 4.75V to 5.5V, I
OUT1
= 0A to 15A 1.8V +2%
V
OUT2
V
IN_LDO
= 1.8V, I
OUT2
= 0A to 1.5A 1.5V ±2%
Typical V
OUT1
Output Ripple V
IN
= 5V, I
CORE
= 15A 15mV
P–P
Nominal Switching Frequency 550kHz
QUICK START PROCEDURE
Demonstration circuit 357 is easy to
set up to evaluate the performance of
the LTC1704. Refer to Figure 1 for
proper measurement equipment setup,
and follow the procedure below:
NOTE:
When measuring the input or out-
put 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 termi-
nals.
1.
Place jumper JP1 in the ON posi-
tion.
2.
Place Jumper JP2 in VOUT1 position.
3.
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 volt-
ages. 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 ob-
serve the output voltage regula-
tion, ripple voltage, efficiency,
and other parameters.
Figure 1. DC357 Hookup Diagram
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 357
550KHZ SYNCHRONOUS BUCK CONVERTER AND LINEAR REGULATOR
Figure 2. Vout1 ripple at 1.8V, 2A (–A version with Burst Mode.)
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 357
550KHZ SYNCHRONOUS BUCK CONVERTER AND LINEAR REGULATOR
20mV/Di
v
Figure 3. Vout1 ripple at 1.8V 15A
Figure 4. Load transient response of Vout1 @ 0-10A (–A version with Burst
Mode)
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 357
550KHZ SYNCHRONOUS BUCK CONVERTER AND LINEAR REGULATOR
Figure 5. Load transient response of Vout1 @ 5-15A (-A with Burst Mode)
VOUT1(1.8V) Efficiency
0
10
20
30
40
50
60
70
80
90
100
0.00 5.00 10.00 15.00
Output Current (Amps)
% Efficiency
Vin=5V
Figure 6. Vout1 Efficiency (-A with Burst Mode)
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 357
550KHZ SYNCHRONOUS BUCK CONVERTER AND LINEAR REGULATOR
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