DC1021A - Demo Manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1021A
HIGH EFFICIENCY, HIGH POWER BUCK CONVERTER WITH DIFFERENTIAL OUTPUT
SENSING AND TRACKING
LTC3823EUH
DESCRIPTION
Demonstration circuit 1021A is a high efficiency synchronous step-down DC/DC converter with 4.5V to
16V input range. It can provide 2.5V output with 10A
maximum current. The demo board features the
LTC®3823EUH controller. The LTC3823 has a high
accuracy +/-0.67% 0.6V reference voltage and provides many advanced functions including output
tracking, differential output sensing, phase-lock loop
frequency synchronization, programmable current
limit, output over voltage protection and input under
voltage lockout, power good monitor, programmable
soft start, selectable discontinuous operation mode or
forced continuous mode at light load, and adjustable
dead time between the top gate and bottom gate signals to optimize the efficiency.
Design files for this circuit board are available. Call
the LTC factory.
LTC is a registered trademark of Linear Technology Corporation
Table 1. Performance Summary (TA = 25°C)
PARAMETER
CONDITION
VALUE
Input Voltage Range
4.5V to 16V
Output Voltage
VIN = 4.5-16V, IOUT = 0A to 10A,
2.5V ±2%
Maximum load current
VIN = 4.5-16V
10A
Typical Output Ripple
VIN = 12V, IOUT = 10A (20MHz BW)
25mVP–P
Typical Switching Frequency
VIN = 12V, IOUT = 10A
500kHz
OPERATING PRINCIPLES
The LTC3823 uses a constant on-time, valley current
mode control architecture able to deliver very low
duty cycles with fast transient response without requiring a sense resistor. The switching frequency of
the converter can be selected by an external resistor
Ron and is compensated for variations on input supply voltage. An internal phase-lock loop allows the
controller to be synchronized to an external clock.
Figure 3 gives the efficiency curves.
to the external voltage to be tracked. The tracking can
be coincident or ratiometric, as shown in Figure 4.
The LTC3823 has true remote differential output
sensing. When using remote sensing, connect Voutsense+ pin to the positive terminal of the remote output load, and connect Voutsense- pin to the negative
terminal of the remote output load.
The LTC3823 has output voltage up and down tracking capability. Using the track/SS pin, the converter
output can track another supply’s output voltage. To
select tracking function, place JP2 at TRACK, remove
the soft start cap Css and connect a resistor divider
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1021A
HIGH EFFICIENCY, HIGH POWER BUCK CONVERTER WITH DIFFERENTIAL OUTPUT
SENSING AND TRACKING
QUICK START PROCEDURE
Demonstration circuit 1021A is easy to set up to
evaluate the performance of LTC3823. Refer to Figure
1 for proper measurement equipment setup 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. See Figure
2 for proper scope probe technique.
1.
Initial jumper positions:
JP1: DCM (discontinuous mode); JP2: SS (soft start)
2.
With power off, connect the input power supply to
+Vin (4.5V-16V) and GND (input return).
3.
Connect the 2.5V load between Vout and GND. (Initial load: 0 A)
4.
Connect the DVMs to the input and output.
5.
Turn on the input power supply and check for the
proper output voltages. Vout should be 2.5V+/-2%.
6.
Once the proper output voltage is established, adjust the load within the operating range and observe the output voltage regulation, ripple voltage
and other parameters.
Figure 1. Proper Measurement Equipment Setup
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1021A
HIGH EFFICIENCY, HIGH POWER BUCK CONVERTER WITH DIFFERENTIAL OUTPUT
SENSING AND TRACKING
Figure 2. Measuring Input or Output Ripple
12V input to 2.5V output
95
90
efficiency
85
80
FC
75
DCM
70
65
60
0
1
2
3
4
5
6
7
8
9
10
load current (A)
Figure 3. Efficiency vs load current
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1021A
HIGH EFFICIENCY, HIGH POWER BUCK CONVERTER WITH DIFFERENTIAL OUTPUT
SENSING AND TRACKING
(a) Coincident tracking
(b) Ratiometric tracking
Figure 4. (a)(b) Up/down output tracking. Upper waveform: external voltage; lower waveform: output voltage of the converter
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1021A
HIGH EFFICIENCY, HIGH POWER BUCK CONVERTER WITH DIFFERENTIAL OUTPUT
SENSING AND TRACKING
5
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