DC803A - Demo Manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 803
2-PHASE DUAL SYNCHRONOUS STEP-DOWN CONVERTER WITH SPREAD SPECTRUM
AND OUTPUT TRACKING
LTC3736EUF-1
DESCRIPTION
Demonstration circuit 803 is a high efficiency 2-phase
dual synchronous step-down DC/DC converter with
2.75V to 8V input range. It has two outputs: 2.5V (5A
maximum at 5V input) and 1.8V (5A maximum at 5V
input). The demo circuit features the LTC®3736EUF-1
controller. The constant frequency current mode architecture with MOSFET VDS sensing eliminates the
need for sense resistors and improves efficiency. Out
of phase operation significantly reduces input ripple
current as well as the input capacitor size.
to GND selects 300kHz operation; tying FREQ pin to
VIN selects 750kHz operation.
The demo board can be selected to operate in spread
spectrum mode (JP1: Enable) with significantly reduced peak switching noise. The board has tracking
function too, allowing VOUT2 to track VOUT1 during startup.
Switching frequency is internally set at 550kHz. The
frequency can also be adjusted using FREQ pin (with
spread spectrum operation disabled). Tying FREQ pin
LTC is a trademark of Linear Technology Corporation
Design files for this circuit board are available. Call
the LTC factory.
Table 1. Performance Summary (TA = 25°C)
PARAMETER
CONDITION
VALUE
Input Voltage Range
VOUT1
2.75V to 8V
VIN = 2.75-8V, IOUT1 = 0A to 5A,
2.5V ±3%
IOUT2 = 0A to 5A
VOUT2
VIN = 2.75-8V, IOUT1 = 0A to 5A,
1.8V ±3%
IOUT2 = 0A to 5A
Typical Output Ripple VOUT1
VIN = 3.3V, IOUT1 = 3A (20MHz BW)
20mVP–P
Typical Output Ripple VOUT2
VIN = 3.3V, IOUT2 = 3A (20MHz BW)
14mVP–P
Typical Switching Frequency
FREQ Pin Floating; Spread Spectrum: Disable
550kHz
Typical Spread Spectrum Frequency Range
Spread Spectrum: Enable
450kHz- 580kHz
QUICK START PROCEDURE
Demonstration circuit 803 is easy to set up to evaluate the performance of LTC3736-1. 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. (it’s recommended to
measure the output ripple directly at the main output
capacitor).
1.
With power off, connect the input power supply to
+Vin (2.75V-8V) and GND (input return).
2.
Connect the 2.5V load (Load 1 in Figure 1) between
Vout1 and GND; connect the 1.8V load (Load 2 in
1
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 803
2-PHASE DUAL SYNCHRONOUS STEP-DOWN CONVERTER WITH SPREAD SPECTRUM
AND OUTPUT TRACKING
Figure 1) between Vout2 and GND. (Initial loads:
0A)
3.
Connect the DVMs to the input and outputs.
4.
Turn on the input power supply and check for the
proper output voltages. Vout1 should be 2.5V+/3%. Vout2 should be 1.8V+/-3%.
5.
Once the proper output voltages are established,
adjust the loads within the operating range and observe the output voltage regulation, ripple voltage
and other parameters.
Figure 1. Proper Measurement Equipment Setup
2
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 803
2-PHASE DUAL SYNCHRONOUS STEP-DOWN CONVERTER WITH SPREAD SPECTRUM
AND OUTPUT TRACKING
100
V o=2.5V
EFFICIENCY (%)
90
V o=1.8V
80
70
60
50
V in=3.3V
40
1
10
100
1k
10k
LO A D C U R R E N T (mA )
Figure 2. Efficiency vs load current (550kHz)
3
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 803
2-PHASE DUAL SYNCHRONOUS STEP-DOWN CONVERTER WITH SPREAD SPECTRUM
AND OUTPUT TRACKING
4
Similar pages