DC922A - Demo Manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 922
2-PHASE DUAL SYNCHRONOUS STEP-DOWN CONVERTER WITH OUTPUT TRACKING
LTC3736EUF-2
DESCRIPTION
Demonstration circuit 922A is a 2-phase dual synchronous high efficiency step-down DC/DC converter
with 2.75V to 8V input range. It has two outputs: 2.5V
(6A MAX) and 1.8V (6A MAX). The demo circuit features the LTC®3736EUF-2 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.
frequency can also be selected with the PLLLPF pin.
Tying the PLLLPF pin to GND selects 300KHz operation; tying the PLLLPF pin to VIN selects 750KHz operation.
The demo circuit has a tracking function, allowing
VOUT2 to track VOUT1 during start-up.
Design files for this circuit board are available. Call
the LTC factory.
Switching frequency is internally set at 550KHz. For
noise sensitive applications, the converter can be externally synchronized from 250KHz to 850KHz. The
, LTC and LT are registered trademarks of Linear Technology Corporation.
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 6A,
2.5V ±2.5%
IOUT2 = 0A to 6A
VOUT2
VIN = 2.75-8V, IOUT1 = 0A to 6A,
1.8V ±2.5%
IOUT2 = 0A to 6A
Typical Output Ripple VOUT1
VIN = 3.3V, IOUT1 = 3A (20MHz BW)
22mVP–P
Typical Output Ripple VOUT2
VIN = 3.3V, IOUT2 = 3A (20MHz BW)
12mVP–P
Typical Switching Frequency
PLLLPF Pin Floating
550kHz
QUICK START PROCEDURE
Demonstration circuit 922A is easy to set up to evaluate the performance of the LTC3736EUF-2. Refer to
Figure 1 for proper measurement equipment setup
and follow the procedure below:
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.
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
Figure 1) between Vout2 and GND. (Initial loads:
no load.)
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+/2.5%. Vout2 should be 1.8V+/-2.5%.
NOTE: When
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 922
2-PHASE DUAL SYNCHRONOUS STEP-DOWN CONVERTER WITH OUTPUT TRACKING
5.
Once the proper output voltages are established,
adjust the loads within the operating range and ob-
serve the output voltage regulation, ripple voltage
and other parameters.
Figure 1. Proper Measurement Equipment Setup
Figure 2. Measuring Input or Output Ripple
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 922
2-PHASE DUAL SYNCHRONOUS STEP-DOWN CONVERTER WITH OUTPUT TRACKING
2.5Vout Efficiency
3.3Vin,
Cont
95.0%
90.0%
5Vin, Cont
Efficiency (%)
85.0%
80.0%
75.0%
3.3Vin,
Pulse Skip
70.0%
65.0%
5Vin,
Pulse Skip
60.0%
55.0%
50.0%
0
2
4
6
8
10
Load Current (A)
Efficiency (%)
1.8Vout Efficiency
3.3Vin,
Cont
95.0%
90.0%
85.0%
80.0%
75.0%
70.0%
65.0%
60.0%
55.0%
50.0%
5Vin, Cont
3.3Vin,
Pulse Skip
5Vin, Pulse
Skip
0
2
4
6
8
10
Load Current (A)
Figure 3. Efficiency vs load current (550KHz)
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 922
2-PHASE DUAL SYNCHRONOUS STEP-DOWN CONVERTER WITH OUTPUT TRACKING
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