Performance Summary; Quick Start Procedure - Analog Devices DC2779A Demo Manual

DEMO MANUAL DC2779A

PERFORMANCE SUMMARY

SYMBOL PARAMETER
V Input Supply Range
IN
V Output Voltage
OUT
I Maximum Continuous Output Current
OUT
f Switching Frequency
SW
EFF Efficiency

QUICK START PROCEDURE

Demonstration circuit 2779A is easy to set up to evalu-
ate the performance of the LT8644S. 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 output voltage ripple by
touching the probe tip directly across the output capacitor.
See Figure 2 for the proper scope technique.
1. Make sure the Jump JP1 is on the BURST position.
Refer to the schematic.
2. With power off, connect the input power supply to VIN
and GND. If the input EMI filter is desired, connect the
input power supply to VEMI and GND.
3. With power off, connect the load from VOUT+ to VOUT–.
4. Connect the voltage meter across the VIN_SENSE and
measurement, and VOUT+ SENSE and
GND for V
IN
VOUT– SENSE for V
5. Turn on the power at the input.
NOTE: Make sure that the input voltage does not exceed 8V.
6. Check for the proper output voltage (V
NOTE: If there is no output, temporarily disconnect the
load to make sure that the load is not set too high or is
shorted.
2
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Specifications are at T
CONDITIONS
V
IN
V
IN
measurement.
OUT
= 1.2V).
OUT
= 25°C
A
= 5V
= 5V, V = 1.2V, I = 8A
OUT OUT
7. Once the proper output voltage is established, adjust
the load within the operating ranges and observe the
output voltage regulation, ripple voltage, efficiency, and
other parameters.
8. An external clock can be added to the SYNC terminal
when SYNC function is used (JP1 on the FCM/SYNC
position). Please make sure that R2 should be chose
to set the LT8644S switching frequency equal to or
below the lowest SYNC frequency. When JP1 is in FCM/
SYNC position and no external clock is connected to
the SYNC terminal of the board, the SYNC/MODE pin
is floating and the LT8644S runs in forced continuous
mode. JP1 can also set LT8644S in spread spectrum
mode (JP1 on the SPREAD-SPECTRUM position).
9. To test the transient response, connect a signal
generator to PULSE GEN terminal, and add a desired
base load between VOUT+ and VOUT– (LOAD shown
on Figure 1). Adjust the signal generator with a 2ms
period, 5% duty cycle and an amplitude from 1V to 2V
to start. Measure the LOAD STEP voltage to observe
the current (I
LOADSTEP
amplitude of the pulse to provide the desired transient.
Adjust the rising and falling edge of the pulse to provide
the desired ramp rate. Figure 3 shows a load step from
4A to 12A. The 4A base load is added between VOUT+
and VOUT–, while the 8A step load is controlled by
the signal generator at PULSE_GEN and measured at
LOAD_STEP with 0.01V/A ratio.
MIN TYP MAX
2.7 8
1.18 1.2 1.22
16
1.95 2 2.05
90.2
= V /10mΩ). Adjust the
LOAD_STEP
UNITS
V
V
A
MHz
%
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