DC836A - Demo Manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 836
NO RSENSE CONSTANT FREQUENCY STEP-DOWN DC/DC CONTROLLER IN 3X2 DFN
LTC3772
DESCRIPTION
Demonstration circuit 836 is a No RSENSE™ constant
frequency step-down DC/DC converter featuring the
LTC3772 Controller in a 3mm×2mm DFN package.
The demo board generates 2A output current at one
of the three output voltages: 1.8V, 2.5V or 3.3V. The
output voltage is selectable by JP1. Higher output
current is made possible using optional components.
The exclusive use of surface mount components results in a highly efficient application in a very small
board space. The demo board highlights the capabilities of the LTC3772, which uses current mode architecture to drive an external P-channel power
MOSFET. This results in fast loop dynamics and transient response. The ON resistance of the MOSFET is
used to sense the switch current. No additional
sense resistor is needed. The LTC3772’s internal
soft-start reduces the maximum input current during
start up. To maximize the runtime from a battery
source, the MOSFET is turned on continuously in
dropout (100% duty cycle). The peak current sense
voltage can be configured into three different voltage
thresholds for different loads. The LTC3772 enters
Burst Mode™ at light loads, enhancing the efficiency
in this mode. If the output is shorted to ground, the
frequency is folded back to prevent current runaway.
High efficiency over wide load conditions and compact size make the LTC3772 ideal for portable applications.
The LTC3772 datasheet gives a complete description
of the part, operation and application information.
The datasheet must be read in conjunction with this
quick start guide for demo circuit 836.
Design files for this circuit board are available.
Call the LTC factory.
, LTC and LT are registered trademarks of Linear Technology Corporation.
PERFORMANCE SUMMARY
Specifications are at TA = 25°C
SYMBOL
IQ
VIN
PARAMETER
Input DC Current in Shutdown Mode
Input Voltage
CONDITIONS
VITH/RUN = 0V, VIN = 4.2V
VOUT = 1.8V
VOUT = 2.5V
VOUT = 3.3V
VOUT
Output Voltage
IOUT
EFF
Output Current
Efficiency
VPP
OUTPUT VOLTAGE RIPPLE
ILOAD = 2A, JP1 on 1.8V position
ILOAD = 2A, JP1 on 2.5V position
ILOAD = 2A, JP1 on 3.3V position
VIN = 3V, VOUT = 1.8V, IOUT = 2A
VIN = 3V, VOUT = 2.5V, IOUT = 2A
VIN = 4V, VOUT = 3.3V, IOUT = 2A
VIN = 8V, VOUT = 3.3V, IOUT = 2A
MIN
2.75
3
3.5
1.728
2.4
3.168
TYP
8
MAX
20
8*
8*
UNITS
uA
V
8*
1.8
2.5
3.3
1.872
2.6
3.432
2
86%
92%
94%
22
V
A
mV
*: The maximum VIN is limited by the MOSFET gate voltage. The maximum VIN of LTC3772 is rated at 9.8V.
1
LTC3772
QUICK START PROCEDURE
Demonstration circuit 836 is easy to set up to evaluate the performance of the LTC3772. 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.
NOTE: Make
ceed 8V.
4.
2.
With power off, connect the input power supply to
VIN and GND and the load to VOUT and GND.
3.
Turn on the power at the input.
Check for the proper output voltages per the JP1
setup.
NOTE: If
there is no output, temporarily disconnect
the load to make sure that the load is not set too
high.
5.
Once the proper output voltages are established,
adjust the loads within the operating range and observe the output voltage regulation, ripple voltage,
efficiency and other parameters.
6.
To evaluate output current higher than 2A, the
footprints on the bottom side of the board can be
used. Refer to the datasheet for more application
examples.
Place jumpers in the following positions:
One of three positions (1.8V, 2.5V or
JP1
3.3V)
sure that the input voltage does not ex-
Figure 1. Proper Measurement Equipment Setup
GND
VIN
Figure 2. Measuring Input or Output Ripple
2
LTC3772
3
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