LM20333EVAL National Semiconductor, LM20333EVAL Datasheet - Page 2

• Manufacturer Part Number: LM20333EVAL
• Description: EVALUATION BOARD FOR THE LM20333
• Manufacturer: National Semiconductor
• Series: PowerWise®r

Specifications of LM20333EVAL

• Main Purpose: DC/DC, Step Down
• Outputs And Type: 1, Non-Isolated
• Voltage - Output: 3.3V
• Current - Output: 3A
• Voltage - Input: 4.5 ~ 25V
• Regulator Topology: Buck
• Board Type: Fully Populated
• Utilized Ic / Part: LM20333
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -
• Frequency - Switching: -

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Powering and Loading
Considerations
Read this entire page prior to attempting to power the evalu-
ation board.
QUICK SETUP PROCEDURE
Step 1: Set the input source current limit to 3A. Turn off the
input source. Connect the positive output of the input source
to J1 and the negative output to J2.
Step 2: Connect the load, with 3A capability, to J3 for the
positive connection and J4 for the negative connection.
Step 3: The ENABLE pin, J5, should be left open for normal
operation.
Step 4: Set the input source voltage to 12V and the load to
0.1A. The load voltage should be in regulation with a nominal
3.3V output.
Step 5: Slowly increase the load while monitoring the load
voltage at J3 and J4. It should remain in regulation with a
nominal 3.3V output as the load is increased up to 3 Amp.
Step 6: Slowly sweep the input source voltage from 4.5V to
25V. The load voltage should remain in regulation with a
nominal 3.3V output. If desired the output of the device can
be disabled by connecting the ENABLE pin (J5) to GND (J8).
TP1 (VOUT)
Silkscreen
Terminal
ENABLE
SS/TRK
PGOOD
VOUT
SYNC
GND
JP1
VIN
SW
This terminal is the input voltage to the device. The evaluation board will operation over the input voltage
range of 4.5V to 25V. This voltage is limited due to the voltage rating of the input capacitors.
These terminals are the ground connections to the device. There are three different GND connections on
the PCB. J2 should be used for the input supply, J4 should be used for the load, and J8 should be used
for low power signal connections such as ENABLE.
This terminal connects to the output voltage of the power supply and should be connected to the load.
This terminal connects to the enable pin of the device. This terminal can be left floating or driven externally.
If driven externally, a voltage typically less than 1.2V will disable the device. The operating voltage for this
pin should not exceed 5.5V. The absolute maximum voltage rating on this pin is 6V.
This terminal provides access to the SS/TRK pin of the device. Connections to this terminal are not needed
for most applications. The feedback pin of the device will track the voltage on the SS/TRK pin if it is driven
with an external voltage source that is below the 0.8V reference. The voltage on this pin should not exceed
5.5V during normal operation. The absolute maximum voltage rating on this pin is 6V.
This terminal connects to the power good output of the device. There is an option to connect this pin to
VOUT or VCC through a 10 kΩ pull-up resistor. The voltage on this pin should not exceed 5.5V during
normal operation and has an absolute maximum voltage rating of 6V.
This terminal block selects the pull-up voltage for the PGOOD pin to be either VCC or VOUT. An external
voltage source for PGOOD may be supplied by connecting to the center terminal. The voltage applied to
PGOOD should not exceed 5.5V during normal operation and has an absolute maximum voltage rating of
6V.
This terminal allows easy probing of the switch node. Do not apply any external voltage source to this pin.
This is a oscilloscope probe connector point used to measure the output ripple and transient response. It
is design to work with most Tektronix oscilloscope probes and is the recommended measurement point for
evaluating AC performance.
This terminal connects to the SYNC pin of the device. If this pin is left open the switching frequency will
default to approximately 200kHz. The voltage on this pin should not exceed 5.5V during normal operation
and has an absolute maximum voltage rating of 6V.
Connection Descriptions
2
Step 7: The pull-up voltage for PGOOD can be selected by
using the JP1 shunt to connect VPULLUP to VOUT or VCC.
Step 8: The frequency of operation can be varied as desired
by connecting a signal
POWERING UP
It is suggested that the load power be kept low during the first
power up. Set the current limit of the input source to provide
about 1.5 times the anticipated wattage of the load. Once the
device is powered up, immediately check for 3.3 volts at the
output.
A quick efficiency check is the best way to confirm that ev-
erything is operating properly. If something is amiss you can
be reasonably sure that it will affect the efficiency adversely.
Few parameters can be incorrect in a switching power supply
without creating losses and potentially damaging heat.
OVER CURRENT PROTECTION
The evaluation board is configured with cycle-by-cycle over-
current protection. This function is completely contained in the
LM20333. The peak current is limited to approximately 5.2A.
Description