LM20333EVAL National Semiconductor, LM20333EVAL Datasheet - Page 6

• 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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For stability purposes the device should be compensated for
the maximum output current expected in the application.
OPTIONAL COMPENSATION CAPACITOR: C7
A second compensation capacitor C7 can be used in some
designs to improve noise immunity for low duty cycle conver-
sions, as well as, provide a high frequency pole, useful for
cancelling a possible zero introduced by the ESR of the output
capacitor. For the LM20333 evaluation board, a 10pF capac-
itor is populated for C7. Higher value capacitors can be used
to improve low duty cycle performance at the expense of
phase margin.
FEEDBACK RESISTORS: R4, R5, and R6
The resistors labeled R5 and R6 create a voltage divider from
V
voltage regulator. Nominally, the output of the LM20333 eval-
uation board is set to 3.3V, giving resistor values of R5 = 30.9
kΩ and R6 = 10 kΩ. If a different output voltage is required,
the value of R5 can be adjusted according to the equation:
OUT
to the feedback pin that is used to set the output of the
6
R6 does not need to be changed from its value of 10 kΩ. Re-
sistor R4 has a value of 348Ω and is provided as an injection
point for loop stability measurements, as well as, a way to
further tweak the output voltage accuracy to account for re-
sistor tolerance values differing from ideal calculated values.
PROGRAMMABLE UVLO: R2 and R3
The resistors labeled R2 and R3 create a voltage divider from
V
threshold or UVLO of the voltage regulator. To allow evalua-
tion of the device down to 4.5V these components are not
installed. To change the turn-on threshold of the device a 10
kΩ resistor is recommended for R3 and the value of R2 can
be calculated using the equation:
IN
to the enable pin that can be used to set the turn-on