LM20145EVAL National Semiconductor, LM20145EVAL Datasheet - Page 11

• Manufacturer Part Number: LM20145EVAL
• Description: BOARD EVAL 5A POWERWISE LM20145
• Manufacturer: National Semiconductor
• Series: PowerWise®r

Specifications of LM20145EVAL

• Main Purpose: DC/DC, Step Down
• Outputs And Type: 1, Non-Isolated
• Voltage - Output: 1.2V
• Current - Output: 5A
• Voltage - Input: 2.95 ~ 5.5V
• Regulator Topology: Buck
• Frequency - Switching: 500kHz
• Board Type: Fully Populated
• Utilized Ic / Part: LM20145
• Lead Free Status / RoHS Status: Not applicable / Not applicable
• Power - Output: -

perature is exceeded. When activated, typically at 160°C, the
LM20145 tri-states the power FETs and resets soft start. After
the junction cools to approximately 150°C, the part starts up
using the normal start up routine. This feature is provided to
prevent catastrophic failures from accidental device over-
heating.
LIGHT LOAD OPERATION
The LM20145 offers increased efficiency when operating at
light loads. Whenever the load current is reduced to a point
where the peak to peak inductor ripple current is greater than
two times the load current, the part will enter the diode emu-
lation mode preventing significant negative inductor current.
The point at which this occurs is the critical conduction bound-
ary and can be calculated by the following equation:
FIGURE 1. Modes of Operation for LM20145
11
Several diagrams are shown in Figure 1 illustrating continu-
ous conduction mode (CCM), discontinuous conduction
mode, and the boundary condition.
It can be seen that in diode emulation mode, whenever the
inductor current reaches zero the SW node will become high
impedance. Ringing will occur on this pin as a result of the LC
tank circuit formed by the inductor and the parasitic capaci-
tance at the node. If this ringing is of concern an additional
RC snubber circuit can be added from the switch node to
ground.
At very light loads, usually below 100 mA, several pulses may
be skipped in between switching cycles, effectively reducing
the switching frequency and further improving light-load effi-
ciency.
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