551011367-021 National Semiconductor, 551011367-021 Datasheet - Page 19

• Manufacturer Part Number: 551011367-021
• Description: BOARD WEBENCH BUILD IT LM2599
• Manufacturer: National Semiconductor
• Series: WEBENCH® Buildit Boardr

Specifications of 551011367-021

• Main Purpose: DC/DC, Step Down
• Regulator Topology: Buck
• Board Type: Bare (Unpopulated)
• Utilized Ic / Part: LM2599
• Lead Free Status / RoHS Status: Not applicable / Not applicable
• Current - Output: -
• Voltage - Output: -
• Voltage - Input: -
• Power - Output: -
• Frequency - Switching: -
• Outputs And Type: -
• Other names: *551011367-021

Application Information
the narrow pulses and ramp up in a controlled manner. This
is a very useful feature in some switcher topologies that
require large startup currents (such as the inverting configu-
ration) which can load down the input power supply.
Note: The lower curve shown in Figure 13 shows the Soft-start region from
4. Normal operation. Above 2.8V, the circuit operates as a
standard Pulse Width Modulated switching regulator. The
capacitor will continue to charge up until it reaches the
internal clamp voltage of approximately 7V. If this pin is
driven from a voltage source, the current must be limited to
about 1 mA.
If the part is operated with an input voltage at or below the
internal soft-start clamp voltage of approximately 7V, the
voltage on the SD/SS pin tracks the input voltage and can be
disturbed by a step in the voltage. To maintain proper func-
tion under these conditions, it is strongly recommended that
the SD/SS pin be clamped externally between the 3V maxi-
mum soft-start threshold and the 4.5V minimum input volt-
age. Figure 15 is an example of an external 3.7V (approx.)
clamp that prevents a line-step related glitch but does not
interfere with the soft-start behavior of the device.
0% to 100%. This is not the duty cycle percentage, but the output
voltage percentage. Also, the Soft-start voltage range has a negative
temperature coefficient associated with it. See the Soft-start curve in
the electrical characteristics section.
FIGURE 14. Timing Diagram for 5V Output
(Continued)
19
FIGURE 13. Soft-start, Delay, Error, Output
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