LM2599SX-12/NOPB National Semiconductor, LM2599SX-12/NOPB Datasheet - Page 19

• Manufacturer Part Number: LM2599SX-12/NOPB
• Description: IC REG SW 12V 3A STP DN TO-263-7
• Manufacturer: National Semiconductor
• Series: SIMPLE SWITCHER®r
• Type: Step-Down (Buck)r

Specifications of LM2599SX-12/NOPB

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 12V
• Current - Output: 3A
• Frequency - Switching: 150kHz
• Voltage - Input: 4.5 ~ 40 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: D²Pak, TO-263 (7 leads + tab)
• For Use With: 551011367-021 - BOARD WEBENCH BUILD IT LM2599
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -
• Other names: *LM2599SX-12; *LM2599SX-12/NOPB; LM2599SX-12

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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