LM5001ISOEVAL National Semiconductor, LM5001ISOEVAL Datasheet - Page 12

• Manufacturer Part Number: LM5001ISOEVAL
• Description: BOARD EVALUATION LM5001ISO
• Manufacturer: National Semiconductor

Specifications of LM5001ISOEVAL

• Main Purpose: DC/DC, Step Down
• Outputs And Type: 1, Isolated
• Voltage - Output: 5V
• Current - Output: 1A
• Voltage - Input: 16 ~ 42V
• Regulator Topology: Flyback
• Frequency - Switching: 250kHz
• Board Type: Fully Populated
• Utilized Ic / Part: LM5001
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -

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Remote configuration of the controller’s operational modes
can be accomplished with open drain device(s) connected to
the EN pin as shown in Figure 4. A MOSFET or an NPN tran-
sistor connected to the EN pin can force the regulator into the
SOFTSTART
Soft-start (SS) can be implemented with an external capacitor
connected to COMP through a diode as shown in Figure 5.
The COMP discharge MOSFET conducts during Shutdown
and Standby modes to keep the COMP voltage below the
PWM offset (1.3V), which inhibits PWM pulses. The error am-
plifier will attempt to raise the COMP voltage after the EN pin
exceeds the 1.26V standby threshold. Because the error am-
plifier output can only sink current, the internal COMP pull-up
FIGURE 4. Remote Standby and Disable Control
FIGURE 3. Basic EN (UVLO) Configuration
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low power ‘off’ state. Adding a PN diode in the drain (or col-
lector) provides the offset to achieve the standby state. The
advantage of standby is that the VCC LDO is not disabled and
external circuitry powered by VCC remains functional.
resistor (~5 kΩ) will supply the charging current to the SS ca-
pacitor. The SS capacitor will cause the COMP voltage to
gradually increase, until the output voltage achieves regula-
tion and FB assumes control of the COMP and the PWM duty
cycle. The SS capacitor continues charging through a large
resistance, R
the normal error amplifier function. During shutdown, the VCC
diode discharges the SS capacitor.
SS
, preventing the SS circuit from interfering with
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