Datasheet LT1931, LT1931A (Analog Devices) - 8
| Hersteller | Analog Devices |
| Beschreibung | 1.2MHz/2.2MHz Inverting DC/DC Converters in ThinSOT |
| Seiten / Seite | 12 / 8 — APPLICATIO S I FOR ATIO. DIODE SELECTION. Figure 8. RSS = 15k, CSS = … |
| Dateiformat / Größe | PDF / 459 Kb |
| Dokumentensprache | Englisch |
APPLICATIO S I FOR ATIO. DIODE SELECTION. Figure 8. RSS = 15k, CSS = 33nF; VOUT Reaches – 5V in 1ms;
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LT1931/LT1931A
U U W U APPLICATIO S I FOR ATIO DIODE SELECTION
VOUT 2V/DIV A Schottky diode is recommended for use with the LT1931/ LT1931A. The Motorola MBR0520 is a very good choice. Where the input to output voltage differential exceeds 20V, IIN 0.5A/DIV use the MBR0530 (a 30V diode). These diodes are rated to AC COUPLED 5V handle an average forward current of 0.5 A. In applications VSS 0V where the average forward current of the diode exceeds 200µs/DIV 1931 F08 0.5A, a Microsemi UPS5817 rated at 1A is recommended.
Figure 8. RSS = 15k, CSS = 33nF; VOUT Reaches – 5V in 1ms; Input Current Peaks at 500mA LAYOUT HINTS
The high-speed operation of the LT1931/LT1931A de- VOUT mands careful attention to board layout. You will not get 2V/DIV advertised performance with careless layout. Figure 10 shows the recommended component placement. The IIN 0.5A/DIV ground cut at the cathode of D1 is essential for low noise AC COUPLED operation. 5V VSS 0V 500µs/DIV 1931 F09
Figure 9. RSS = 15k, CSS = 68nF; VOUT Reaches – 5V in 1.6ms; Input Current Peaks at 350mA
L1B L1A C1 –VOUT + increased to 68nF, resulting in a lower peak input current D1 C2 of 350mA with a VOUT ramp time of 1.6ms. CSS or RSS can V + IN C3 be increased further for an even slower ramp, if desired. 1 5 Diode D2 serves to quickly discharge CSS when VSS is 2 driven low to shut down the device. D2 can be omitted, 3 4 SHUTDOWN resulting in a “soft-stop” slow discharge of the output R2 capacitor. R1 GND 1931 F10
Figure 10. Suggested Component Placement. Note Cut in Ground Copper at D1’s Cathode
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U U W U APPLICATIO S I FOR ATIO DIODE SELECTION
VOUT 2V/DIV A Schottky diode is recommended for use with the LT1931/ LT1931A. The Motorola MBR0520 is a very good choice. Where the input to output voltage differential exceeds 20V, IIN 0.5A/DIV use the MBR0530 (a 30V diode). These diodes are rated to AC COUPLED 5V handle an average forward current of 0.5 A. In applications VSS 0V where the average forward current of the diode exceeds 200µs/DIV 1931 F08 0.5A, a Microsemi UPS5817 rated at 1A is recommended.
Figure 8. RSS = 15k, CSS = 33nF; VOUT Reaches – 5V in 1ms; Input Current Peaks at 500mA LAYOUT HINTS
The high-speed operation of the LT1931/LT1931A de- VOUT mands careful attention to board layout. You will not get 2V/DIV advertised performance with careless layout. Figure 10 shows the recommended component placement. The IIN 0.5A/DIV ground cut at the cathode of D1 is essential for low noise AC COUPLED operation. 5V VSS 0V 500µs/DIV 1931 F09
Figure 9. RSS = 15k, CSS = 68nF; VOUT Reaches – 5V in 1.6ms; Input Current Peaks at 350mA
L1B L1A C1 –VOUT + increased to 68nF, resulting in a lower peak input current D1 C2 of 350mA with a VOUT ramp time of 1.6ms. CSS or RSS can V + IN C3 be increased further for an even slower ramp, if desired. 1 5 Diode D2 serves to quickly discharge CSS when VSS is 2 driven low to shut down the device. D2 can be omitted, 3 4 SHUTDOWN resulting in a “soft-stop” slow discharge of the output R2 capacitor. R1 GND 1931 F10
Figure 10. Suggested Component Placement. Note Cut in Ground Copper at D1’s Cathode
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