Datasheet LT3493-3 (Analog Devices) - 8
| Hersteller | Analog Devices |
| Beschreibung | 1.2A, 750kHz Step-Down Switching Regulator in 2mm × 3mm DFN |
| Seiten / Seite | 20 / 8 — APPLICATIO S I FOR ATIO. FB Resistor Network. Input Voltage Range. Figure … |
| Dateiformat / Größe | PDF / 391 Kb |
| Dokumentensprache | Englisch |
APPLICATIO S I FOR ATIO. FB Resistor Network. Input Voltage Range. Figure 1
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LT3493-3
U U W U APPLICATIO S I FOR ATIO FB Resistor Network
The maximum input voltage is determined by the absolute maximum ratings of the V The output voltage is programmed with a resistor divider IN and BOOST pins. For con- stant-frequency operation, the maximum input voltage is between the output and the FB pin. Choose the 1% determined by the minimum duty cycle, DC resistors according to: MIN = 0.10. If the duty cycle requirement is less than DCMIN, the part will V ⎞ enter pulse-skipping mode. The onset of pulse-skipping R = ⎛ R OUT 1 2 – 1 ⎝⎜ occurs at: 0 78V ⎠⎟ . V V R2 should be 20k or less to avoid bias current errors. V OUT D = + V + V IN P ( S) – D SW DC Reference designators refer to the Block Diagram. MIN An optional phase lead capacitor of 22pF between V In pulse-skipping mode, the part skips pulses to control OUT and FB reduces light-load output ripple. the inductor current and regulate the output voltage, possibly producing a spectrum of frequencies below
Input Voltage Range
750kHz. The input voltage range for LT3493-3 applications de- Note that this is a restriction on the operating input voltage pends on the output voltage and on the absolute maximum to remain in constant-frequency operation; the circuit will ratings of the VIN and BOOST pins. tolerate transient inputs up to the absolute maximum ratings of the V The minimum input voltage is determined by either the IN and BOOST pins when the output is in regulation. The input voltage should be limited to V LT3493-3’s minimum operating voltage of 6.8V, or by its IN(PS) during overload conditions (short-circuit or start-up). maximum duty cycle. The duty cycle is the fraction of time that the internal switch is on and is determined by the input and output voltages: VSW V V OUT D 20V/DIV DC = + V – V + V IN SW D IL where VD is the forward voltage drop of the catch diode 0.5A/DIV (~0.4V) and VSW is the voltage drop of the internal switch (~0.4V at maximum load). This leads to a minimum input VOUT 200mV/DIV voltage of: AC COUPLED COUT = 10µF 2µs/DIV 3493-3 F01 V V V OUT D OUT = 3V V = + V + V V IN MIN ( ) – D SW IN = 30V DC ILOAD = 0.75A MAX L = 10µH with DCMAX = 0.91 (0.88 over temperature).
Figure 1
3493-3f 8
U U W U APPLICATIO S I FOR ATIO FB Resistor Network
The maximum input voltage is determined by the absolute maximum ratings of the V The output voltage is programmed with a resistor divider IN and BOOST pins. For con- stant-frequency operation, the maximum input voltage is between the output and the FB pin. Choose the 1% determined by the minimum duty cycle, DC resistors according to: MIN = 0.10. If the duty cycle requirement is less than DCMIN, the part will V ⎞ enter pulse-skipping mode. The onset of pulse-skipping R = ⎛ R OUT 1 2 – 1 ⎝⎜ occurs at: 0 78V ⎠⎟ . V V R2 should be 20k or less to avoid bias current errors. V OUT D = + V + V IN P ( S) – D SW DC Reference designators refer to the Block Diagram. MIN An optional phase lead capacitor of 22pF between V In pulse-skipping mode, the part skips pulses to control OUT and FB reduces light-load output ripple. the inductor current and regulate the output voltage, possibly producing a spectrum of frequencies below
Input Voltage Range
750kHz. The input voltage range for LT3493-3 applications de- Note that this is a restriction on the operating input voltage pends on the output voltage and on the absolute maximum to remain in constant-frequency operation; the circuit will ratings of the VIN and BOOST pins. tolerate transient inputs up to the absolute maximum ratings of the V The minimum input voltage is determined by either the IN and BOOST pins when the output is in regulation. The input voltage should be limited to V LT3493-3’s minimum operating voltage of 6.8V, or by its IN(PS) during overload conditions (short-circuit or start-up). maximum duty cycle. The duty cycle is the fraction of time that the internal switch is on and is determined by the input and output voltages: VSW V V OUT D 20V/DIV DC = + V – V + V IN SW D IL where VD is the forward voltage drop of the catch diode 0.5A/DIV (~0.4V) and VSW is the voltage drop of the internal switch (~0.4V at maximum load). This leads to a minimum input VOUT 200mV/DIV voltage of: AC COUPLED COUT = 10µF 2µs/DIV 3493-3 F01 V V V OUT D OUT = 3V V = + V + V V IN MIN ( ) – D SW IN = 30V DC ILOAD = 0.75A MAX L = 10µH with DCMAX = 0.91 (0.88 over temperature).
Figure 1
3493-3f 8