Datasheet LTC3617 (Analog Devices) - 10
| Fabricante | Analog Devices |
| Descripción | ±6A Monolithic Synchronous Step-Down Regulator for DDR Termination |
| Páginas / Página | 20 / 10 — applications inForMation. Operating Frequency. Frequency Synchronization. … |
| Formato / tamaño de archivo | PDF / 487 Kb |
| Idioma del documento | Inglés |
applications inForMation. Operating Frequency. Frequency Synchronization. Figure 2. Setting Switching Frequency
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LTC3617
applications inForMation
The basic LTC3617 application circuit is shown in Figure 1. Tying the RT pin to SVIN sets the default internal operating frequency to 2.25MHz ±20%.
Operating Frequency
Selection of the operating frequency is a trade-off between
Frequency Synchronization
efficiency and component size. High frequency operation The LTC3617’s internal oscillator can be synchronized to allows the use of smaller inductor and capacitor values. an external frequency by applying a square wave clock Operation at lower frequencies improves efficiency by signal to the SYNC pin. During synchronization, the top reducing internal gate charge losses but requires larger switch turn-on is locked to the falling edge of the external inductance values and/or capacitance to maintain low frequency source. The synchronization frequency range output voltage ripple. is 300kHz to 4MHz. The operating frequency of the LTC3617 is determined The frequency set by the resistor on the RT pin should be by an external resistor that is connected between the RT the same as the external clock frequency to ensure the pin and ground. The value of the resistor sets the ramp internal oscillator properly adjusts when the clock signal current that is used to charge and discharge an internal is applied or removed. timing capacitor within the oscillator and can be calculated VIN by using the following equation: LTC3617 SVIN f RT OSC 3.82 • 1011Hz 2.25MHz R SYNC T = SGND fOSC H ( z) Ω–16kΩ Although frequencies as high as 4MHz are possible, the minimum on-time of the LTC3617 imposes a minimum VIN LTC3617 limit on the operating duty cycle. The minimum on-time SVIN 0.4V is typically 80ns; therefore, the minimum duty cycle is RT fOSC ∝1/RT equal to 80ns • f SYNC OSC(Hz)•100%. RT SGND VIN 2.5V CIN VIN 22µF LTC3617 SVIN PVIN ×4 R SV T IN RUN VTTR f RT OSC RPG VDDQIN VTTR 1.25V 1/TP 100k RT 0.1µF ±10mA SYNC RT SGND 365k LTC3617 L1 0.33µH VOUT SW 1.25V 1.2V 0.3V PGOOD PGOOD SGND COUT ±6A 100µF T R P C 3617 F02 10k ITH PGND C C C1 C 10pF SYNC VFB 680pF
Figure 2. Setting Switching Frequency
(OPT) 3617 F01
Figure 1. 1.25V, ±6A at 1MHz from 2.5V
3617fa 10 Document Outline Features Applications Description Typical Application Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Pin Functions Functional Block Diagram Operation Applications Information Typical Applications Package Description Revision History Typical Application Related Parts
applications inForMation
The basic LTC3617 application circuit is shown in Figure 1. Tying the RT pin to SVIN sets the default internal operating frequency to 2.25MHz ±20%.
Operating Frequency
Selection of the operating frequency is a trade-off between
Frequency Synchronization
efficiency and component size. High frequency operation The LTC3617’s internal oscillator can be synchronized to allows the use of smaller inductor and capacitor values. an external frequency by applying a square wave clock Operation at lower frequencies improves efficiency by signal to the SYNC pin. During synchronization, the top reducing internal gate charge losses but requires larger switch turn-on is locked to the falling edge of the external inductance values and/or capacitance to maintain low frequency source. The synchronization frequency range output voltage ripple. is 300kHz to 4MHz. The operating frequency of the LTC3617 is determined The frequency set by the resistor on the RT pin should be by an external resistor that is connected between the RT the same as the external clock frequency to ensure the pin and ground. The value of the resistor sets the ramp internal oscillator properly adjusts when the clock signal current that is used to charge and discharge an internal is applied or removed. timing capacitor within the oscillator and can be calculated VIN by using the following equation: LTC3617 SVIN f RT OSC 3.82 • 1011Hz 2.25MHz R SYNC T = SGND fOSC H ( z) Ω–16kΩ Although frequencies as high as 4MHz are possible, the minimum on-time of the LTC3617 imposes a minimum VIN LTC3617 limit on the operating duty cycle. The minimum on-time SVIN 0.4V is typically 80ns; therefore, the minimum duty cycle is RT fOSC ∝1/RT equal to 80ns • f SYNC OSC(Hz)•100%. RT SGND VIN 2.5V CIN VIN 22µF LTC3617 SVIN PVIN ×4 R SV T IN RUN VTTR f RT OSC RPG VDDQIN VTTR 1.25V 1/TP 100k RT 0.1µF ±10mA SYNC RT SGND 365k LTC3617 L1 0.33µH VOUT SW 1.25V 1.2V 0.3V PGOOD PGOOD SGND COUT ±6A 100µF T R P C 3617 F02 10k ITH PGND C C C1 C 10pF SYNC VFB 680pF
Figure 2. Setting Switching Frequency
(OPT) 3617 F01
Figure 1. 1.25V, ±6A at 1MHz from 2.5V
3617fa 10 Document Outline Features Applications Description Typical Application Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Pin Functions Functional Block Diagram Operation Applications Information Typical Applications Package Description Revision History Typical Application Related Parts