The switching frequency of the TPS2584x-Q1 can be programmed by the resistor R_T from the RT/SYNC pin and GND pin. Use Equation 3 to determine the RT resistance for a given switching frequency.

Equation 3.

Figure 10-6 RT Set Resistor vs Switching Frequency

Table 10-1 lists typical RT resistors values.

TPS2584x-Q1 switching action can be synchronized to an external clock from 300 kHz to 2.3 MHz. The RT/SYNC pin can be used to synchronize the internal oscillator to an external clock. The internal oscillator can be synchronized by AC coupling a positive edge into the RT/SYNC pin. The AC coupled peak-to-peak voltage at the RT/SYNC pin must exceed the SYNC amplitude threshold of 3.5 V (typical) to trip the internal synchronization pulse detector, and the minimum SYNC clock ON and OFF time must be longer than 100 ns (typical). When using a low impedance signal source, the frequency setting resistor, R_T, is connected in parallel with an AC coupling capacitor, C_COUP, to a termination resistor, R_TERM (for example: 50 Ω). The two resistors in series provide the default frequency setting resistance when the signal source is turned off. A 10-pF ceramic capacitor can be used for C_COUP. Figure 10-7 show the device synchronized to an external clock.

Figure 10-7 Synchronize to External Clock

To avoid AM radio frequency brand and maintain proper regulation when minimum ON-time or minimum OFF-time is reached, the TPS2584x-Q1 implement frequency foldback scheme depends on VIN voltage. Refer to Figure 8-10.

• When 8 V < VIN ≤ 19 V, the switching frequency of TPS2584x-Q1 is determined by R_T resistor or external sync clock.
• When VIN ≤ 8 V, the switching frequency of TPS2584x-Q1 is set to default 420 kHz, regardless of R_T resistor setting or external sync clock.
• When VIN > 19 V, the switching frequency of TPS2584x-Q1 is set to default 420 kHz, regardless of R_T resistor setting or external sync clock.

figure 10-8, figure 10-9 and Figure 10-10 show the device switching frequency and behavior under different VIN voltage and R_T = 8.87 kΩ.

Figure 10-11, Figure 10-12 and Figure 10-13 show the device switching frequency and behavior under different VIN voltage and synchronized to an external 2.1-M system clock.

VIN = 7.5 V

L = 2.2 uH

ILOAD = 3 A

Figure 10-8 Switching Frequency When R_T = 8.87 kΩ

VIN = 20 V

L = 2.2 uH

ILOAD = 3 A

Figure 10-10 Switching Frequency When R_T = 8.87 kΩ

VIN = 13.5 V

L = 2.2 uH

ILOAD = 3 A

Figure 10-12 Synchronizing to External 2.1-MHz Clock

VIN = 13.5 V

L = 2.2 uH

ILOAD = 3 A

Figure 10-9 Switching Frequency When R_T = 8.87 kΩ

VIN = 7.5 V

L = 2.2 uH

ILOAD = 3 A

Figure 10-11 Synchronizing to External 2.1-MHz Clock

VIN = 20 V

L = 2.2 uH

ILOAD = 3 A

Figure 10-13 Synchronizing to External 2.1-MHz Clock