The switching frequency of the TPS2583xA-Q1 can be programmed by the resistor R_T from the RT/SYNC pin and GND pin. To determine the RT resistance, for a given switching frequency, use Equation 3:

Equation 3.

Figure 10-6 RT Set Resistor vs Switching Frequency

Table 10-1 lists typical RT resistors values.

TPS2583xA-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 2.0 V (minimum) 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. #SNVSAH23098 shows the device synchronized to an external clock.

Figure 10-7 Synchronize to External Clock

In order to avoid AM radio frequency band and maintain proper regulation when minimum ON-time or minimum OFF-time is reached, the TPS2583xA-Q1 implements a frequency foldback scheme depending on VIN voltage, refer to Figure 8-11.

• When 8 V < VIN ≤ 19 V, the switching frequency of TPS2583xA-Q1 is determined by R_T resistor or external sync clock.
• When VIN ≤ 8 V, the switching frequency of TPS2583xA-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 TPS2583xA-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 = 8.66 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 = 3.3 uH

ILOAD = 3 A

Figure 10-8 Switching Frequency When R_T = 8.66 kΩ

VIN = 20 V

L = 3.3 uH

ILOAD = 3 A

Figure 10-10 Switching Frequency When R_T = 8.66 kΩ

VIN = 13.5 V

L = 3.3 uH

ILOAD = 3 A

Figure 10-12 Synchronizing to External 2.1-MHz Clock

VIN = 13.5 V

L = 3.3 uH

ILOAD = 3 A

Figure 10-9 Switching Frequency When R_T = 8.66 kΩ

VIN = 7.5 V

L = 3.3 uH

ILOAD = 3 A

Figure 10-11 Synchronizing to External 2.1-MHz Clock

VIN = 20 V

L = 3.3 uH

ILOAD = 3 A

Figure 10-13 Synchronizing to External 2.1-MHz Clock