SN6507 datasheet(17/44 Pages) TI

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switch. The duty cycle is fixed with 70 ns deadtime to avoid shoot-through. The duty cycle is changeable if duty

cycle feature is enabled. Please refer to Section 8.3.3.

SN6507-Q1 has a wide switching frequency range from 100 kHz up to 2 MHz, which is pin-programmable

through a resistor (RCLK) to GND. Below table lists the value of RCLK to achieve certain operating frequencies

(fSW). The choice of switching frequency is a trade-off between power efficiency and size of capacitive and

inductive components. For example, when operating at higher switching frequency, the size of the transformer

and inductor is reduced, resulting in a smaller design footprint and lower cost. However, higher frequency

increases switching losses and consequently degrades the overall power supply efficiency.

Table 8-1. Recommended 1% RCLK values and fSW Look-up Table

RCLK

fSW (Typical)

111 kΩ

105 kHz

21 kΩ

523 kHz

9.6 kΩ

1.07 MHz

4.1 kΩ

2.13 MHz

0 kΩ (Short to GND)

Default (1 MHz)

Figure 8-6 can also be used to estimate the programmable switching frequency, fSW, using an external resistor

value, RCLK, where RCLK is in kΩ and fSW is in kHz:

RCLK (k)

100

1000

8 10

70 90 110

500

2000

Figure 8-6. Approximate SN6507-Q1 Switching Frequency, FSW, for RCLK Range

If CLK pin is shorted to GND, the part switches at its default frequency, FSW. CLK pin floating is not a valid state

of operation and will cause the part to stop switching until an external clock signal is present.

8.3.4 Spread Spectrum Clocking

Radiated emissions is an important concern in high current switching power supplies. Due to the periodicity of

the digital clock signals, the energy concentrates in one particular frequency and also in its odds harmonics,

causing EMI issues. SN6507-Q1 implements Spread spectrum clocking (SSC) to reduce the radiated emissions

of digital clock signals. The device modulates its internal clock in such a way that the emitting energy is spread

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SN6507-Q1

SLLSFM1 – SEPTEMBER 2022

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