SLUAAY9 August   2024 TPS543320 , TPS543620 , TPS543820

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Choosing Component Values
    1. 2.1 Capacitor
    2. 2.2 Resistor
    3. 2.3 Clock Signal
    4. 2.4 Schottky Diode
  6. 3Results
    1. 3.1 Waveforms
    2. 3.2 Bill of Materials
  7. 4Summary
  8. 5References

1 Introduction

Slight variations in switching frequency when using multiple DC/DC converters can introduce additional challenges to the system design that can be mitigated by synchronizing the switching frequency to a common clock generator. For example, switching frequency synchronization allows users to filter out a predictable frequency band to eliminate potential adverse effects to other components in the system. Users can also have multiple DC/DC converters in a design switch at the same frequency but in different phases, minimizing input voltage, current ripple and EMI effects.

The TPS543620 family of devices are high-performance synchronous DC/DC converters that utilize the internally-compensated, fixed-frequency Advanced Current Control mode control topology and deliver high efficiency in a small 2.5mm x 3mm HotRod™ VQFN package. These devices are available in a 3A, 6A and 8A version, and can operate from 500kHz to 2.2MHz. The devices can also be synchronized to an external clock directly connected to the SYNC/FSEL pin.

To enable external clock synchronization, apply a square wave clock signal to the SYNC/FSEL pin with a duty cycle from 20% to 80%. The clock can either be applied before the device starts up or during operation. If the clock is to be applied before the device starts, then a resistor between SYNC/FSEL and AGND is not needed. In the case that the device starts up before an external clock signal is applied, then the internal PWM oscillator frequency is set by the RFSEL resistor. There are five possible frequency options for the TPS543620 and the corresponding programming resistor values are listed in Table 1-1.

Table 1-1 TPS543620 Switching Frequency Selection
RFSEL ALLOWED NOMINAL RANGE (1%) (kΩ) RECOMMENDED E96 STANDARD VALUE (1%) (kΩ) RECOMMENDED E12 STANDARD VALUE (1%) (kΩ) Fsw (kHz)
>=24.0 24.3 27

500
17.4-18.0 17.4 18

750
11.8-12.1 11.8 12

1000
8.06-8.25 8.06 8.2

1500
<=5.11 4.99 4.7

2200

The device maintains this switching frequency until the clock signal is applied, at which point the device begins synchronizing to this clock after counting four consecutive switching cycles. This application note assumes that the clock is not present before the device starts, necessitating the need for a high impedance design to verify proper detection of the RFSEL resistor.

AC coupling refers to a method used in electronics circuits where a capacitor is added in series on the signal line, functioning as a high-pass filter that allows AC signals to pass through while blocking DC signals. In a DC/DC converter clock synchronization application, a clock signal functions as a DC signal that oscillates between a high and low state at a constant frequency. Utilizing an AC coupled circuit effectively isolates the clock generator from the rest of the components down the path to verify proper detection of the RFSEL value and regulates the clock signal to be within the necessary voltage values of the SYNC/FSEL pin. The clock synchronization high-level input voltage threshold of the device is 1.8V and the absolute minimum input voltage on the SYNC/FSEL pin is -0.3V.