The Introduction of The Sync Pin of CHB150W12 & CHB200W12

July 08, 2022

In some applications, different supply voltages would be applied for powering different types of function in a system. For example, a modern telecom system may use at least two supply rails: one is to power the telecom device, and the other one with the lower supply voltage is to power the microprocessor. These supply voltages may be generated by voltage regulators or DC-DC converters. If the system has multiple DC-DC converters for the different voltage supply rails, it will require a mechanism to minimize the switching noise distributed in the power distribution network of the system. This ripple & noise is usually reduced by adding the external decoupling capacitors at the input and output sides of the DC-DC converters. However, different switching frequencies of the DC-DC converters may bring the additional challenge to solve the EMI issue for the entire power system. In that case, the Sync Pin would be helpful to solve the problem.

Fig1. Typical power system with multiple converters

The switching frequency of CHB150W12 & CHB200W12 series can be synchronized with frequency of an external clock by giving a narrow pulse to the DC-DC converter via the Sync pin. The setup for the Sync function is shown as below:

Fig2. Recommended synchronization circuit for a single converter

Fig3. External synchronizing signal

The specifications of synchronization signal are the same for CHB150W12 and CHB200W12 series. In addition, the signal should be a TTL (Transistor-Transistor Logic) compatible signal with a maximum amplitude of 5.6V to prevent damage to the input pin of synchronization.

Note:

The frequency of the external clock must be between 530KHz~630KHz.

The pulse width of the external clock must be between 75ns ~ 120ns.

The voltage at the Sync pin must be driven to exceed 3.5V ~ 4.5V level.

If the external clock frequency is less than the switching frequency of CHB150W12 and CHB200W12, the module will ignore the pulse from the sync pin.

We could find that the original switching frequency of CHB150W12 and CHB200W12 is 480Khz from the waveform (Fig 4). After giving the external signal through sync pin, the PWM waveform is synchronized to be 630Khz. Moreover, it shows the output voltage ripple and Input current ripple could be synchronized as well (Fig 5 & 6).

Fig 4. Waveform with original 480KHz before giving the external signal

CH1: High-side PWM (Yellow) CH2: Low-side PWM (Red) CH3: Sync. signal (Blue)

Fig 5. Waveform after giving the 630KHz external signal

Fig 6. Waveform after giving the 630KHz external signal

The following block diagram (Fig7.) shows two DC-DC converters that have the sync function. They are on the same input bus and a signal would come from an external source of signal to synchronize both converters with the same switching frequency.

Fig 7. Two or multiple converters synchronization

CH1: PWM of Module1 CH2: PWM of Module2 CH3: Sync. signal	CH1: PWM of Module1 CH2: PWM of Module2 CH3: Sync. signal
CH1: PWM of Module1 CH2: PWM of Module2 CH3: Sync. signal CH4: Input current ripple	CH1: PWM of Module1 CH2: PWM of Module2 CH3: Sync. signal CH4: Input current ripple

According to the waveforms above, while the trigger is set to the PWM of Module 1 on the oscilloscope, the waveform of PWM is clearly shown. Furthermore, the persistence setting makes the waveform of PWM of Module 2 blurry, meaning the switching frequency is not completely the same as the that of Module 1. After the synchronization with 630KHz, the PWM waveform of converter 2 is clearly shown as well. Both Modules could operate at the same frequency and turn on their switches at the same time.

Via the brief demonstration of synchronizing single and two converters, technically speaking, the process of synchronization not only solves the problem of interference resulted from different switching frequency in a system but also reduces the input ripple current and output ripple voltage on paralleling more modules. This is like the concept of multi-phase interleaving.

Cincon provides CHB150W12 and CHB200W12 DC-DC converter series which could offer the function of synchronizing the switching frequency. Through an external signal, these converters could be synchronized with the same switching frequency and the input ripple current and output ripple voltage could be moderated. For more information, please check the product page or contact Cincon for support.

Product Page: CHB150W12   CHB200W12

E-mail: sales@cincon.com.tw