New Industry Products

Nano Pulse Technology for Primary DC/DC Converter Design: Reducing Application PCB Size and Cost

July 11, 2022 by ROHM Semiconductor

The industrial and consumer market is requiring increased power density for DC/DC converters that have high step-down ratios and use high technological innovation. Different challenges need to be overcome in semiconductor products to fulfill these requirements. ROHM successfully developed the BD9F500QUZ with several additional features such as Nano Pulse Technology and increased peak current capabilities.

ROHM’s synchronous primary DC/DC buck converter IC BD9F500QUZ utilizes Nano Pulse Technology and is ideal for applications where high-voltage conversion ratio is required with a single IC. The input voltage range is 4.5 V to 36 V and output voltage range is 0.6 V to 14 V. The BD9F500QUZ moreover is suitable for applications that require high peak currents during start-up or continuous operation. Maximum average current of 5A with maximum peak current of 8.25 A is possible while maintaining acceptable temperature behavior. The overall application PCB size is compact since the BD9F500QUZ has a small VMMP16LZ3030 package and is ideal for a wide range of industrial and consumer applications.

Nano pulse control™ technology that is implemented in the BD9F500QUZ refers to the ultra-high-speed pulse control allowing high voltage conversion ratio using a single IC in a small package and achieving both high efficiency and stable output voltages for high switching frequencies. Nano pulse control™ technology developed by ROHM ensures stable output voltages are achieved above conventional technology for converter switching frequencies (fSW) up to 2.2 MHz and for on-time (TON) down to 48 ns for the BD9F500QUZ. The advantage of using higher converter switching frequencies is the reduced inductor size in application and together with the small VMMP16LZ3030 package this reduces overall PCB size at application level. In an application example, a conversion from 24 V input to 1 V output is shown with the converter running at 735kHz. This is equivalent to a cycle period (TSW = 1/fSW) of approximately 1.36 µs and the on time (TON) of the converter becomes 57ns.

 

Figure 1. Nano pulse technology for VIN = 24V, VOUT = 1V, TON pulse width = 57ns and switching frequency = 735kHz. Image used courtesy of Bodo’s Power Systems

 

The BD9F500QUZ is a synchronous buck converter that adopts voltage feedback allowing an output voltage range of 0.6V to 14V. It supports a large input voltage range of 4.5V to 36V and the high and low side FETs can handle average loads up to 5A and peak current loads of 8.25A.

A wide range of applications are supported such as:

  1. Power supply for ASIC/SoC/FPGA
  2. Printer applications
  3. OA equipment
  4. Laptop, PC, LCD TV
  5. USB Type-C applications

 

SEL1 pin

SEL2 pin

Switching Frequency

Maximum Output Current

Operation Mode

High Side OCP

Low Side OCP (LLM)

Low Side OCP (Fixed PWM mode)

GND

GND

1MHz

5A

Light Load Mode (LLM)

IHOCP = 8.25A

ILOCP = 6.7A

IROCP = 4.2A

GND

OPEN

Fixed PWM Mode

VREG

GND

3A

Light Load Mode (LLM)

IHOCP = 5A

ILOCP = 4A

IROCP = 2.5A

VREG

OPEN

Fixed PWM Mode

OPEN

GND

600kHz

5A

Light Load Mode (LLM)

IHOCP = 8.25A

ILOCP = 6.7A

IROCP = 4.2A

OPEN

OPEN

Fixed PWM Mode

GND

VREG

3A

Light Load Mode (LLM)

IHOCP = 5A

ILOCP = 4A

IROCP = 2.5A

OPEN

VREG

Fixed PWM Mode

VREG

VREG

2.2MHz

3A

Fixed PWM Mode

IHOCP = 5A

ILOCP = 4A

IROCP = 2.5A

Table 1. Setting for output current and OCP.

 

For many industrial applications, peak currents can easily exceed the average current during start-up of the application, during dynamic load transients or during short circuit conditions of output. The integrated MOSFETs in the BD9F500QUZ have sufficient margin to handle these peak currents because of an integrated advanced Over Current Protection (OCP) mechanism. The current is monitored in both low side and high side FETs for each switching cycle. Figure 2 shows an overview of the different signals for the OCP mechanism. When the peak current in the high side FET exceeds the high OCP threshold level (IHOCP), the high side FET is then temporarily switched off. Now the low side FET is switched on and inductor current begins to fall. When the current in the low side FET reaches the low OCP threshold level (ILOCP), the high side is temporarily switched on again. Every time the low OCP threshold level (ILOCP) is reached and when VFB level is below 90%, then an OCP count is registered.

 

Image used courtesy of Bodo’s Power Systems

 

Figure 2. Over Current Protection (OCP) mechanism and measurement waveform for OCP count greater than 128. Image used courtesy of Bodo’s Power Systems

 

The device continues this cycle switching operation if the OCP count of 128 is not exceeded and the inductor current maintains a constant current for 128 counts even after the high OCP threshold level (IHOCP) has occurred. Consequently, in the case where such short current peaks occur, then constant current is maintained to the output load once the OCP count remains less than 128. If the OCP count is greater than 128 then the inductor current falls further below ILOCP and the converter stops switching operation for a duration as indicated in Figure 2.

With the BD9F500QUZ, the maximum output current of 3A and 5A and the OCP levels for both high side FET (IHOCP) and low side FET (ILOCP, IROCP) can be set via the SEL1 and SEL2 pins. The settings for output current together with the high side and low side OCP settings are shown in Table 1.

For average output currents of up to 5A, the high OCP threshold level (IHOCP) can be set to 8.25A for the high side FET. The low OCP threshold level (ILOCP) can be set to 6.7A or 4A for low side FET depending upon operation mode namely Light Load Mode or fixed PWM mode. Peak currents of up to 8.25 A can be handled by the high side FET and output current is maintained to the load during these conditions on the condition that the low side OCP count remains less than 128. The complete system solution using BD9F500QUZ together with external input/output capacitors and inductor offers a considerable reduction in PCB size compared to existing solutions. Furthermore, high efficiency over the complete load current range is achieved with a small VMMP16LZ3030 package for both fixed PWM mode and light load mode (LLM). A summary of efficiency and thermal performance is shown in Figure 3.

 

Figure 3. Efficiency for PWM Mode, Light Load Mode (LLM) and thermal behavior of VMMP16LZ3030 package for parameter settings of VIN = 24V, VOUT = 1V with average output current load of 3A. Image used courtesy of Bodo’s Power Systems

 

Conclusion

The BD9F500QUZ adopts Nano Pulse Control technology ensuring stable output voltage over the complete load range with fast transient response. It has the advantage of high conversion ratios at switching frequencies up to 2.2MHz. High efficiency with good thermal performance is achieved with a small package (3mm x 3mm x 0.4mm). The high-power density device has an increased peak current capability that easily exceeds the effective rated current capacity of conventional DC/DC converters for a similar PCB size. Therefore, an elegant solution is realized with the BD9F500QUZ as DC/DC converter which reduces the overall size and cost of the system application.

 

This article was co-authored by Thady Bruton and Muzaffer Albayrak of ROHM Semiconductor and originally appeared in Bodo’s Power Systems magazine.