Revolutionary 700 V high-frequency, high- and low-side drivers enable ultra-high power density

ON semiconductor‘s NCP51530 is a 700 V high- and low-side driver for AC-DC power supplies and inverters that provides best-in-class propagation delay, low quiescent current and switching current for high frequency operation. The NCP51530 has the industry’s lowest level drift losses, enabling power supplies to operate efficiently at high frequencies. This article will compare the NCP 51530 to two industry-standard devices. Calculation of losses in the NCP 51530 for Active Clamp Flyback (ACF) USB PD Adapters. The actual thermal performance of the NCP 51530 compared to two competing devices for ACF applications is then given.Next, compare the energy efficiency data of the ACF board using NCP 51530 with the

Summary

ON Semiconductor’s NCP51530 is a 700 V high- and low-side driver for AC-DC power supplies and inverters that provides best-in-class propagation delay, low quiescent current and switching current for high frequency operation. The NCP51530 has the industry’s lowest level drift losses, enabling power supplies to operate efficiently at high frequencies. This article will compare the NCP 51530 to two industry-standard devices. Calculation of losses in the NCP 51530 for Active Clamp Flyback (ACF) USB PD Adapters. The actual thermal performance of the NCP 51530 compared to two competing devices for ACF applications is then given. The energy efficiency data for the ACF board using the NCP 51530 is then compared with the energy efficiency data for the ACF board using the two competing devices.

foreword

To make modern power supplies more compact and efficient, power supply designers are increasingly opting for high frequency applications. The high frequency operation of the switching power supply can reduce the size of the transformer, thereby increasing the power density of the power supply. High frequency operation also helps to improve the electromagnetic interference (EMI) signal of the power supply, reducing the EMI component count. As a result, power supply designers around the world are investigating high frequency applications.

However, there are some hurdles in realizing high-frequency power supplies. Power switches, transformer core materials, leakage losses, and switching losses are some of the obstacles hindering the large-scale application of high-frequency power supplies. With the advent of Gallium Nitride (GaN)/Silicon Carbide (SiC) technology and the continuous development of MOSFET technology, power switches seem to be starting to be suitable for high frequency power supplies. Likewise, transformer core material manufacturers are working tirelessly to innovate high-frequency core materials.

Zero-voltage switching (ZVS) topologies can reduce switching losses associated with power switching. Commonly used ZVS topologies such as LLC, half-bridge converter, full-bridge converter, active clamp flyback, dual switch forward converter, etc. Low-side and high-side drivers are required for buffering and level shifting functions. These devices can drive the gate of a high-side MOSFET whose source node is a dynamically changing node.

There are inherent losses associated with power switch drivers. In power switches with totem pole structures, such as LLC, half/full bridge converters, etc., the level shift loss of the high-side driver is large. The higher the frequency, the more severe these losses are.


NCP51530 Features

ON Semiconductor’s NCP51530[1] are 700 V, high and low side drivers for AC-DC power supplies and inverters that provide best-in-class propagation delay, low quiescent current and switching current for high frequency operation. The NCP51530 has the industry’s lowest level drift loss. The device thus enables the power supply to operate efficiently at high frequencies.

The NCP51530 has two versions, A/B. The NCP51530A has a typical 50 ns propagation delay, while the NCP51530B has a 25 ns propagation delay. The NCP51530 is available in SOIC8 and DFN10 packages. Its SOIC8 package is pin-to-pin compatible with industry standard solutions.

The NCP51530 has two independent input pins: HIN and LIN, enabling it to be used in a variety of different applications.

The device also includes features that, in the case of floating inputs, the logic is still delimited. The driver input is compatible with CMOS and TTL logic, so it is easy to interface with analog and digital controllers. The NCP51530 features high- and low-side drive undervoltage lockout to ensure that the correct VCCand VBoperate at the voltage level. The output stage of the NCP51530 has 3.5A/3A source/sink capability and can efficiently charge and discharge a 1 nF load in 10 ns.

NCP51530 Active Clamp Flyback Applications

Active clamp flyback (ACF) is a variant of the classic flyback topology that achieves ZVS by utilizing energy stored in parasitic devices rather than by dissipating power in snubber circuits. The waveforms produced by active clamps are generally free of spikes and therefore have better immunity to electromagnetic interference (EMI) than conventional techniques. The ZVS feature enables power converters to operate at high frequencies while achieving high energy efficiency.

ON Semiconductor’s NCP1568[2]are highly integrated AC-DC pulse width modulation (PWM) controllers for implementing active clamp flyback topologies. The NCP 1568 uses a proprietary frequency conversion algorithm to achieve zero-voltage switching (ZVS) of superjunction or GaN FETs under various linear, load and output conditions. The ZVS feature increases the power density of the power converter by increasing the operating frequency while achieving high energy efficiency.

To minimize power loss in ACF applications, when the load and input voltage change, the operating frequency needs to be changed to keep additional circulating currents to a minimum. For superjunction FETs, the negative current required for ZVS is typically −0.5A. The negative magnetizing current is held digitally relatively constant by adjusting the frequency of the oscillator until the fall time of the SW node is modulated to a predetermined dead time under linear and load conditions. The time base is established in the NCP1568 and the error signal is accumulated based on the time required to convert and achieve ZVS. If the switching node transitions are fast and ZVS occurs before the reference time, there is more than enough energy to quickly reset the node, so the operating frequency should be reduced or the off time should be reduced. If the switching node ZVS happens exactly at the reference time, no frequency adjustment is required. If ZVS occurs after the reference time, the frequency is too high and needs to be lowered to ensure good ZVS.

Revolutionary 700 V high-frequency, high- and low-side drivers enable ultra-high power density

Figure 1 ACF adopts NCP51530 and NCP1568

As expected, the algorithm works more efficiently in high-side drivers with fast propagation delays. Drivers with slower propagation delays using this algorithm will result in lower operating frequencies than drivers with faster propagation delays, making the overall system less energy efficient and more costly. The NCP 51530 is the fastest high- and low-side driver in the industry and perfectly implements this function.

The top-level schematic of the ACF board using the NCP1568 and NCP51530 is shown in Figure 1. This schematic is for a 60W, universal input, 20 V output power supply application. The power supply uses ON Semiconductor’s NCP1568 PWM controller, NCP 51530 high and low side drivers, NCP 4305 synchronous rectification (SR) controller and FDMS 86202 SR FET. This is variable frequency and the ACF operates from 200 kHz to 400 kHz. A typical ACF waveform is shown in Figure 2.

Revolutionary 700 V high-frequency, high- and low-side drivers enable ultra-high power densityRevolutionary 700 V high-frequency, high- and low-side drivers enable ultra-high power density

Figure 2. Active Clamp Flyback Mode

Calculate the loss of NCP51530

In this part, we use NCP1568 to calculate the power consumption of NCP51530 in ACF application.The total power loss of the drive can be roughly divided into static power loss and dynamic power loss[4]. Static power loss is caused by the bias current required for device operation. Dynamic losses are due to the switching characteristics of the device. The dynamic loss can be further divided into the charge-discharge loss of the external FET gate and the charge-discharge loss of the level-shift capacitor.

The total power dissipation of the NCP51530 can be calculated step by step as follows.

1. The static power loss of the device (excluding the driver) when switching at the appropriate frequency.

Revolutionary 700 V high-frequency, high- and low-side drivers enable ultra-high power densityRevolutionary 700 V high-frequency, high- and low-side drivers enable ultra-high power density

Revolutionary 700 V high-frequency, high- and low-side drivers enable ultra-high power density

IBOis the operating current of the high-side driver

ICCOis the operating current of the low-side driver

2. Power loss driving external FET

This loss is due to the charging and discharging of the gate capacitor of the external FET. Because in this ACF application, only one external FET is driven by the NCP 51530, we only consider the power loss driving one MOSFET.

If the NCP51530 is used to drive the high and low side FETs, the charge and discharge power losses of the gates of the two external MOSFETs must be included.

Revolutionary 700 V high-frequency, high- and low-side drivers enable ultra-high power densityRevolutionary 700 V high-frequency, high- and low-side drivers enable ultra-high power densityf

Revolutionary 700 V high-frequency, high- and low-side drivers enable ultra-high power density

Qgs is the gate-source charge of the MOSFET

Vbootis the high-side bias supply voltage

f is the operating frequency

3. Level drift loss[4]

When the high-side switch turns off, it causes current to flow into the level-shift circuit, charging the ldmos1 capacitor. This current flows from the high voltage bus through the power devices and bootstrap capacitors. On the other hand, when the high-side switch is turned on, it causes the current to flow from VCCFlow through the bootstrap diode into the level-shift circuit.

Revolutionary 700 V high-frequency, high- and low-side drivers enable ultra-high power densityRevolutionary 700 V high-frequency, high- and low-side drivers enable ultra-high power density


Revolutionary 700 V high-frequency, high- and low-side drivers enable ultra-high power densityRevolutionary 700 V high-frequency, high- and low-side drivers enable ultra-high power density

Vsw is the rail voltage

Qlsis the substrate charge of the level-shift circuit

Vbootis the high-side bias voltage

f is the operating frequency

4. Charge and discharge losses of P-well capacitors[4]

In a half-bridge power circuit, the well capacitor is charged and discharged every time the switch node swings between the rail and ground levels. This charging current is provided by the high voltage rail. The discharge path for this current is through the low-side device and the epi resistor. Most of the losses occur outside the high- and low-side drivers because the epi resistance is much smaller than the internal device resistance. Therefore, these losses are not included in the losses inside the high and low drivers.

Revolutionary 700 V high-frequency, high- and low-side drivers enable ultra-high power densityRevolutionary 700 V high-frequency, high- and low-side drivers enable ultra-high power density


Revolutionary 700 V high-frequency, high- and low-side drivers enable ultra-high power densityRevolutionary 700 V high-frequency, high- and low-side drivers enable ultra-high power density

Vsw is the rail voltage

QCwell is the substrate charge of the capacitor well of the switch node

f is the operating frequency

5. Total Power Loss

The total power loss of the driver is the sum of drive loss, static loss, and level shift loss. It is not considered here due to the well capacitance CwellThe losses caused by the charging and discharging of the MOSFET, because most of the losses are inside the MOSFET, not the driver. But these losses affect system energy efficiency.

Revolutionary 700 V high-frequency, high- and low-side drivers enable ultra-high power density

Revolutionary 700 V high-frequency, high- and low-side drivers enable ultra-high power densityRevolutionary 700 V high-frequency, high- and low-side drivers enable ultra-high power density

6. Junction temperature rise

Revolutionary 700 V high-frequency, high- and low-side drivers enable ultra-high power density

Tj is the junction temperature

RθJA is the thermal resistance

P total is the total power loss of the device

Comparison with Competitive Devices

We selected two competitor devices for comparison, which are industry standard devices used in similar applications as the NCP51530 and in the same package as the NCP51530. Both were tested with the same active clamp flyback EVB setup as the NCP51530. Under exactly the same conditions, the thermal data of these three driver ICs were compared in pairs, and the energy efficiency of ACF boards using these three driver ICs were compared separately.

Thermal results

The NCP1568 implements ZVS under all conditions using a proprietary frequency conversion algorithm. As mentioned above, under the same load conditions, the different propagation delays of the three drivers result in different operating frequencies. For a fair comparison, this algorithm was not used when comparing the thermal performance of the three devices. The EVB was configured to operate at a constant frequency of 425 kHz. Thermal data was collected for the three devices under a 115 VAC input and 1A output load.

Table 1 shows the maximum and minimum temperatures for the drives in the ACF EVB. Figure 3, Figure 4, and Figure 5 show thermal images of the NCP51530, Competitor 1, and Competitor 2 running in the application, respectively. As can be seen from the thermal images, the NCP 51530 dissipates heat better than the two industry-standard competing devices. At an operating frequency of 425 kHz, the NCP51530 temperature is only around 50°C, and competing devices 1 and 2 exceed 90°C, and the performance difference will be more pronounced at higher operating frequencies. This is because the level-shift loss is one of the most important loss mechanisms in the high- and low-side drive loss mechanisms.

The excellent thermal properties of NCP 51530 make it suitable for high density boards. This result once again demonstrates that the NCP51530 is the industry’s best performing high and low side driver for high frequency applications.

Numbering

device

Maximum temperature (°C)

Average temperature (°C)

1

NCP51530

52.58

49.23

2

Competitor 1

95.02

83.22

3

Competitor 2

90.95

80.26

Table 1 Temperature data of three devices in ACF EVB

Revolutionary 700 V high-frequency, high- and low-side drivers enable ultra-high power density

Figure 3 Thermal image of ACF using NCP51530 C

Revolutionary 700 V high-frequency, high- and low-side drivers enable ultra-high power density

Figure 4 1C thermal image of ACF EVB using a competing device

Revolutionary 700 V high-frequency, high- and low-side drivers enable ultra-high power density

Figure 5 2C thermal image of ACF EVB using a competing device

Energy efficiency comparison:

We used the ZVS algorithm to collect energy efficiency data for the ACF boards of the three drivers described above at 115 VAC, 230 VAC inputs and 4 points of load (5 A, 1 A, 1.5 A, and 2 A). The data are shown in Table 2, Figure 7 and Figure 8.

The energy efficiency difference between the NCP51530 and competing devices is more than 1% at 40W load and more than 2% at lower load. Figures 7 and 8 demonstrate this well. At lower load points, the NCP1568 operates at higher frequencies, and as shown above, at higher frequencies the difference in losses between the NCP51530 and competing devices is greater. So in ACF EVB, the performance of NCP 51530 is better at lower load than at higher load.

This is due to a direct increase in energy efficiency due to level shift and reduced C-well charge-discharge losses. The effect of reducing the level drift loss can be seen directly in the thermal data. The combined effect of the level drift and the C-well charge and discharge loss improves the energy efficiency of the system.

Numbering

Output current (A)

NCP51530 (%)

Competitor 1(%)

Competitor 2 (%)

1

2

92.96

91.99

92.31

2

1.5

92.59

91.26

91.76

3

1

91.00

89.49

89.89

4

0.5

86.08

83.71

83.98

Table 2 C 115 VAC Energy Efficiency Data

Numbering

Output current (A)

NCP51530 (%)

Competitor 1(%)

Competitor 2 (%)

1

2

92.53

91.57

91.36

2

1.5

91.37

89.91

89.94

3

1

88.69

86.63

86.63

4

0.5

83.23

78.02

78.19

Table 3-230 VAC Energy Efficiency Data

Revolutionary 700 V high-frequency, high- and low-side drivers enable ultra-high power density

Competing Devices

Figure 6 115 VAC input, energy efficiency of NCP51530 compared to competing devices

Revolutionary 700 V high-frequency, high- and low-side drivers enable ultra-high power density

Competing Devices

Figure 7 230 VAC input, energy efficiency of NCP51530 compared to competing devices


Summarize:

Thermal and energy efficiency data show that the NCP51530 performs significantly better than the two industry-standard devices. In a thermal data comparison, under the same linear and load conditions, the NCP51530 tops out at 50°C, while competing devices exceed 90°C. At full load, the ACF board using the NCP51530 is about 1% more energy efficient than the ACF board using the two competing devices. The NCP51530 also features the industry’s fastest propagation delay, optimizing ACF operation.

The results show that the NCP51530 is a high-performance device suitable for high-frequency applications. The higher the frequency, the smaller the transformer, and therefore the higher the density of the power board designed. And the excellent thermal performance of NCP51530 enables it to be used in high density boards without increasing the thermal signal of the board.

The NCP51530 supports many high frequency topologies that previously required more expensive drive schemes (pulse transformers). As such, this is a game-changing device that helps bring high-frequency topologies and ultra-high-density designs to a market currently stalled by the lack of efficient high-side drivers.

The Links:   CXA-0538-A G190ETN020

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