Multi-Channel Parallel Operation of High-Side and Low-Side Drivers

Application Notes2026-07-23

Author: Jason Chen
Corresponding Author: Cherry Cheng
Reviews: Hua Xiang, Yami Xi

ABSTRACT

High-side and low-side drivers that integrate multiple protection and diagnostic functions are widely used in automotive electronics and industrial control as replacements for traditional discrete MOSFET solutions. They are capable of adapting to various application scenarios commonly found in different systems, including resistive load heating, capacitive load fast startup, and inductive load turn-off clamping. For different systems, in multi-channel applications, the load currents of different channels often exhibit certain variations. When the current requirement of a particular channel exceeds the maximum load capability of a single channel of the driver, the system will fail to operate properly. One feasible solution is to parallel multiple channels of a multi-channel high-side driver to increase the load current capability. This application note will provide a detailed introduction to the key considerations and limitations that need to be taken into account in channel-parallel applications of high-side drivers.

1 Introduction to Multi-Channel Parallel Operation

In practical applications, when multi-channel high-side and low-side drivers operate at room temperature, the current capability of a single channel is typically sufficient to meet load requirements and drive the load stably without triggering the chip's thermal shutdown protection. However, when the ambient temperature rises, the load current required remains unchanged, but the driver's on-resistance increases with temperature. This physical characteristic leads to increased power dissipation, such that a load current that is acceptable at room temperature may exceed the thermal shutdown threshold at high temperatures due to intensified self-heating of the chip.

One effective way to address this issue is to add an external heatsink to dissipate the heat from the power device in a timely manner, ensuring that the overall junction temperature of the chip operates below the thermal shutdown protection threshold. However, the introduction of an external heatsink undoubtedly increases system cost and layout design complexity. In contrast, multi-channel parallel operation reduces the on-resistance to lower the power dissipation during normal driving, thereby effectively controlling temperature rise and allowing the chip to operate stably within the over-temperature protection threshold even at higher ambient temperatures. SG Micro Corp offers a variety of high-side and low-side driver products that can be used for channel paralleling, with representative models listed in Table 1.

These multi-channel high-side and low-side drivers are specifically designed for automotive systems and industrial applications, integrating short-circuit protection, over-temperature protection, over-voltage clamping, and open-circuit diagnostics, as well as internally and externally configurable current limiting. Among them, the high-side drivers also integrate high-precision current sensing circuits. This family of devices supports multiple load driving modes: all channels can be paralleled to drive a single high-current load, or partially paralleled to handle medium-current loads, or used as independent single channels to drive lighter loads with lower current requirements. Parallel channel output is achieved by connecting multiple power MOSFETs integrated within a single device in parallel to provide higher current to the load. In this configuration, the load current, originally borne by a single channel, is shared among the paralleled channels, with the theoretical current carried by each paralleled channel equal to the total load current divided by the number of paralleled channels. This parallel configuration enables these high-side and low-side drivers to drive loads that exceed the capability of a single channel, such as high-power halogen lamps, solenoids, electromagnetic valves, and motors.

2 Current and Voltage Output Relationship in Parallel Configuration

When multi-channel high-side and low-side drivers operate in parallel, the voltage drop (V_DS) from the supply pin V_CC to the output pin OUT is identical for all channels. For a high-side driver, the voltage drop is (V_CC − V_OUT); for a low-side driver, it is (V_DRAIN – V_SOURCE). The total output current after paralleling multiple channels equals the sum of the currents from each channel, and the total resistance equals the parallel equivalent of the on-resistances of all channels. Figure 1 illustrates the connection scheme for high-side and low-side drivers with n channels in parallel, showing the V_CC node and the V_OUT node connections for each channel. The upper portion of the figure shows the on-resistance R_ON(x) and corresponding current for each of the n independent channels, while the lower portion shows the equivalent on-resistance R_ON(EQ) and total output current I_OUT after paralleling.

Under ideal conditions, when multiple channels are used in parallel, the load current is evenly distributed among the channels, and the expected total output current I_OUT is n times that of a single channel. This requires the channels of the device to have highly consistent on-resistance. In actual manufacturing, due to process variations and bond-wire length differences within the same device, there are certain deviations in on-resistance among channels, resulting in uneven distribution of total output current across the paralleled channels. Within a single device, process variation can reach up to 10%. Taking SG Micro Corp's quad-channel high-side driver SGM42214xQ as an example, mass production test data shows that the single-channel on-resistance has a minimum value of 143mΩ, a typical value of 150mΩ, and a maximum value of 164mΩ, indicating a certain degree of manufacturing process variation.

Taking a 12V system application with a total load current of 6A required at +85°C ambient temperature as an example, the quad-channel high-side driver SGM42214xQ from SG Micro Corp can be selected for 4-channel parallel driving. Referring to the SGM42214xQ Datasheet^[1], the typical single-channel on-resistance at +25°C ambient temperature is 150mΩ; at +125°C ambient temperature (V_CC > 13.5V), the maximum on-resistance is 270mΩ. The junction-to-ambient thermal resistance parameter θ_JA is 25.7°C/W. With 4 channels in parallel, each channel needs to drive a typical current of 1.5A to meet the 6A total load current requirement. Theoretically, the maximum power dissipation generated during normal operation with a 6A load current is:

The temperature rise generated by the paralleled power devices is:

The junction temperature at +85°C ambient temperature is:

Since the on-resistance R_ON among channels can have a maximum deviation of ±10%, the actual load current per channel may vary between 1.35A and 1.65A. This current variation among channels remains within the current capability and temperature rise limits specified in the device datasheet. As shown in Figure 2, Probe 1 measures the output voltage, Probe 3 measures the supply voltage, and Probe 4 is set to 1A/DIV, measuring a total load current of 6A. As shown in Figure 3, Channel 2 (Current Probe 1) measures a maximum single-channel current of 1.6A, while Channel 4 (Current Probe 2) measures a minimum single-channel current of 1.41A. The measurement results indicate that the current and voltage of each channel are within the design target range.

3 Design Considerations for Parallel Channel Applications

In multi-channel parallel applications, the protection and diagnostic functions of the paralleled configuration are approximately equivalent to those of a single channel. To ensure synchronous output of all paralleled channels, for direct PWM-controlled high-side and low-side drivers, the input pins INx of all parallel channels must be connected together, and the output pins OUTx should be paralleled and connected close to the load to reduce parasitic inductance effects. Additionally, design considerations must fully account for parameter deviations among channels, including on-resistance, current sensing gain K, and inductive load turn-off clamping. Figure 4 illustrates the input and output connection scheme for multi-channel parallel operation. For SPI-controlled switches, it is necessary to ensure synchronous setting of the switch commands for the paralleled channels. Furthermore, the STx pins (with single-channel fault status indication function) should be connected in parallel and pulled up externally before being fed back to the microcontroller. For parallel driving, the CSx pins (with multi-channel independent current sensing capability) should also be connected in parallel to the sense resistor R_SENSE for total load current detection.

Figure 5 shows the switching delay measurement results between output channels when multiple inputs are shorted together in direct-drive mode for the SGM42214xQ. Since the internal four channels share the same charge pump circuit for driving, the switching delay error among channels is only from the internal clock, with delay times on the order of microseconds. Measurements show that the output delay between Channel 2 and Channel 4 is 0.2μs. Compared to the tens-of-microseconds rise/fall times of the switching transitions, this delay has essentially no impact on parallel-driving load applications. Similarly, Figure 6 shows the synchronous command settings for parallel driving channels in SPI-controlled mode, referencing the SGM42404A/B Datasheet^[2]. Figure 7 shows the measured output delay times among individual channels during multi-channel synchronous turn-on. The measurement shows that the output delay between Channel 2 and Channel 4 is 3.6ns, which meets the allowable delay error range for synchronous switching among channels.

4 Impact on Functional Parameters in Parallel Channel Applications

The protection function parameters in multi-channel parallel applications are essentially consistent with those of single-channel independent driving. Table 2 summarizes the characteristics and considerations for high-side and low-side drivers in parallel applications, and Table 3 summarizes the differences in diagnostic functions between single-channel and parallel-channel applications.

It should be noted that:

1) For devices that perform current sensing through channel-switching polling (e.g., SGM42214xQ), in parallel applications, the current sensing reports only the current flowing through a single output channel, and the total current sensing value equals the sum of the current sensing readings from each channel. The CS pin application diagram is shown in Figure 8. The CS pin voltage that can be detected by the microcontroller is:

2) For devices with independent current sensing for each channel (e.g., SGM42203/42203Q), in parallel applications, all CS pins can be shorted together and connected to the sense resistor R_SENSE for total current detection. The CS pin application diagram is shown in Figure 9. The CS pin voltage that can be detected by the microcontroller is:

In multi-channel high-side and low-side driver parallel applications driving inductive loads, the back-EMF generated during turn-off due to the inductive current's inability to change instantaneously must be safely clamped within the device's safe voltage capability. Each channel internally integrates drain-source voltage clamp protection, but in parallel applications, the clamp voltage does not multiply and remains the same as for a single channel. When turning off high-current, high-inductance loads, the demagnetization energy E_ASto be dissipated is not evenly distributed among all channels. Due to device process variations, there are also certain deviations in clamp voltage among channels. In the worst-case scenario, the channel with the lower clamp voltage will be the first to activate clamp protection and conduct slightly, causing all demagnetization energy to flow through that single channel, and the resulting transient stress may damage that channel. If the demagnetization energy required for turning off a parallel-driven inductive load (E_AS = 1/2 × L × I²) is estimated to be higher than the turn-off demagnetization energy that a single channel can withstand, SG Micro Corp recommends referring to the application notes in the datasheet and adding an external clamp circuit to dissipate the excess demagnetization energy during design.

The fault diagnostic functions integrated in high-side and low-side drivers are fed back to the microcontroller through pins such as nFAULT, STATUS, CS, and SDO. The diagnosable fault types include: open-circuit detection, output short to supply or ground, over-current, overload, thermal shutdown, etc. When channels are paralleled with outputs shorted together, for devices that use analog current-sensing CS pins for fault reporting, any single channel can be selected via logic input pins to feedback load current status and device fault diagnostic information. Referring to the single-channel diagnostics and multi-channel parallel application diagnostics summarized in Table 3, in most cases when channels are paralleled, faults are not distinguished by channel and are reported through a single channel. Notably, in cases such as overload thermal restart or thermal shutdown protection in multi-channel driving, the fault can be identified through the corresponding channel's fault reporting. This is because process variations cause parameters such as current limit and on-resistance among paralleled channels to not be perfectly consistent. Once one channel reaches its current limit threshold, or its power dissipation triggers the thermal shutdown threshold and causes shutdown, that channel's current is forcibly redistributed to the other paralleled channels, which may subsequently trigger overload thermal shutdown in those channels as well.

5 Conclusion

By paralleling the outputs of multi-channel high-side and low-side drivers, output currents exceeding the maximum capability of a single channel can be achieved. From the perspective of multi-channel parallel applications, this article has introduced the current and voltage relationships of inputs and outputs, and elaborated on design considerations, functional parameter impacts, and differences in diagnostic fault reporting for parallel channel applications. In practical applications, to ensure system stability, reliability, and necessary safety margins, full consideration must be given during design to parameter deviations among channels and to all specifications outlined in the device datasheets.