When to choose a high side switch and when to choose a bottom side switch?

xutong

When to choose a high side switch and when to choose a bottom side switch? [Copy link]

When I look at the load switch again, I can't figure it out

What is the basis for choosing a high side or a low side?

Rohm's explanation is this:

https://www.rohm.com/electronics-basics/ipds/high-side-and-low-side-drive

Usage examples for high side and low side switches

IPDs incorporate a high side switch for the upper circuit and a low side switch for the lower circuit with respect to external loads, utilizing a circuit design optimized for each location.
As shown in the figure at left below, in a circuit where various loads are connected to a single power supply voltage, such as in a vehicle where the battery voltage is fixed and body connected to ground, the output can easily become grounded, making a high-side switch more suitable for detecting abnormal conditions such as ground faults.
Conversely , low side switches are ideal for circuits in which loads are placed at various power supply voltages as shown in the figure at right below. The low side switch operates by applying an input voltage to the gate and connecting the MOSFET Source to ground. This control scheme is the same as with single MOSFETs, making it easy to replace individual MOSFETs.

It's called How to Choose Between High-side and Low-side Switching

URL: https://www.elektormagazine.com/news/high-side-low-side-switching

The explanation given is that if you only need normally open or normally closed, choose the high side, and if you need PWM control, choose the low side.

Then I read TI's article, and his selection of high side and bottom side is as follows

Source: 11ways to protect your power path

Probably because the bottom edge has less protection, you guys buy the high edge

Then I went to see ST, whose bottom edge protection is very complete VNL5030 web page

It seems that the bottom edge can be made by the high edge, so how do I choose the high edge or the bottom edge?

xutong

@maychang[/url] Please help me if you have time.

maychang

xutong posted on 2023-4-10 18:41 @maychang Teacher, please help me if you have time

Use your terms [high side switch] and [bottom side switch].

The advantage of using a high-side switch is that one end of the load is grounded, while the load of a bottom-side switch cannot be grounded.

Compared with P-channel MOS tubes, N-channel MOS tubes have higher withstand voltage, larger current capacity, and smaller on-resistance, so N-channel MOS tubes should be used as much as possible. However, if N-channel MOS tubes are used as high-side switches, the gate of the MOS tube needs to be driven to a higher potential than the positive end of the power supply, which means that an auxiliary power supply is required as a driving circuit, which is more troublesome. This problem does not exist for bottom-side switches.

qwqwqw2088

Battery powered, such as battery powered in cars, flashlights
Suitable for high-end grounding, the negative pole of the battery is the ground, and the high-end switch is easy to detect fault anomalies

Low-side connection. When other power supplies are used, the negative pole of the power supply is not necessarily equal to the ground, that is, the negative pole of the power supply is different from the ground.

There are also cases where grounding is required on the low side to maintain a reference point for the signal.

qwqwqw2088

Because the ground is not simply divided into positive and negative in a multi-power system, but a common end.

chunyang

The key lies in the significance of the ground loop in the application. For applications that must be grounded, only high-side control can be used. If there is no such requirement, a flexible choice is made based on the characteristics of the control signal, with cost first as the principle.

xutong

maychang posted on 2023-4-11 10:45 Use your terms [high side switch] and [bottom side switch]. The advantage of using a high side switch is that one end of the load is grounded, and the bottom side switch load cannot be connected...

High-side switches generally have charge pumps inside, so driving NMOS is not a problem.

In this way, the MOS of N and P are almost the same.

xutong

qwqwqw2088 posted on 2023-4-11 10:59 Because the ground is not simply divided into positive and negative in a multi-power system, but a common end.

But it makes no difference to the load, since it is 1-to-1 anyway.

xutong

chunyang published on 2023-4-11 16:56 The key lies in the significance of the ground loop in the application. For applications that must be grounded, only high-side control can be used. If there is no such requirement, then according to the control signal...

This explanation is more reasonable

xutong

qwqwqw2088 posted on 2023-4-11 10:59 Because the ground, in a multi-power system, is not simply divided into positive and negative, but a common end.

In fact, the high side and the bottom side share a common port.

In addition, if the fault is abnormal, the bottom edge can also be detected if the load current is abnormal.

xutong

chunyang posted on 2023-4-11 16:56 The key lies in the significance of the ground loop in the application. For applications that must be grounded, only high-side control can be used. If there is no such requirement, then according to the control signal...

I think this explanation is more reasonable. The functions are actually not much different.