Intelligent power devices for vehicles to reshape the secondary market

The automotive electronics industry has become the driving force for intelligent low-voltage load control. With the use of smart self-protection devices for motor vehicles' standard electrical systems instead of fuses and discrete components, they have been widely used in other markets. Smart power devices used in consumer electronics products are more cost-effective, fault-tolerant, more adaptable, and more reliable. This expanding market has unique requirements for standardized devices, and semiconductor vendors are happy to incorporate these standardized devices into their business plans.

Market Background In today's automotive power distribution and electrical control systems, smart high-side switches are standard building blocks. Mid-high current devices with diagnostic capabilities virtually eliminate the fuses and resettable circuit breakers used in automotive load management.

In distribution systems, individual circuits and associated wiring are protected by intelligent high-side switches. In the vehicle body, lighting and drive system, each load is driven by intelligent devices that may include diagnostics provided by current sensing, fixed parameter diagnostics with status feedback, and/or self-protection features. Autonomous self-protection has become almost universal. The first generation of high-current smart devices have a single-channel output function, and their discrete interfaces use the mainstream package outline. Full implementation of a common vehicle may require dozens of high-side smart switches. Although these switches are still widely used in the selective load of many automotive distribution centers, the number is small. To minimize I/O requirements for automotive systems, new smart power device options include serial bus interfaces, multi-channel outputs, and soft-limit programmability.

However, OEM architecture-specific components may have unknown product life cycles, potential mandatory design changes, or become EOLs that lead to unforeseen redesigns. The higher the degree of integration of the soft functions in the multi-channel device, the higher the design optimization. However, to better serve the secondary market is a standardized device that is provided by multiple sources and has the lowest software complexity.

Secondary manufacturers using standardized smart power devices can be expected to have the highest reliability of these devices because these devices are fully AECQ101 compliant and their cost is still driven by high global sales in multiple markets.

The high-side switch high-side switch is the most common device. They replace the traditional fuses to protect the line, while controlling instead of relays or silicon load switches. There are two common deployments that serve a wide range of load currents with similar functionality to vendors in the market:

(1) High load current—Requires a battery reference interface for the pre-drive transistor, typically with a certain ratio of current feedback. These devices feature reverse voltage protection to protect the MOSFET under reverse load conditions.

Figure 1 Vbb reference interface (FDDS10H04)

Figure 2 Logic Level Interface Block Diagram (FDDS100H06)

(2) Low load current - Ground reference logic level feedback with and without status feedback.

Operating characteristics and charge pump size typically support PWM up to 250Hz illumination. These types of devices are designed to provide clamping for rapid energy decay when driving inductive loads such as solenoid valves.

DC Motor Drive For DC motor loads, P/N half-bridge devices in normal size and package are available from multiple vendors. For variable high-current motor control, the P/N half-bridge provides self-protection, load current monitoring, and higher frequency PWM operation.

These high-side switch and high-current half-bridge diagrams show a number of common self-protection features:

• Short Circuit Protection • Current Limiting • Thermal Shutdown • Overvoltage Protection and Load Dump Compatibility • Undervoltage with hysteresis • ESD protection applications High-side smart switches are the most commonly used devices in lighting. In a 12V system, typical plug-in fuses have a current range of 3A to 30A. With the advent of smart power devices, plus the diagnostic capabilities of a single circuit, the lighting load tends to be a lower current in each circuit, thus enabling more individual circuit diagnostics. Since the marker and position lamps evolved primarily based on LEDs, the load current further decreased.

For the secondary market, this usually results in the controller family having a variable number of standardized outputs that can be programmed or adjusted according to the specific product configuration. In the emergency vehicle lighting market, the specific order of lighting activation may vary from customer to customer. In the small yacht and marine market, in addition to lighting requirements, there may also be a need for auxiliary power supplies or control devices for DC motors of various types of pumps, wipers or fans.

Figure 4 shows a general load controller block diagram that can be scaled for different applications and markets. There are four basic load families defined by universal outputs; three of them are for standard loads, such as lighting or power supply, and the remaining one is for speed-regulated DC motors:

Figure 3 P/N half-bridge diagram Figure 4 Universal load controller • Low current <4A (mainly used for LED and single filament sign lighting)

• Medium current <20A (for lighting, instruments and auxiliary power supplies)

• High current 10A to 30A (for higher power lighting and equipment power supply)

• High-current motor drive <35A (for speed-regulated cooling fans and pumps in unidirectional half-bridge and bi-directional full-bridge operation)

Imagine an application (for example, a small ship) in which a one-way motor on the ship outputs a fan for driving the bilge and a pump for the bilge. Bi-directional motor output can be used for power regulation operation. The remaining power switches can be used for dock lighting, boat lighting, cockpit lighting, pressure gauge power, oil pumps, wipers, whistle, and all other low voltage loads.

Table 1: Fairchild smart power products These same load types and functions are similar for functional devices, RV systems, and garden machines that allow reuse of a large number of design blocks.

Since the leakage current of all smart power devices is designed to be minimal, the Vbat power supply in Figure 4 can be directly connected to the battery system in some applications.

Common Load Types and Design Problems Resistivity—typical loads with dominant resistance can be driven without new components. This allows pulse width modulation (PWM) of incandescent and LED lighting.

Inductive—If an un-suppressed inductor spike (UIS) is within the device's rated range, an inductive load (such as a solenoid valve) can be driven without adding a component.

DC Motors - For non-PWM driven motors, high-side switches can often replace relays. Stress during shutdown may require the use of other components such as a recirculation path or MOV.

Adjustable DC Motors - For adjustable motor control solutions using P/N half-bridges, the PWM frequency, required rise and fall times, and efficiency issues must be considered. The switching frequency affects the accuracy of radiation and PWM. PWM and rise and fall times can affect switching losses (efficiency). Due to the topology of the P/N device, if external battery protection is required, other external components may be required.

Power supply - auxiliary power supply, auxiliary system is usually handled by current load. Excessive inrush current may require a soft start or retry strategy.

Load Line - In any case, the wire gauge must be considered, and that is the autonomous short-circuit protection limit of the smart power device.

One of the most common design issues for smart power load control is the reverse battery voltage. Normally, lighting does not require reverse battery voltage protection.

The reverse battery compatibility and protection of other loads must be carefully checked separately. Reverse-battery structures using P-channel MOSFETs or relays in a Vbat power supply have priority over smart power devices. Power relays that are common to all circuits and require reverse battery protection can also provide "zero off state" power consumption. For long-term unused devices, this issue may require special attention.

Fairchild's products provide a complete solution for low-voltage power distribution and load control on the secondary market. High-side switches include:

The FDDS100H06 monolithic device in the DPak 5-pin package is ideal for incandescent, LED-marked, and low-current solenoid valves up to 10W.

The FDDS10H04 and FDBS09H04, respectively packaged in the DPak 5-pin and D2Pak 7-pin packages, are chip-stacked devices capable of handling higher load currents with proportional load monitoring.

The FN7093 in a D2Pak 7-pin package is designed to handle adjustable PWM drives for up to 35A DC motors. It is improved through competitive products that have a higher operating frequency, and the current source and source current are proportional to the current output.

All Fairchild smart power switches are AECQ101 compliant and operate from -40°C to 150°C. Design support includes product documentation, application notes, and field application engineering.