AN185 - MPQ5850: 36V, Smart Diode Controller with Reverse Protection, AEC-Q100

Application Note

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Abstract

The MPQ5850 is a 36V, smart diode controller with reverse polarity protection designed for automotive applications.

The device can rectify alternating voltages up to 100kHz. For example, the MPQ5850 can rectify alternating voltages for a faulty automotive alternator or DC switching power supply.

In switching applications (e.g. O-rings), the MPQ5850 prevents negative currents from flowing back through a power supply unit or a battery.

The MPQ5850 can replace a power diode or an unregulated P-channel MOSFET rectifier solution with a regulated N-channel MOSFET. Replacing either of these with the MPQ5850 reduces power loss and temperature.

Introduction

The MPQ5850 drives an external N-channel MOSFET and converts it to an active diode with a 20mV forward voltage drop. AN185 shows examples of this, such as LV124 AC rectification, ISO pulses, and parallel connection of voltage sources (e.g. O-rings).

MPQ5850 Applications

The MPQ5850 applications are listed below:

Automotive System Protections, Reverse Polarity
Automotive Systems, LV124 and ISO Pulses
Automotive Advanced Driver-Assistance Systems (ADAS), Cameras
Automotive Infotainment Systems, Including Digital Clusters and Head Units
Battery-Powered Systems
O-Rings

EVQ5850-J-00A Evaluation Board

The EVQ5850-J-00A is an evaluation board designed to demonstrate the capabilities of the MPQ5850. A large number of circuits can be tested on the evaluation board. The EVB layout also allows EMC filters to be tested at the input and the output.

Evaluation Board Layout

Figure 1 shows the evaluation board with a TVS diode, an optional EMC input filter, and an optional EMC output filter, prepared for different MOSFET packages.

Figure 1: EVQ5850-J-00A (4-Layer PCB)

Basic Automotive Measurements

Figure 2 shows the typical application circuit used for LV124 and ISO pulse measurements. This circuit is suitable for a wide range of applications.

Figure 2: MPQ5850 Automotive Test Application for LV124 and ISO Pulse Measurements ^{(1) (2)}

Notes:
1) C1, C3, D1, and LC_OUT can be different from the values listed in Figure 2. The minimum C1 is 10nF. A larger C1 improves the stability of the source voltage (V_SOURCE). Choose C1 to meet the application’s EMC requirements.
2) The C3 capacitor is optional. C3 rejects EMC transients between V_SOURCE and the drain voltage (V_DRAIN). The MPQ5850 is supplied by V_DRAIN internally. C3 can be below 4.7µF.

LV124 Measurement

LV124 is a quality and reliability test standard jointly established by German automotive manufacturers, applied to in-vehicle electric components for the 12V electrical system.

The LV124 measurements are made using an Ametek 200Q series voltage-drop simulator (VDS 200Q) and a 180cm harness with an impedance (Z). Each power supply line consists of an impedance (Z) that is measured with an impedance LCR meter for inductance (L) and resistance (R). The impedance (Z) can be calculated with Equation (1):

$$Z = L(µH) + R(mΩ)$$

Where L is 1.1µH, R is 17.5mΩ, and the harness length is 180cm.

ISO 7637-2 Pulse Measurement

The ISO 7637-2 standard defines specific test methods and procedures to ensure that a part’s conducted electrical transients are compatible with the passenger cars and commercial vehicles (with 12V or 24V electrical systems) in which the part is installed.

The pulse measurements are made using an Ametek 200N series ultra-compact simulator (UCS 200N), a 200N series load dump generator (LD200N), a 50cm harness with an impedance (Z), and thin lab cables. The impedance (Z) can be calculated with Equation (1). Where L is 0.5µH, R is 15mΩ, and the harness length is 50cm.

Select the optional LC_OUT filter for the desired hold-up time. Select D1 for the required pulse strength.

Optional LC_OUT Not In Use

The C4 capacitor should be ≥220µF; however, it is recommended that C4 be ≥470µF.

Control Modes

The MPQ5850 has two control modes: mode A and mode B. The MOSFET source to drain voltage (V_{SOURCE_DRAIN}) can be calculated with equation (2):

$$V_{SOURCE\_DRAIN} = I_{DRAIN} \times R_{(DS)ON}$$

Where I_DRAIN is the drain current, and R_(DS)ON is the on resistance.

In mode A, V_{SOURCE_DRAIN} is in regulation (20mV), and the MOSFET operates within the analog range. R_(DS)ON is set at a higher value than the minimum R_(DS)ON. The MPQ5850 control loop adjusts R_(DS)ON for a constant 20mV V_{SOURCE_DRAIN}.

In mode B, V_{SOURCE_DRAIN} is not in regulation (>20mV), and the gate to source voltage (V_{GATE_SOURCE}) turns on the MOSFET fully. R_(DS)ON is set to the minimum R_(DS)ON value. The MPQ5850 drives V_{GATE_SOURCE} to its maximum voltage (12V).

The MPQ5850 transitions between mode A and mode B automatically.

If the rated current is low, then the MPQ5850 operates in mode A. If the rated current is high, then the device operates in mode B.

Select the MOSFET according to the desired RDS(ON) and power dissipation. The MPQ5850 can drive most common-sized N-channel MOSFETs. This included both standard and logic-level MOSFETs.

Mode A (V_{SOURCE_DRAIN} Is in Regulation)

Figure 3 shows a measurement in mode A. V_{GATE_SOURCE} is 9.935V, which is below the maximum V_{GATE_SOURCE} (12V). The MOSFET has not reached the minimum R_DS(ON). V_{SOURCE_DRAIN} is measured using a digital multimeter.

Figure 3: Mode A (V_{SOURCE_DRAIN} = 20mV, I_LOAD = 7A)

Mode B(V_{SOUCE_DRAIN} Is Not in Regulation)

Figure 4 shows a measurement in mode B. V_{GATE_SOURCE} is 12.21V, which exceeds the maximum V_{GATE_SOURCE} (12V). The MOSFET has reached the minimum R_DS(ON). V_{SOURCE_DRAIN} is measured using a digital multimeter.