MX74610SS

Part: MX74610

Type: Ideal Diode Controller

Key Specs:

• Max Continuous Reverse Voltage: 55V
• Operating Ambient Temperature: -40°C to +125°C
• Reverse Polarity Response Time: 2.2 µs (typical)
• Quiescent Current (Iq): 0 µA (typical)
• Gate Drive Pull Down Current (reverse): 160 mA (typical)

Features:

• Maximum reverse voltage of 60V
• No Positive Voltage limitation to Anode Terminal
• Charge Pump Gate Driver for External N-Channel MOSFET
• Lower Power Dissipation than Schottky Diode / PFET Solutions
• Low Reverse Leakage Current
• Fast 2μs Response to Reverse Polarity
• -40°C to +125°C Operating Ambient Temperature
• Can be Used in OR-ing Applications
• No Peak Current Limit

Applications:

• Infotainment Systems
• Power Tools (Industrial)
• Transmission Control Unit (TCU)
• Battery OR-ing Applications
• PV BOX

Package:

• SOT23-6L
• MSOP8

• ♦ Maximum reverse voltage of 60V
• ♦ No Positive Voltage limitation to Anode Terminal
• ♦ Charge Pump Gate Driver for External N-Channel MOSFET
• ♦ Lower Power Dissipation than Schottky Diode / PFET Solutions
• ♦ Low Reverse Leakage Current
• ♦ Fast 2μs Response to Reverse Polarity
• ♦ -40°C to +125°C Operating Ambient Temperature
• ♦ Can be Used in OR-ing Applications
• ♦ No Peak Current Limit

♦ 6-Pin SOT23-6L and 8-pin MSOP8

• ♦ Infotainment Systems
• ♦ Power Tools (Industrial)
• ♦ Transmission Control Unit (TCU)
• ♦ Battery OR-ing Applications
• ♦ PV BOX

(VAnode - Cathode = 0.55V, T^A = 25°C, unless otherwise noted)

Characteristic plots

Voltage Across Body Diode vs Vcap Charging Current

Detailed description

Most systems in industrial applications require fast response reverse polarity protection at the input stage. Schottky diodes or P-Channel MOSFETs are typically used in most power systems to protect the load in the case of negative polarity. The main disadvantage of using diodes is voltage drop during forward conduction, which reduces the available voltage and increases the associated power losses. PFET solutions are inefficient for handling high load current at low input voltage.

The MX74610 is a zero Iq controller that is combined with an external N-channel MOSFET to replace a diode or PFET reverse polarity solution in power systems. The voltage across the MOSFET source and drain is constantly monitored by the MX74610 ANODE and CATHODE pins. An internal charge pump is used to provide the GATE drive for the external MOSFET. This stored energy is used to drive the gate of MOSFET. The voltage drop depends on the RDSON of a particular MOSFET in use, which is significantly smaller than a PFET. The MX74610 has no ground reference which makes it identical to a diode.

Feature Description

During T⁰

When power is initially applied, the load current I^D will flow through the body diode of the MOSFET and produce a voltage drop V^f during T⁰ in the following figure. This forward voltage drop V^f across the body diode of the MOSFET is used to charge up the charge pump capacitor Vcap. During this time, the charge pump capacitor Vcap is charged to a higher threshold of 6.3V (typical).

During T¹

Once the voltage on the capacitor reaches the higher voltage level of 6.3V (typical), the charge pump is disabled and the MOSFET turns ON. The energy stored in the capacitor is used to provide the gate drive for the MOSFET (T¹ in the following figure). When the MOSFET is ON, it provides a low resistive path for the drain current to flow and minimizes the power dissipation associated with forward conduction. The power losses during the MOSFET ON state depend primarily on the RDSON of the selected MOSFET and load current. At the time when the capacitor voltage reaches its lower threshold VCAPL 5.15V (typical), the MOSFET gate turns OFF. The drain current I^D will then begin to flow through the body diode of the MOSFET, causing the MOSFET body diode voltage drop to appear across Anode and Cathode pins. The charge pump circuitry is re-activated and begins charging the charge pump capacitor. The MX74610 operation keeps the MOSFET ON at approximately 98% duty cycle (typical) regardless of the external charge pump capacitor value. This is the key factor to minimizing the power losses. The forward voltage drop during this time is determined by the RDSON of the MOSFET.

Output Voltage and Vgate Operation at 1A Output Current Pin Operation

Anode and Cathode Pins

The MX74610 Anode and Cathode pins are connected to the source and drain of the external MOSFET. The current into the Anode pin is 30μA (typical). When power is initially applied, the load current flows through the body diode of the external MOSFET, the voltage across Anode and Cathode pins is equal to the forward diode drop Vf. The minimum value of V^f required to enable the charge pump circuitry is 0.48V. Once the MOSFET is turned ON, the Anode and Cathode pins constantly sense the voltage difference across the MOSFET to determine the magnitude and polarity of the voltage across it. When the MOSFET is on, the voltage difference across Anode and Cathode pins depends on the RDSON and load current. If voltage difference across source and drain of the external MOSFET becomes negative, this is sensed as a fault condition by Anode and Cathode pins and gate is turned off by Gate Pull Down pin as shown in the following figure. The reverse voltage threshold across Anode and Cathode to detect the fault condition is -20mV. The consistent sensing of voltage polarity across the MOSFET enables the MX74610 to provide a fast response to the power source failure and limit the amount and duration of the reverse current flow.

MX74610

Reverse Polarity Protection Smart Diode Controller

Gate Shut Down Timing in the Event of Reverse Polarity VCAPH and VCAPL Pins

VCAPH and VCAPL are high and low voltage thresholds respectively that the MX74610 uses to detect when to turn the charge pump circuitry ON and OFF. The capacitor charging and discharging time can be correlated to the duty cycle of the MOSFET gate. The following figure shows the voltage behavior across the Vcap. During the period T0, the capacitor is storing energy from the charge pump. The MOSFET is turned off and current flow is only through the body diode during this period. The conduction through body diode of the MOSFET is for a very small period (2% typical) which rules out the chances of overheating the MOSFET, regardless of the output current. Once the capacitor voltage reaches its high threshold, the MOSFET is turned ON and charge pump circuity is deactivated until the Vcap reaches its lower voltage threshold again T1. The voltage difference between Vcap high and low threshold is typically 1.15V. The MX74610 charge pump has 46μA charging capability with 5-8MHz frequency.

Vcap Charging and Discarding by the Charge Pump The Vcap current consumption is 1μA (typical) to drive the gate. The MOSFET OFF time (T0) and ON time (T1) can be calculated using the following expression.

ΔT = C×dV / dT

Where:

• C = Vcap Capacitance
• dV = 1.15V
• dI = 46μA for charging
• dI = 0.95μA for discharging

Note: Temperature dependence of these parameters – The duty cycle is dependent on temperature since the capacitance variation over temperature has a direct correlation to the MOSFET OFF and ON periods and the frequency. If the capacitor varies 20% the periods and the frequency will also vary by 20% so it is recommended to use a quality X7R/COG cap and not to place the cap near high temperature devices. The variation of the capacitor does not have a thermal impact in the application as the duty cycle does not change.

Gate Drive Pin

When the charge pump capacitor is charged to the high voltage level of 6.3V (typical), the Gate Drive pin provides a 6.8μA (typical) of drive current. When the charge pump capacitor reaches its lower voltage threshold of 5.15V (typical), Gate is pulled down to the Anode voltage VIN. During normal operation, the gate turns ON and OFF with a slow 2ms slew rate to avoid switching noise and EMI issues. To protect the gate of the MOSFET, a built-in internal 11.5V Zener clamp the maximum gate to source voltage VGS(MAX).

Gate Pull Down Pin

The Gate Pull Down pin is connected to the Gate Drive pin in a typical application circuit. When the controller detects negative polarity, possibly due to failure of the input supply or voltage ripple, the Pull-Down quickly discharges the MOSFET gate through a discharge transistor. The Gate Pull Down pin can discharge the MOSFET gate capacitance with 160mA pull down current to speed up the MOSFET turn OFF time. This fast pull down reacts regardless of the Vcap charge level. If the input supply abruptly fails, as would happen if the supply gets shorted to ground, a reverse current will temporarily flow through the MOSFET. This reverse current can be due to parallel connected supplies and load capacitance and is dependent upon the RDSON of the MOSFET.

When the negative voltage across the Anode and Cathode pins reaches -20mV (typical), the MX74610 immediately reacts and discharges the MOSFET gate capacitance. A MOSFET with 5nF of effective gate capacitance can be turned off by the MX74610 within 2μs (typical). The fast turnoff time minimizes the reverse current flow from MOSFET drain by opening the circuit. The reverse leakage current does not exceed 110μA for a constant 13.5V reverse

MX74610

Reverse Polarity Protection Smart Diode Controller

voltage across Anode and Cathode pins. The reverse leakage current for a Schottky diode is 15mA under the same voltage and temperature conditions.

Device Functional Modes

Body Diode Conduction Mode

The MX74610 solution works like a conventional diode during this time with higher forward voltage drop. The power dissipation during this time can be given as:

PDissipation = (VForward Drop)×(IDrain Current)

However, the current only flows through the body diode while the MOSFET gate is being charged to VGS(TH). This conduction is only for 2% duty cycle; therefore, it does not cause any thermal issues.

Body Diode ON Time = C×(VCAPH - VCAPL) / ICharge Current The MOSFET Conduction Mode

The MOSFET is turned on during this time and current flow is only through the MOSFET. The forward voltage drops, and power losses are limited by the RDSON of the specific MOSFET used in the solution. The MX74610 solution output is comprised of the MOSFET conduction mode for 98% of its duty cycle. This period is given by the following expression:

MOSFET ON Time = C × (VCAPH - VCAPL) / IDischarge Current Duty Cycle Calculation

The MX74610 has an operating duty cycle of 98% at 25°C and >90% at 125 ̊C. The duty cycle doesn't depend on the Vcap capacitance value. However, the variation in capacitance value over temperature has direct correlation to the switching frequency between the MOSFET and body diode. If the capacitance value decreases, the charging and discharging time will also decrease, causing more frequent switching between body diode and the MOSFET condition. The following expression can be used to calculate the duty cycle of the MX74610:

Duty Cycle (%) = (MOSFET ON Time) ×100 / (MOSFET ON Time + Body Diode ON Time)

Application and Implementation

Application Information

The MX74610 is used with N-Channel MOSFET controller in a typical reverse polarity protection application. The schematic for the typical application is shown in the following figure where the MX74610 is used in series with a battery to drive the MOSFET Q1. The TVS+ and TVS- are not required for the MX74610. However, they are typically used to clamp the positive and negative voltage surges respectively. The output capacitor Cout is recommended to protect the immediate output voltage collapse because of line disturbance.

Typical Application Schematic

Capacitor Selection

A ceramic capacitor should be placed between VCAPL and VCAPH. The capacitor acts as a holding tank to power up the control circuitry when the MOSFET is on.

When the MOSFET is off, this capacitor is charged up to higher voltage threshold of ~6.3V. Once this voltage is reached, the Gate Drive of MX74610 will provide drive for the external MOSFET. When the MOSFET is ON, the voltage across its body diode is collapsed because the forward conduction is through the MOSFET. During this time, the capacitor acts as a supply for the Gate Drive to keep the MOSFET ON.

The capacitor voltage will gradually decay when the MOSFET is ON. Once the capacitor voltage reaches a lower voltage threshold of 5.15V, the MOSFET is turned off and the capacitor gets recharged again for the next cycle.

A capacitor value of 220nF to 4.7uF with X7R/COG characteristic and 16V rating or higher is recommended for this application. A higher value capacitor sets longer MOSFET ON time and OFF time, however, the duty cycle remains at ~98% for MOSFET ON time irrespective of capacitor value.

If the Vcap value is 2.2μF, the MOSFET ON time and OFF time can be calculated using the following equation:

MOSFET ON Time = (2.2μF × 1.15V)/0.95μA = 2.66s

Body Diode ON Time = (2.2μF × 1.15V)/46μA = 55ms

The duty cycle can be calculated using the following

equation:

Stresses beyond those listed in Absolute Maximum Ratings may cause permanent damage to the device. Exposure to absolute maximum rating conditions for extended periods may affect reliability. Functional operation of the device at any conditions beyond those indicated in the Recommended Operating Conditions section is not implied.