BD2041AFJ and BD2051AFJ are single-channel high-side switching ICs with overcurrent protection for Universal Serial Bus (USB power lines. These ICs feature low on-resistance N-channel power MOSFETs with low supply current, built-in overcurrent protection circuitry, thermal shutdown circuit breaker, lower voltage lockout and soft-start circuit.

Typical Application Circuit Diagram

feature

Built-in low on-resistance Nch MOSFET (typ = 80mΩ) control input logic

Low activity: BD2041AFJ

Active-High: BD2051AFJ

Soft start circuit

Overcurrent Protection

Thermal shutdown

Undervoltage lockout function

Open-drain error flag output

Reverse current protection at shutdown

Flag output delay

block diagram

Main Specifications

Input Voltage Range: 2.7V to 5.5V

On-resistance: 80mΩ (typ.)

Continuous current load: 0.5A

Overcurrent Threshold: 0.7A (minimum), 1.6A (maximum)

Standby current: 0.01μA (typ.)

Output rise time: 1.2ms (typ)

Operating temperature range: -40°C to +85°C

Configuration diagram

Measurement circuit

Working current

EN, /EN input voltage, output rise/fall time

On-resistance, overcurrent detection

OC output low voltage

Timing diagram

Timing Diagram (BD2041AFJ)

Timing Diagram (BD2051AFJ)

Typical Application Circuit

Application Information

Ringing occurs through the inductance of the power supply line and the IC when excessive current flows due to short-circuiting of the output, etc. This may adversely affect IC operation. To avoid this, connect the IN terminal and GND terminal of the bypass capacitor IC. A value of 1µF or higher is recommended. Pull-up/OC output resistance is 10kΩ to 100kΩ. The set value of CL satisfies the application. This application circuit is not guaranteed to operate. When changing external circuit constants when using the circuit, it is better to have sufficient margin for external components, such as static and transient characteristics and dispersion of IC.

Function Description

1. Switch operation

The IN terminal and the OUT terminal are connected to the drain and source of the switching MOSFET, respectively. The IN terminal is also used as the power input for the internal control circuit. When the EN (/EN) control input turns on the switch, both the IN and OUT terminals are connected to an 80mΩ bidirectional switch. Therefore, the current flows from the OUT terminal to the IN terminal as the current flows from the high level to the lower potential. On the other hand, when the switch is turned off, the reverse flow of current from OUT to IN is prevented because there is no parasitic diode between the drain and source of the switching MOSFET.

2. Thermal Shutdown Circuit (TSD)

If the overcurrent continues, the temperature of the IC will increase sharply. If the junction temperature becomes higher than 140°C (typ) with overcurrent detection, the thermal shutdown circuit operates and turns the power supply off, causing the IC to output an error flag (/OC). Then, when the junction temperature drops below 120°C (Typ), the power switch is turned on and the error flag (/OC) is removed. Unless there is a reason, repeat this operation to eliminate the rise in chip temperature or turn off the output of the power switch. The thermal shutdown circuit operates when the switch is on (EN (/EN) signal is active).

3. Over Current Detection (OCD)

When current flows in each switch, the overcurrent detection circuit limits the current (ISC) and outputs an error flag (/OC)

MOSFET exceeds specification. When the switch is on (EN (/EN) signal is ), the overcurrent detection circuit works active). There are three types of responses to overcurrent:

(1) When the output is in the short circuit state, when the switch is opened, the switch enters the current limit state immediately.

(2) When an output short circuit or a large current load is connected when the switch is turned on, the overcurrent limiting circuit reacts with a very large current flowing. When it exceeds the detection value, current limit is performed.

(3) When the output current is gradually increased, the current limit circuit will not operate over the overcurrent detection value unless the output current is increased. However, when the output current gradually increases and exceeds the detection value, current limiting is performed.

4. Under Voltage Lockout (UVLO)

The UVLO circuit prevents the switch from turning on until VIN exceeds 2.3V (typ). If VIN falls below 2.2V (typ), the switch turns on, then UVLO turns off the power switch. UVLO has 100mV (typ) hysteresis. The undervoltage lockout circuit operates when the switch is open (EN (/EN) signal is active).

5. Error flag (/OC) output

The error flag output is an N-MOS open-drain output. The output is low during overcurrent detection and/or thermal shutdown. Overcurrent detection has a delay filter. This delay filter prevents sending current sense flag transient events during this time, such as inrush current during power-on or hot-plug. If the fault flag output is not used, the /OC pin should be connected to an open circuit or ground.

Over Current Detection, Thermal Shutdown Timing Diagram (BD2041AFJ)

Over Current Detection, Thermal Shutdown Timing Diagram (BD2051AFJ)

Instructions

1. Reverse connection of power supply

Connecting the power supply with reversed polarity will damage the IC. Connect the power supply taking precautions to prevent reverse polarity, such as installing an external diode supply pin between the power supply and the IC power supply.

2. Power cord

Design the PCB layout pattern to provide low impedance power lines. Separate ground and supply lines for digital and analog blocks to prevent ground noise and power lines from digital blocks from affecting analog blocks. Also, connect capacitors to ground on all power pins. When using electrolytic capacitors considering the influence of temperature and temperature, the capacitance value will deteriorate.

3. Ground voltage

Even under transient conditions, make sure that at no time is the voltage on the pin lower than the voltage on the ground pin.

4. Ground wire mode

When using small signal and high current ground traces, the two ground traces should be routed separately, but connected to a single ground at the reference point of the application board to avoid ground caused by fluctuations in small signals and high currents. Also make sure that the ground traces of external components do not cause variations in the ground voltage. The ground wire must be as short and thick as possible to reduce line impedance.

5. Heat dissipation considerations

If the power rating is exceeded, it may cause the chip temperature to rise and chip performance to deteriorate. The absolute maximum ratings for Pd specified in this specification are when the IC is mounted on a 70mm x 70mm x 1.6mm glass epoxy board. If this absolute maximum rating is exceeded, increase the board size and copper area to prevent exceeding the Pd rating.

6. Recommended operating conditions

These conditions represent the range within which the expected characteristics of the IC can be obtained. Electrical characteristics are guaranteed under the conditions of each parameter.

7. Inrush current

When power is first applied to the IC, the internal logic may be unstable and inrush current may flow instantaneously due to internal power supply sequencing and delays, especially if the IC has multiple power supplies. Therefore, special consideration should be given to power coupling capacitors, power traces, ground trace widths, and connection routing.

8. Operation under strong electromagnetic field

Operating the IC in the presence of strong electromagnetic fields may cause the IC to malfunction.

9. Test on the application board

When testing the IC on an application board, you can stress the IC by connecting capacitors directly to the low impedance output pins. Always fully discharge capacitors after each process or step. Power to the IC should always be completely turned off before being connected during inspection or removed from the test setup. To prevent damage from electrostatic discharge, ground the IC during assembly and take similar precautions for shipping and storage during use.

10. Short circuit between pins and installation errors

When mounting the IC on the PCB, make sure the orientation and position are correct. Incorrect installation may damage the IC. Avoid shorting nearby pins to each other, especially ground, power, and output pins. Pin shorts can be caused by a number of reasons, such as metal particles, water droplets (in very humid environments) during assembly, unintentional solder bridge deposits between the pins, to name a few.

11. Unused input pins

The input pins of the IC are usually connected to the gates of the MOS transistors. The gate has very high impedance and very low capacitance. If left unconnected, it can be easily charged by an electric field from the outside. The charge obtained in this way is small enough to have a significant effect on the conduction of the pass transistor resulting in unexpected operation of the IC. Therefore, unused input pins should be connected to power or ground unless otherwise specified.

12. About the input pins of the IC

The monolithic IC contains P+ isolation and a P substrate layer between adjacent components to keep them isolated. A PN junction is formed at the intersection of the P layer with other elements in the N layer, forming a parasitic diode or transistor. For example (see image below): When GND > Pin A and GND > Pin B, the PN junction acts as a parasitic diode. When GND > pin B, the PN junction acts as a parasitic transistor. Parasitic diodes inevitably appear in the structure of ICs. The operation of parasitic diodes can lead to interference between interacting circuits, operational failure or physical damage. Therefore, conditions that cause these diodes to operate, such as applying voltages below the GND voltage to the input pins (and thus to the P-substrate) should be avoided.

Monolithic IC Structure Example

13. Ceramic capacitors

When using ceramic capacitors, consider the change in capacitance, determine the dielectric constant temperature and the reduction in nominal capacitance due to DC bias, etc.

14. Thermal Shutdown Circuit (TSD)

The IC has a built-in thermal shutdown circuit to prevent thermal damage to the IC. Should always operate normally within the power consumption of the IC. However, if the rating is exceeded for a continuous period of time, the junction temperature (Tj) will rise, which will activate the TSD circuit that will shut down all output pins. When Tj falls below the TSD threshold, the circuit automatically resumes normal operation. Note that TSD circuits operate above the Absolute Maximum Ratings, so TSD circuits should be used without thermal damage if they are used in a collective design or for any purpose other than protecting ICs.

15. Thermal Design

Perform thermal design with sufficient margins by considering power dissipation (Pd) for actual usage conditions.