High-frequency load point power supply is difficult, why? This high-current intelligent power driver solves the problem

At present, new energy vehicles are in a stage of rapid development, which poses new challenges to the stable operation of power load power supply systems. Is there a new type of high-current load point converter that can meet the growing demand for high efficiency, high density, and reliable power levels in power load system design? In response to this, ADI has launched the LTC7050 SilentMOS™ series of intelligent power drivers, which has become a powerful tool to effectively solve the above problems.

Why ADI LTC7050 SilentMOS series is the first choice

The LTC7050 can be configured to power two independent power rails, each with separate on/off control, fault reporting and current sense outputs; or, the device can be configured as a dual-phase single output converter. The LTC7051 single channel 140A power stage leverages the LTC7050 core design to provide higher power density with a single inductor.

The LTC7050 dual-channel monolithic power driver fully integrates high-speed drivers and low-resistance half-bridge power switches, along with comprehensive monitoring and protection circuitry, in an electrically and thermally optimized package. With the right high-frequency controller, the power driver forms a compact, high-current regulator system with advanced efficiency and transient response. The Silent Switcher® 2 architecture and integrated bootstrap supply enable high-speed switching, reduce high-frequency power losses by attenuating input supply or switch node voltage overshoots, and minimize the accompanying EMI.

Low switch node stress enhances power stage robustness

In conventional buck regulator designs, the hot loop inductance between the input capacitor and the power MOSFET causes large spikes at the switch node. SilentMOS LTC7050 uses Silent Switcher 2 technology to integrate the critical VIN decoupling capacitor inside the LQFN package. The reduction of the hot loop leads to reduced parasitic inductance. In addition, the fully symmetrical layout eliminates electromagnetic fields. Figure 1 compares the LTC7050 layout with a conventional power driver. As shown in Figure 2, when the input voltage is 12V and the output is fully loaded, the peak voltage at the switch node is only 13V. There is ample margin between the peak voltage stress on the power MOSFET and its rated voltage, ensuring the reliability of the device. The fully integrated hot loop eliminates PCB layout sensitivity and makes complex electromagnetic cancellation design clearly visible to the user. To properly measure the switch node ringing, use a coaxial cable and solder it from the switch pin to the local ground, then measure the waveform on an oscilloscope with matched impedance.

Figure 1. The SilentMOS LTC7050 has a small, symmetrical internal thermal loop to minimize ringing. (a) shows the LTC7050 and (b) shows a conventional DrMOS module.

High efficiency and advanced packaging enable high power density

The LTC7050 has low conversion losses, making it more efficient than conventional DrMOS modules in high-frequency designs. The overlap time of the power device current and voltage is determined by the drive speed. In multi-chip DrMOS modules, the drive speed is limited by the inductance between the driver and the power MOSFET and between the driver and its capacitors. Driving the MOSFET gate too fast can cause overvoltage on the gate of the power device/driver and cause failure. In addition, high di/dt causes large spikes at the switch node because the thermal loop inductance cannot be ignored.

The LTC7050's driver is integrated on the same die as the power loop, and all gate driver capacitors are in the package. Since the bonding wires are eliminated, the parasitic inductance in each drive loop is close to zero. Compared with multi-chip DrMOS modules, the LTC7050 turns on and off power devices much faster. The typical rising edge of the switch node voltage is as short as 1ns, as shown in Figure 2. The best-in-class drive speed greatly reduces conversion losses. The high drive speed allows the LTC7050 to have zero dead time, which greatly reduces diode conduction and reverse recovery losses.

Figure 2. Switching node waveform; ILOAD = 25A/phase

Careful design improves power conversion efficiency at high switching frequencies. Figure 3 shows the 12V to 1.8V conversion efficiency and loss curves at 600kHz and 1MHz. For the 1MHz design, the peak efficiency exceeds 94%.

Figure 3. Efficiency and loss curves

Figure 4 shows the 12V to 1.0V conversion efficiency and loss curves at 600kHz and 1MHz.

Figure 4. Efficiency and loss curves

For the 1MHz design shown in Figure 4, the efficiency is almost 90% at 60A, while the total power loss (including inductor losses) is less than 7W. The thermal impedance of the LTC7050’s thermally enhanced 5mm × 8mm LQFN package is low at 10.8°C/W. The low losses and low thermal impedance allow the LTC7050 to replace two industry standard 5mm × 6mm DrMOS modules . Figure 5 shows the thermal image of the LTC7050 at 12V to 1V/60A conversion with a switching frequency of 1MHz. The case temperature rise is approximately 68°C over the entire temperature range.

Figure 5. Thermal image of the LTC7050

Test conditions: VIN = 12V, VOUT = 1V, IOUT = 60A, no airflow, board running continuously for more than 30 minutes.

Strict fault alarm and protection system ensures load safety

The LTC7050 series integrates a range of fault detection, alarm and protection features to ensure system safety.

The LTC7050 provides fully tested overcurrent protection for both the top and bottom FETs. When the power device extracts the instantaneous current flowing through the power FET, the devices on the same die should be matched. The monolithic architecture ensures that the effects of temperature and process variations are fully offset, and the parasitic effects that cause delays in the current sense signal are negligible. These inherent advantages of the monolithic architecture support real-time, accurate current monitoring and protection. Once the overcurrent comparator trips, the affected power device is latched off regardless of the PWM input, the FLTB pin is pulled low to report the fault to the controller, and the reverse device is turned on to continue the inductor current to zero. After the current ramps down to zero, the driver accepts only the PWM signal again. This protection scheme prevents the power stage from continuously jittering around the positive or negative current limit value, avoiding thermal stress on the device. Figure 6 shows the load current ramping up until the positive overcurrent protection is triggered.

Figure 6. LTC7050 overcurrent protection

To ensure that the power devices always operate in the safe operating area, the input overvoltage lockout feature of the LTC7050 forces both power switches to stop switching when the input voltage exceeds the OV threshold. If the power MOSFET is carrying a large current and OV is detected, the reverse power device will continue to flow as described above.

The LTC7050 family provides two temperature measurement interfaces for controllers (such as the LTC3884) or system monitors. The TDIODE pin is connected to a PN junction diode to measure the IC junction temperature using the VBE method or the ΔVBE method. TMON is a dedicated pin that reports the die temperature with an industry standard 8mV/°C slope. Unlike standard DrMOS modules that combine analog temperature monitoring with other fault alerts on a single pin, the LTC7050’s TMON is only pulled to VCC when the die temperature is at least 150°C. In other fault conditions, TMON will continue to report the die temperature when the FLTB open-drain output is pulled low. The monolithic architecture enables TDIODE and TMON to reflect the temperature of the power devices well. When multiple power stages are used in a multi-phase system, the TMON pins can be tied together to report the highest temperature.

Integrating the bootstrap diode and bootstrap capacitor into the package eliminates the need for a boost pin and the possibility of an accidental short circuit of the bootstrap driver. The voltage of the bootstrap driver is constantly monitored internally. If the voltage falls below the undervoltage threshold, the top FET is turned off to avoid excessive conduction losses.

in conclusion

The LTC7050 SilentMOS monolithic high current intelligent power driver is an excellent solution for high frequency point-of-load applications. The integrated hot loop with symmetrical layout brings many benefits. Fewer external components, smaller PCB size and lower bill of materials cost. Low switch node ringing enhances device reliability. Switching-related losses are low, so it can achieve high efficiency at high switching frequencies and allow the use of small inductors; the size of the output capacitor can also be smaller because the closed-loop bandwidth is higher. Comprehensive monitoring and protection features protect expensive loads under various fault conditions.