A General Introduction to LM25145 Synchronous Buck DC-DC Controller

LM25145RGYR Pinout

Symbol 

LM25145 Symbol

Footprint

LM25145 Footprint

3D Model

LM25145 3D Model

The LM25145 is a 42-V synchronous buck controller that features all of the functions necessary to implement a high-efficiency step-down power supply with an output voltage ranging from 0.8 V to 40 V. The voltage-mode control architecture uses input feedforward for excellent line transient response over a wide VIN range. Voltage-mode control supports the wide duty cycle range for high input voltage and low dropout applications as well as when a high voltage conversion ratio (for example, 10-to-1) is required. Current sensing for cycle-by-cycle current limit can be implemented with either the low-side FET RDS(on) or a current sense resistor. The operating frequency is programmable from 100 kHz to 1 MHz.

The LM25145 drives external high-side and low-side NMOS power switches with robust 7.5-V gate drivers suitable for standard threshold MOSFETs. Adaptive dead-time control between the high-side and low-side drivers is designed to minimize body diode conduction during switching transitions. An external bias supply can be connected to the VCC pin to improve efficiency in high-voltage applications. A user-selectable diode emulation feature enables discontinuous conduction mode operation for improved efficiency and lower dissipation at light-load conditions.

• Versatile synchronous buck  DC-DC  controller

• Wide input voltage range of 6V to 42V

• Adjustable output voltage From 0.8V to 40V

• Meets EN55022 /  CISPR 22   EMI  standards

• Lossless R_DS(on) or shunt current sensing

• Switching frequency from 100kHz to 1MHz

• SYNC In and SYNC out capability

• 40ns Minimum on-time for high V_IN / V_OUT ratio

• 140ns minimum off-time for low dropout

• 0.8V Reference with ±1% feedback accuracy

• 7.5V Gate drivers for standard V_TH MOSFETs

• 14ns Adaptive dead-time control

• 2.3A Source and 3.5A sink capability

• Low-side soft-start for pre-biased start-up

• Adjustable soft-start or optional voltage tracking

• Fast line and load transient response

• Voltage-mode control with line feedforward

• The high gain-bandwidth error amplifier

• A precision enables input and open-drain power good indicator for sequencing and control

• Inherent protection features for robust design

• Hiccup mode overcurrent protection

• Input  UVLO  with hysteresis

• V_CC and Gate drive  UVLO protection

• Thermal shutdown protection with hysteresis

• VQFN-20 Package with wettable flanks

• Telecom infrastructure

• Factory automation

• Test and measurement

• Industrial motor drives

The LM25145 functional block diagram is shown below:

LM25145RGYR Functional Block Diagram

The following figure shows a typical application circuit and efficient performance of LM25145:

LM25145 Typical Application Circuit and Efficiency Performance, VOUT = 5 V, FSW = 225 kHz

LM25145 Package

A buck or step-down converter is a DC/DC switch mode power supply designed to buck (or lower) an unregulated DC supply's input voltage to a stabilized lower output voltage. Buck converters are highly appreciated for their extraordinarily high efficiency, which can easily surpass 95 per cent when compared to ordinary voltage regulators. The simplified circuit schematic below depicts how current flows across the circuit during a buck converter switching event.

Buck Converter Circuit

A boost converter is a DC/DC switch mode power supply designed to boost (or enhance) an unregulated DC supply's input voltage to a stabilized higher output voltage. A boost converter, like a buck converter, uses an inductor, diode, capacitor, and power switch to adjust the output voltage, but they are organized differently. The simplified circuit schematic below depicts how current travels through the circuit during a boost converter switching event.

Boost Converter Circuit

The output voltage of a boost converter is controlled by the mark-space ratio of the PWM signal to be equal to or greater than V in. Because power is conserved, a boost converter that supplies three times the input voltage can only supply one-third of the current that it pulls from the supply. Boost converters, on the other hand, are highly popular in battery-powered devices, where a pair of batteries may give 3V but must power a 5V circuit.