Welcome to the training module on the LM3150 Synchronous Simple Switcher Controller.
In this module, we will discuss the feature, application and performance characteristics of the LM315X device. We will also go over block diagrams, examples of schematics and the eval board.
The LM3150 SIMPLE SWITCHER® Controller is an easy to use and simplified step down power controller, capable of providing up to 12A of output current in a typical application. Operating with an input voltage range of 6V-42V, the LM3150 features an adjustable output voltage down to 0.6V. The switching frequency is adjustable up to 1 MHz and the synchronous architecture provides for highly efficient designs. The LM3150 controller employs a Constant On-Time (COT) architecture with a proprietary Emulated Ripple Mode (ERM) control that allows for the use of low ESR output capacitors, which reduces overall solution size and output voltage ripple. The Constant On-Time (COT) regulation architecture allows for fast transient response and requires no loop compensation, which reduces external component count and reduces design complexity.
This device can go into various application areas like Telecom, Networking equipment, routers, security surveillance and power modules.
This chart lists the key performance specification of the LM3051 device. The device can deliver a maximum current output of 12A, a max input voltage of 42 volts, a max operating frequency of 1MHz and with a 95% of Efficiency.
The LM3150 synchronous step-down SIMPLE SWITCHER Controller utilizes a Constant On-Time (COT) architecture which is a derivative of the hysteretic control scheme. COT relies on a fixed switch on-time to regulate the output. The on-time of the high-side switch can be set manually by adjusting the size of an external resistor (RON). To maintain a relatively constant switching frequency as VIN varies, the LM3150 automatically adjusts the on-time inversely with the input voltage. Assuming an ideal system and VIN is much greater than 1V. Control is based on a comparator and the on-timer, with the output voltage feedback (FB) compared with an internal reference of 0.6V. If the FB level is below the reference, the high side switch is turned on for a fixed time, tON, which is determined by the input voltage and the resistor RON. Following this on-time, the switch remains off for a minimum off-time, tOFF, as specified in the Electrical Characteristics table or until the FB pin voltage is below the reference, then the switch turns on again for another on-time period. The switching will continue in this fashion to maintain regulation. During continuous conduction mode (CCM), the switching frequency ideally depends on duty-cycle and on-time only.
When the output voltage is below the comparator's low-voltage threshold, the power stage turns on; the duration of this on-time pulse is a function of how long the output voltage stays below the threshold. As a result, the pulse frequency is not constant, but depends on how the output voltage changes during both the on-time and off-time. Hysteretic control does not require an internal oscillator. Switching frequency depends on the external components and operating conditions such as load current and line voltage, since these parameters influence when the output voltage crosses the hysteretic comparator thresholds.
Constant on-time (COT) control minimizes the change in switching frequency with line variations, which, depending on the particular hysteretic design, would otherwise vary the switching frequency significantly and create many problems. Constant on-time control sets a fixed on-time, which is influenced by input voltage. The on-time becomes inversely proportional to the input voltage. With this feed-forward correction of line variations, the switching frequency will not have to change and as such, the simple relationship of duty cycle to input and output voltage (i.e., D = Vout/Vin), is retained.
This slide shows you the Typical MOSFET, Gate Charge Curve which is obtained by considering the proper component values for R sub limit and Rds(on). The gate drive current from VCC must not exceed the minimum current limit of VCC.
The design guide provides the equations required to design with the LM3150 SIMPLE SWITCHER® Controller. The WEBENCH® design tool can be used with, or in place of this section. We have given the steps for how to design with LM3150 device: The available frequency range for a given input voltage range, is determined by the duty-cycle or Vout/Vin and the minimum On-time and OFF-time.
This is a typical performance characteristics of the device family. The first graphs shows the Efficiency vs load curve at 250 KHz and the 2 nd shows it at 500kHz.
The LM3150 evaluation boards are designed to provide the design engineer with a fully functional power converter, based on Constant On-Time and with Emulated Ripple mode control to evaluate the LM3150 and the entire LM315x family of parts. The evaluation board is pre-configured to use the LM3150 with the output voltage pre-set to 3.3V, and a typical max load current of 10A. There are three different boards that are configured for 250 kHz, 500 kHz, and 750 kHz respectively. The evaluation board allows for a variety of configurations, and this multifunctional capability is used to also accept the fixed output versions of the LM3150 such as the LM3151-3.3, LM3152-3.3, and the LM3153-3.3.
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LM315x Synchronous Simple Switcher® Controller Series
An overview study on Synchronous Simple Switcher® Controller Series
Features, Application and Performance
Simplified block diagram
Design Example schematic and its parameter
LM3150 Evaluation Board details
Features ■ PowerWise® step-down controller ■ 6V to 42V Wide input voltage range ■ Adjustable output voltage down to 0.6V ■ Programmable switching frequency up to 1 MHz ■ No loop compensation required ■ Fully WEBENCH® enabled ■ Low external component count ■ Constant On-Time control ■ Ultra-fast transient response ■ Stable with low ESR capacitors ■ Output voltage pre-bias startup ■ Valley current limit ■ Programmable soft-start
The necessary building blocks for Hysteretic are a reference hysteretic comparator, and a power stage that creates a pulse width modulation (PWM) duty-cycle based on the output of the comparator.
This technique is fast, simple, and low-cost.
When the output voltage is below the comparator's low-voltage threshold, the power stage turns on; the duration of this on-time pulse is a function of how long the output voltage stays below the threshold.
Its disadvantage is its varying switching frequency and ripple voltage requirement at the input (feedback pin) of the comparator.
Pure hysteretic mode control Output ripple across ceramic versus electrolytic capacitors
Constant on-time (COT) control minimizes the change in switching frequency with line variations.
Constant on-time control sets a fixed on-time, which is influenced by only the input voltage.
The on-time becomes inversely proportional to the input voltage. With this feed-forward correction of line variations, the switching frequency will not have to change and so the simple relationship of duty cycle to input and output voltage (i.e., D = Vout/Vin), is retained.
In constant on-time systems, line changes are taken into consideration before they even influence the output voltage.