ОПИСАНИЕ

The LT3510 is a dual current mode PWM step-down DC/DC converter with two internal 2.5A switches. Independent input voltage, feedback, soft-start and power good pins for each channel simplify complex power supply tracking/sequencing requirements.Both converters are synchronized to either a common external clock input or a resistor programmable fi xed250kHz to 1.5MHz internal oscillator. At all frequencies, a180° phase relationship between channels is maintained,reducing voltage ripple and component size. Programmable frequency allows for optimization between efficiency and external component size.Minimum input-to-output voltage ratios are improved by allowing the switch to stay on through multiple clock cycles, only switching off when the boost capacitor needs recharging, resulting in ~95% maximum duty cycle.Each output can be independently disabled using its own soft-start pin, or by using the SHDN pin the entire part can be placed in a low quiescent current shutdown mode.The LT3510 is available in a 20-lead TSSOP package with exposed lead frame for low thermal resistance.

 

ОСОБЕННОСТИ

•Wide Input Range: 3.1V to 25V

•Two Switching Regulators with 2A Output Capability

•Independent Supply to Each Regulator

•Adjustable/Synchronizable Fixed Frequency Operation from 250kHz to 1.5MHz

•Antiphase Switching

•Outputs Can be Paralleled

•Independent, Sequential, Ratiometric or Absolute Tracking Between Outputs

•Independent Soft-Start and Power Good Pins

•Enhanced Short-Circuit Protection

•Low Dropout: 95% Maximum Duty Cycle

•Low Shutdown Current: <10μA

•20-Lead TSSOP Package with Exposed Leadframe

 

ПРИЛОЖЕНИЯ

•DSP Power Supplies

•Disc Drives

•DSL/Cable Modems

•Wall Transformer Regulation

•Distributed Power Regulation

•PCI Cards

 

ИНФОРМАЦИЯ О ПРИЛОЖЕНИЯХ

The LT3510 is dual channel, constant frequency, current mode buck converter with internal 2A switches. Each channel is identical with a common shutdown pin, internal regulator, oscillator, under voltage detect, thermal shutdown and power-on reset.If the SHDN pin is taken below its 1.28V threshold theLT3510 will be placed in a low quiescent current mode.In this mode the LT3510 typically draws 9μA from VIN1and <1μA from VIN2. In shutdown mode the PG is active with a typical sink capability of 50μA for VIN1 voltage greater than 2V.The two regulators are constant frequency, current mode step-down converters. Current mode regulators are controlled by an internal clock and two feedback loops that control the duty cycle of the power switch. In addition to the normal error amplifier, there is a current sense amplifier that monitors switch current on a cycle-by-cycle basis.This technique means that the error amplifier commands current to be delivered to the output rather than voltage.A voltage fed system will have low phase shift up to the resonant frequency of the inductor and output capacitor,then an abrupt 180°, shift will occur. The current fed system will have 90° phase shift at a much lower frequency,but will not have the additional 90° shift until well beyond the LC resonant frequency. This makes it much easier to frequency compensate the feedback loop and also gives much quicker transient response.The Block Diagram in Figure 1 shows only one of the switching regulators whose operation will be discussed below. The additional regulator will operate in a similarmanner with the exception that its clock will be 180° out of phase with the other regulator.When, during power up, the POR signal sets the soft-start latch, both SS pins will be discharged to ground to ensure proper start-up operation. When the SS pin voltage drops below 80mV, the VC pin is driven low disabling switching and the soft-start latch is reset. Once the latch is reset the soft-start capacitor starts to charge with a typical value of 3.25μA.The error amplifier is a transconductance amplifier that compares the FB voltage to the lowest voltage present at either the SS pin or an internal 0.8V reference. Compensation of the loop is easily achieved with a simple capacitor or series resistor/capacitor from the VC pin to ground.