Datasheet LTM4632 (Analog Devices) - 9

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OPERATION
The LTM4632 is a dual output standalone non-isolated With current mode control and internal feedback loop switch mode DC/DC power supply for DDR-QDR4 SRAM compensation, the LTM4632 module has sufficient sta- memory supplies and bus termination. It can deliver two bility margins and good transient performance with a wide output rails which could both sink and source 3A DC cur- range of output capacitors, even with all ceramic output rent with few external input and output ceramic capaci- capacitors. tors, plus a 10mA buffered VTTR (VREF) reference voltage Current mode control provides cycle-by-cycle fast cur- which equal to one half of VDDQIN voltage. rent limiting. An internal overvoltage and undervoltage Two or more module outputs can be easily paralleled to comparators pull the open-drain PGOOD output low if achieve a single VTT output with a higher sink and source the output feedback voltage exits a ±8% window around current capability. Up to 8 phases can be paralleled to run the regulation point. Furthermore, an input overvoltage simultaneously with a good current sharing guaranteed protection been utilized by shutting down both power by current mode control loop. MOSFETs when VIN rises above 17.5V to protect internal This module provides precisely regulated output voltage devices. (VOUT1) programmable via one external resistor from 0.6V Pulling the RUN pin below 1V forces the controller into to 2.5V over 3.6V to 15V input voltage range. With INTVCC its shutdown state, turning off both power MOSFETs and tied to VIN, this module is able to operate from 3.3V input. most of the internal control circuitry. At light load cur- The LTM4632 has an integrated a dual constant on-time rents, burst mode operation can be enabled to achieve valley current mode regulator, power MOSFETs, induc- higher efficiency compared to continuous mode (CCM) by tor, and other supporting discrete components. The typi- setting MODE pin to INTVCC. The TRACK/SS pin is used cal switching frequency is internally set to 1MHz. For for power supply tracking and soft-start programming. switching noise-sensitive applications, the µModule can See the Applications Information section. be externally synchronized to a clock within ±30% of the set frequency. See the Applications Information section.
APPLICATIONS INFORMATION
The typical LTM4632 application circuit is shown in where tOFF(MIN) is the minimum off-time, 45ns typical for Figure 19. External component selection is primarily deter- LTM4632, and fSW is the switching frequency. Conversely mined by the input voltage, the output voltage and the the minimum on-time limit imposes a minimum duty maximum load current. Refer to Table 5 for specific exter- cycle of the converter which can be calculated as nal capacitor requirements for a particular application. DMIN = tON(MIN) • fSW
VIN to VOUT Step-Down Ratios
where tON(MIN) is the minimum on-time, 20ns typical for There are restrictions in the maximum V LTM4632. In the rare cases where the minimum duty IN and VOUT step down ratio that can be achieved for a given input voltage cycle is surpassed, the output voltage will still remain due to the minimum off-time and minimum on-time limits in regulation, but the switching frequency will decrease of the regulator. The minimum off-time limit imposes a from its programmed value. Note that additional thermal maximum duty cycle which can be calculated as: derating may be applied. See the Thermal Considerations and Output Current Deratingand section in this data sheet. DMAX = 1 – tOFF(MIN) • fSW Rev. D For more information www.analog.com 9 Document Outline Features Applications Description Typical Application Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Decoupling Requirements Operation Applications Information Package Description Revision History Package Photo Design Resources Related Parts