Datasheet LTM4622 (Analog Devices) - 9

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OPERATION
The LTM4622 is a dual output standalone non-isolated stability margins and good transient performance with switch mode DC/DC power supply. It can deliver two 2.5A a wide range of output capacitors, even with all ceramic DC, 3A peak output current with few external input and output capacitors. output ceramic capacitors. This module provides dual Current mode control provides cycle-by-cycle fast cur- precisely regulated output voltage programmable via rent limiting. An internal overvoltage and undervoltage two external resistor from 0.6V to 5.5V over 3.6V to 20V comparators pull the open-drain PGOOD output low if input voltage range. With INTVCC tied to VIN, this module the output feedback voltage exits a ±8% window around is able to operate from 3.3V input. The typical application the regulation point. Furthermore, an input overvoltage schematic is shown in Figure 24. protection been utilized by shutting down both power The LTM4622 contains an integrated controlled on-time MOSFETs when VIN rises above 22.5V to protect internal valley current mode regulator, power MOSFETs, inductor, devices. and other supporting discrete components. The default Multiphase operation can be easily employed by connect- switching frequency is 1MHz. For output voltages between ing SYNC pin to an external oscillator. Up to 6 phases can 2.5V and 5.5V, an external resistor is required between be paralleled to run simultaneously a good current sharing FREQ and GND pins to set the operating frequency to guaranteed by current mode control loop. higher frequency to optimize inductor current ripple. For switching noise-sensitive applications, the switch- Pulling the RUN pin below 1V forces the controller into ing frequency can be adjusted by external resistors and its shutdown state, turning off both power MOSFETs and the μModule regulator can be external y synchronized most of the internal control circuitry. At light load cur- to a clock within ±30% of the set frequency. See the rents, Burst Mode operation can be enabled to achieve Applications Information section. higher efficiency compared to continuous mode (CCM) by setting MODE pin to INTV With current mode control and internal feedback loop CC. The TRACK/SS pin is used for power supply tracking and soft-start programming. compensation, the LTM4622 module has sufficient See the Applications Information section.
APPLICATIONS INFORMATION
The typical LTM4622 application circuit is shown in where tOFF(MIN) is the minimum off-time, 45ns typical for Figure 24. External component selection is primarily deter- LTM4622, 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 7 for specific exter- cycle of the converter which can be calculated as nal capacitor requirements for a particular application. DMIN = tON(MIN) • fSW
V
where tON(MIN) is the minimum on-time, 20ns typical for
IN to VOUT Step-Down Ratios
LTM4622. In the rare cases where the minimum duty There are restrictions in the maximum VIN and VOUT step cycle is surpassed, the output voltage will still remain down ratio that can be achieved for a given input voltage in regulation, but the switching frequency will decrease due to the minimum off-time and minimum on-time limits from its programmed value. Note that additional thermal of the regulator. The minimum off-time limit imposes a derating may be applied. See the Thermal Considerations maximum duty cycle which can be calculated as and Output Current Derating section in this data sheet. DMAX = 1 – tOFF(MIN) • fSW Rev. H For more information www.analog.com 9 Document Outline Features Applications Typical Application Description Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Decoupling Requirements Operation Applications Information Safety Considerations Layout Checklist/Example Package Description Revision History Package Photo Design Resources Related Parts