Datasheet LTM4622A (Analog Devices) - 9

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OPERATION
The LTM4622A is a dual output standalone non-isolated a wide range of output capacitors, even with all ceramic switch mode DC/DC power supply. It can deliver two 2A output capacitors. DC, 3A peak output current with few external input and Current mode control provides cycle-by-cycle fast cur- output ceramic capacitors. This module provides dual rent limiting. An internal overvoltage and undervoltage precisely regulated output voltage programmable via two comparators pull the open-drain PGOOD output low if the external resistor from 1.5V to 12V over 3.6V to 20V input output feedback voltage exits a ±8% window around the voltage range. The typical application schematic is shown regulation point. Furthermore, an input overvoltage protec- in Figure 27. tion been utilized by shutting down both power MOSFETs The LTM4622A contains an integrated controlled on-time when VIN rises above 22.5V to protect internal devices. valley current mode regulator, power MOSFETs, inductors, Multiphase operation can be easily employed by connecting and other supporting discrete components. The default SYNC pin to an external oscillator. Up to 6 phases can be switching frequency is 1MHz. For output voltages above paralleled to run simultaneously a good current sharing 3.3V, an external resistor is required between FREQ and guaranteed by current mode control loop. GND pins to set the operating frequency to 1.5MHz to 2MHz to optimize inductor current ripple. For switching Pulling the RUN pin below 1V forces the controller into noise-sensitive applications, the switching frequency can its shutdown state, turning off both power MOSFETs and be adjusted by external resistors and the μModule regulator most of the internal control circuitry. At light load currents, can be externally synchronized to a clock within ±30% of Burst Mode operation can be enabled to achieve higher the set frequency. See the Applications Information section. efficiency compared to continuous mode (CCM) by set- ting 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. See compensation, the LTM4622A module has sufficient the Applications Information section. stability margins and good transient performance with
APPLICATIONS INFORMATION
The typical LTM4622A application circuit is shown in where tOFF(MIN) is the minimum off-time, 45ns typical for Figure  27. External component selection is primarily LTM4622A, and fSW is the switching frequency. Conversely determined by the input voltage, the output voltage and the minimum on-time limit imposes a minimum duty cycle the maximum load current. Refer to Table 7 for specific of the converter which can be calculated as: external capacitor requirements for a particular application. DC(MIN) = tON(MIN) • fSW
V
where tON(MIN) is the minimum on-time, 20ns typical for
IN to VOUT Step-Down Ratios
LTM4622A. 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. DC(MAX) = 1 – tOFF(MIN) • fSW Rev B 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 Package Photos Design Resources Related Parts