Datasheet LTM4668A (Analog Devices) - 9

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DECOUPLING REQUIREMENTS SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS Switching Regulator Section: (Per Channel)
CIN External Input Capacitor Requirement IOUT = 1.2A 4.7 10 µF (VIN = 2.7V to 17V, VOUT = 1.5V) COUT External Output Capacitor Requirement IOUT = 1.2A 22 47 µF (VIN = 2.7V to 17V, VOUT = 1.5V)
OPERATION
The LTM4668A is a quad output standalone non-isolated Current mode control also provides cycle-by-cycle fast switch mode DC/DC power supply. It has built-in four overcurrent protection. An internal overvoltage and separate regulator channels and each of them can deliver undervoltage comparator pulls the open-drain PGOOD 1.2A continuous output current with few external input output low if the output feedback voltage exits a ±7.5% and output capacitors. Each regulator provides precisely window around the regulation point. Furthermore, in an regulated output voltage programmable via a single exter- overvoltage condition, internal top FET is turned off and nal resistor over 2.7V to 17V input voltage range. The bottom FET is turned on and held on until the overvoltage LTM4688A supports output voltages of 0.6V to 5.5V. The condition clears. typical application schematic is shown in Figure 14. Pulling the RUN pin below 0.35V forces the controller The LTM4668A uses a constant frequency, peak current into its shutdown state, turning off both power MOSFETs mode architecture and has integrated power MOSFETs, and most of the internal control circuitry. At light load inductors, and other supporting discrete components. currents, pulse-skipping mode or Burst Mode operation The typical switching frequency is set to 2.25MHz. For can be enabled to achieve higher efficiency compared to switching noise-sensitive applications, the µModule can continuous mode (CCM) by setting MODE/SYNC pin to be externally synchronized to a clock from 1.5MHz to GND or INTVCC accordingly. The LTM4668A has internal 3MHz. See the Applications Information section. 800µs soft-start ramp on each output channel. With current mode control and internal feedback loop The pin compatible part LTM4668 is recommended when compensation, the LTM4668A module has sufficient sta- operating at a lower output voltage range of 0.6V to 1.8V bility margins and good transient performance with a wide and has a typical switching frequency of 1MHz. The dif- range of output capacitors, even with all ceramic output ferences between LTM4668 and LTM4668A are shown capacitors. in Table 1. Current mode control provides the flexibility of parallel-
Table 1.
ing any of the separate regulator channels with accurate
RECOMMENDED VOUT RANGE SWITCHING FREQUENCY
current sharing. With a built-in clock interleaving between LTM4668 0.6V to 1.8V 1MHz each two regulator channels, the LTM4668A could easily LTM4668A 0.6V to 5.5V* 2.25MHz employ a 2+2, 3+1 or all 4 channels, parallel operation *There are restrictions in the maximum V which is more than flexible in a multi-rail POL application. IN and VOUT step-down ratio. See VIN to VOUT Step-Down Ratios section. Rev. A For more information www.analog.com 9 Document Outline Features Applications Typical Application Description Absolute Maximum Ratings Order Information Pin Configuration Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Decoupling Requirements Operation Applications Information Typical Applications Package Description Revision History Package Photo Design Resources Related Parts