LTM4608V 查看數據表（PDF） - Linear Technology

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LTM4608V

Low VIN, 8A DC/DC µModule Regulator with Tracking, Margining, and Frequency Synchronization

Linear Technology 

LTM4608

OPERATION

Current mode control provides cycle-by-cycle fast current

limit and thermal shutdown in an overcurrent condition.

Internal overvoltage and undervoltage comparators pull

the open-drain PGOOD output low if the output feedback

voltage exits a ±10% window around the regulation point.

Pulling the RUN pin below 1.3V forces the controller into

its shutdown state, by turning off both M1 and M2 at low

load current. The TRACK pin is used for programming the

output voltage ramp and voltage tracking during start-up.

See Applications Information.

The LTM4608 is internally compensated to be stable over

all operating conditions. Table 3 provides a guideline

for input and output capacitances for several operating

conditions. The Linear Technology µModule Power De-

sign Tool is provided for transient and stability analysis.

The FB pin is used to program the output voltage with a

single external resistor to ground.

Multiphase operation can be easily employed with the

synchronization and phase mode controls. Up to 12 phases

can be cascaded to run simultaneously with respect to

each other by programming the PHMODE pin to different

levels. The LTM4608 has clock in and clock out for poly

phasing multiple devices or frequency synchronization.

High efficiency at light loads can be accomplished with

selectable Burst Mode operation using the MODE pin. These

light load features will accommodate battery operation.

Efficiency graphs are provided for light load operation in

the Typial Performance Characteristics.

Output voltage margining is supported, and can be pro-

gramed from ±5% to ±15% using the MGN and BSEL pins.

The PGOOD pin is disabled during margining.

APPLICATIONS INFORMATION

The typical LTM4608 application circuit is shown in Fig-

ure 18. External component selection is primarily deter-

mined by the maximum load current and output voltage.

Refer to Table 3 for specific external capacitor requirements

for a particular application.

VIN to VOUT Step-Down Ratios

There are restrictions in the maximum VIN to VOUT step-

down ratio that can be achieved for a given input voltage.

The LTM4608 is 100% duty cycle, but the VIN to VOUT

minimum dropout is a function of its load current. Please

refer to the curves in the Typical Performance Charac-

teristics section of this data sheet for more information.

Output Voltage Programming

The PWM controller has an internal 0.596V reference

voltage. As shown in the Block Diagram, a 10k/0.5%

internal feedback resistor connects VOUT and FB pins

together. The output voltage will default to 0.596V with

no feedback resistor. Adding a resistor RFB from FB pin

to GND programs the output voltage:

VOUT

=

0.596V

•

10k + RFB

RFB

10

Table 2. RFB Resistor vs Output Voltage

VOUT 0.596V 1.2V 1.5V 1.8V

RFB Open 10k 6.65k 4.87k

2.5V

3.09k

3.3V

2.21k

Input Capacitors

The LTM4608 module should be connected to a low AC

impedance DC source. Three 10µF ceramic capacitors

are included inside the module. Additional input capaci-

tors are only needed if a large load step is required up to

the 4A level. A 47µF to 100µF surface mount aluminum

electrolytic bulk capacitor can be used for more input bulk

capacitance. This bulk input capacitor is only needed if

the input source impedance is compromised by long in-

ductive leads, traces or not enough source capacitance.

If low impedance power planes are used, then this 47µF

capacitor is not needed.

For a buck converter, the switching duty-cycle can be

estimated as:

D=

VOUT

VIN

4608fc

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