LTM4650A datasheet(20/36 Pages) AD

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LTM4671

Rev. B

For more information www.analog.com

Figure 6. Output Coincident Tracking Waveform

4671 F06

TIME

VOUT0 = 1.0V

VOUT3 = 1.2V

VOUT2 = 2.5V

VOUT1 = 3.3V

RFB(SL)

RFB(SL) + 60.4k

RTR(BOT)

RTR(TOP) + RTR(BOT)

From the equation, we could easily find out that, in the

coincident tracking, the slave regulator’s TRACK/SS pin

resistor divider is always the same as its feedback divider.

For example, RTR(TOP)3 = 60.4k and RTR(BOT)3 = 60.4k

is a good combination for coincident tracking for

VOUT(MA) = 3.3V and VOUT(SL) =1.2V application.

POWER GOOD

The PGOOD pins are open-drain pins that can be used to

monitor valid output voltage regulation. This pin monitors

a ±10% window around the regulation point. A resistor

can be pulled up to a particular supply voltage for moni-

toring. To prevent unwanted PGOOD glitches during tran-

sients or dynamic VOUT changes, the LTM4671’s PGOOD

falling edge includes a blanking delay of approximately

52 switching cycles.

STABILITY COMPENSATION

The LTM4671 module internal compensation loop of each

regulator channel is designed and optimized for low ESR

ceramic output capacitors only application (COMPb tied

to COMPa for 12A channels). Table 3 is provided for most

application requirements using the optimized internal

compensation. In case of all ceramic output capacitors

is required for output ripples or dynamic transient spike

reduction, an additional 10pF to 15pF phase boost cap is

required between VOUT and FB pins.

For specific optimized requirement for the dual 12A chan-

nels, disconnect COMPb from COMPa and apply a Type II

C-R-C compensation network from COMPa to SGND to

achieve external compensation.

The LTpowerCAD design tool is available to download

online to perform specific control loop optimization and

analyzethecontrolstabilityandloadtransientperformance.

RUN ENABLE

Pulling the RUN pin of each regulator channel to ground

forcestheregulatorintoitsshutdownstate,turningoffboth

power MOSFETs and most of its internal control circuitry.

Bringing the RUN pin above 0.7V turns on the internal

reference only, while still keeping the power MOSFETs

off. Further increasing the RUN pin voltage above 1.2V

will turn on the entire regulator channel.

TEMPERATURE MONITORING

The 12A Channels (CH0, CH3):

Measuring the absolute temperature of a diode is pos-

sible due to the relationship between current, voltage

and temperature described by the classic diode equation:

ID = IS •e

η • VT

⎛

⎝⎜

⎞

⎠⎟

VD = η • VT •In

where ID is the diode current, VD is the diode voltage, η

is the ideality factor (typically close to 1.0) and IS (satu-

ration current) is a process dependent parameter. VT can

be broken out to:

VT =

k • T

APPLICATIONS INFORMATION

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