LTC2977 datasheet(37/138 Pages) AD

37 / 138 page

LTM4664A

Rev. 0

For more information www.analog.com

the factory for details on efficient in-system EEPROM pro-

gramming, including bulk EEPROM Programming, which

the LTM4664A PSM also supports.

The LTM4664A PSM contains dual integrated constant fre-

quency current mode control buck regulators (channel 0

and channel 1) whose built-in power MOSFETs are capable

of fast switching speed. The factory NVM-default switching

frequency clocks SYNC at 350kHz, to which the regulators

synchronize their switching frequency. The default phase-in-

terleaving angle between the channels is 180°. A pin-strap-

ping resistor on FSWPH_CFG configures the frequency of

the SYNC clock (switching frequency) and the channel phase

relationship of the channels to each other and with respect

to the falling edge of the SYNC signal. (Most possible com-

binations of switching frequency and phase-angle assign-

ments are settable by resistor pin programming; see Table 3.

Configure the LTM4664A’s PSM NVM to implement settings

not available by resistor-pin strapping.) When a FSWPH_CFG

pin-strap resistor sets the channel phase relationship of the

LTM4664A’s PSM channels, the SYNC clock is not driven by

the module; instead, SYNC becomes strictly a high imped-

ance input and channel switching frequency is then synchro-

nized to SYNC provided by an externally-generated clock or

sibling LTM4664A with pull-up resistor to VDD33. Switching

frequency and phase relationship can be altered via the I2C

interface, but only when switching action is off, i.e., when the

module is not regulating either output. See the Dual 25A/30A

PSM Applications Information section for details.

Programmable analog feedback loop compensation for

channel 0 and channel 1 is accomplished with a capacitor

connection from COMP_C0a, 1a to SGND, and a capac-

itor from COMP_C0b, 1b to SGND.) The COMP_C0b, 1b

pin is for the high frequency gain roll off and is the gm

amplifier output that has a programmable range, and the

COMP_C0a, 1a pin has the programmable resistor range

along with a capacitor to SGND that sets the frequency

compensation. See Programmable Loop Compensation

section. The LTM4664A dual 25A/30A regulators module

have sufficient stability margins and good transient per-

formance with a wide range of output capacitors—even

all-ceramic MLCCs. Table 12 provides guidance on input

and output capacitors recommended for many common

operating conditions along with the programmable com-

pensation settings. The Analog Devices LTpowerCAD tool

is available for transient and stability analysis, and experi-

enced users who prefer to adjust the module’s feedback

loop compensation parameters can use this tool.

POWER-UP AND INITIALIZATION

The LTM4664A dual 25A/30A regulators are designed

to provide standalone supply sequencing and controlled

turn-on and turn-off operation. It operates from a single

input supply (4.5V to 16V) while three on-chip linear reg-

ulators generate internal 2.5V, 3.3V and 5.5V. The con-

troller configuration is initialized by an internal threshold

based UVLO where VIN must be approximately 4V and

the 5.5V, 3.3V and 2.5V linear regulators must be within

approximately 20% of the regulated values. In addition

to the power supply, a PMBus RESTORE_USER_ALL or

MFR_RESET command can initialize the part too.

The EXTVCC pin is driven by an external regulator to

improve efficiency of the circuit and minimize power loss

when VINS3 is high. The EXTVCC pin must exceed approx-

imately 4.7V, and VINS3 must exceed approximately 7V

before the INTVCC LDO operates from the EXTVCC pin.

To minimize application power, the EXTVCC pin can be

supplied by a switching regulator.

During initialization, the external configuration resistors

are identified and/or contents of the NVM are read into the

controller’s commands and the power train is held off. The

RUN_Cn and FAULT_Cn and PGOOD_Cn are held low. The

LTM4664A dual 25A/30A regulators will use the contents

of Table 1 thru Table 5 to determine the resistor defined

parameters. See the Resistor Configuration section for more

details. The resistor configuration pins only control some

of the preset values of the controller. The remaining values

are programmed in NVM either at the factory or by the user.

If the configuration resistors are not inserted or if the ignore

RCONFIG bit is asserted (bit 6 of the MFR_CONFIG_ALL

configuration command), the LTM4664A PSM will use

only the contents of NVM to determine the DC/DC char-

acteristics. The ASEL value read at power-up or reset is

always respected unless the pin is open. The ASEL will set

the bottom 4LSBs and the MSBs are set by NVM. See the

Dual 25A/30A PSM Applications Information section for

more details.

DUAL 25A/30A PSM OPERATION

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