LTM4607 datasheet(7/28 Pages) LINER

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LTM8056

8056fa

For more information www.linear.com/LTM8056

TYPICAL PERFORMANCE CHARACTERISTICS

Maximum Output Current vs CTL

Voltage DC2154A Demo Board,48VIN

Soft-Start Waveforms for Various

CSS Values 24VIN, 3A Resistive

Load, DC2154A Demo Board

Output Ripple, Stock DC2154A

Demo Board, 24VOUT

TA = 25°C, unless otherwise noted.

PIN FUNCTIONS

GND(Bank1,PinL1):TietheseGNDpinstoalocalground

plane below the LTM8056 and the circuit components.

In most applications, the bulk of the heat flow out of the

LTM8056 is through these pads, so the printed circuit

design has a large impact on the thermal performance of

the part. See the PCB Layout and Thermal Considerations

sections for more details. Return the RFB1/RFB2 feedback

divider to this net.

VOUT (Bank 2): Power Output Pins. Apply output filter

capacitors between these pins and GND pins.

VIN (Bank 3): Input Power. The VIN pin supplies current to

theLTM8056’sinternalpowerswitchesandtooneterminal

of the optional input current sense resistor. This pin must

be locally bypassed with an external, low ESR capacitor;

see Table 1 for recommended values.

IOUT (Pin D1): Output Current Sense. Tie this pin to the

output current sense resistor. The output average current

sense threshold is 58mV, so the LTM8056 will regulate

the output current to 58mV/RSENSE, where RSENSE is the

value of the output current sense resistor in ohms. The

load is powered through the sense resistor connected at

this pin. Tie this pin to VOUT if no output current sense

resistor is used. Keep this pin within ±0.5V of VOUT under

all conditions.

LL (Pin F1): Light Load Indicator. This open drain pin

indicates that the output current, as sensed through the

resistor connected between VOUT and IOUT, is approxi-

mately equivalent to 6mV or less. Its state is meaningful

only if a current sense resistor is applied between VOUT

and IOUT. This is useful to change the switching behavior

of the LTM8056 in light load conditions.

SVIN (Pins F10, F11): Controller Power Input. Apply a

separate voltage above 5V if the LTM8056 is required to

operate when the main power input (VIN) is below 5V.

Bypass these pins with a high quality, low ESR capacitor.

If a separate supply is not used, connect these pins to VIN.

CLKOUT (Pin G1): Clock Output. Use this pin as a clock

source when synchronizing other devices to the switch-

ing frequency of the LTM8056. When this function is not

used, leave this pin open.

MODE (Pin G2): Switching Mode Input. The LTM8056

operates in forced continuous mode when MODE is

open, and can operate in discontinuous switching mode

when MODE is low. In discontinuous switching mode,

the LTM8056 will block reverse inductor current. This pin

is normally left open or tied to LL. This pin may be tied

to GND for the purpose of blocking reverse current if no

output sense resistor is used.

CTL VOLTAGE (V)

8056 G28

1.4

0.4

0.7

1.1

VOUT

5V/DIV

8056 G29

500µs/DIV

CSS = 22nF

CSS = 100nF

CSS = 220nF

24VIN, 3A LOAD

(BUCK-B00ST),

100mV/DIV

48VIN, 3A LOAD

(Buck),

100mV/DIV

12VIN, 1.5A LOAD

(B00ST),

100mV/DIV

MEASURED ACROSS C17 ON DC2154A WITH HP461

AMPLIFIER, 150MHz BANDWIDTH

8056 G30

1µs/DIV

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