LTM4607 datasheet(15/28 Pages) LINER

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LTM8056

8056fa

For more information www.linear.com/LTM8056

current limit. If this function is not used, leave CTL open.

Drive CTL to less than about 50mV to stop switching. The

CTL pin has an internal pull-up resistor to 2V.

Input Current Limit (IIN)

SomeapplicationsrequirethattheLTM8056drawnomore

than some predetermined current from the power source.

Current limited power sources and power sharing are two

examples.TheLTM8056featuresanaccurateinputcurrent

limit set by an external sense resistor placed between IIN

and VINasshowninFigure4.VINandIINinternallyconnect

to a differential amplifier that limits the current when the

voltage IIN-VIN reaches 50mV. The current limit is:

IIN(LIM) =

50mV

RSENSE

where RSENSE is the value of the sense resistor in ohms.

If input current limiting is not required, simply tie IINtoVIN.

Synchronization

TheLTM8056switchingfrequencycanbesynchronizedto

an external clock using the SYNC pin. Driving SYNC with

a 50% duty cycle waveform is a good choice, otherwise

maintainthedutycyclebetweenabout10%and90%.When

synchronizing, a valid resistor value (that is, a value that

results in a free-running frequency of 100kHz to 800kHz)

must be connected from RT to GND.

While an RT resistor is required for proper operation, the

value of this resistor is independent of the frequency of

the externally applied SYNC signal. Be aware, however,

that the LTM8056 will switch at the frequency prescribed

by the RT value if the SYNC signal terminates, so choose

an appropriate resistor value.

CLKOUT

The CLKOUT signal reflects the internal switching clock of

theLTM8056.Itisphaseshiftedbyapproximately180°with

respect to the leading edge of the internal clock. If CLKOUT

is connected to the SYNC input of another LTM8056, the

two devices will switch about 180° out of phase.

Input Precaution

In applications where the output voltage is deliberately

pulled up above the set regulation voltage or the FB pin is

abruptlydriventoanewvoltage,theLTM8056mayattempt

to regulate the voltage by removing energy from the load

for a short period of time after the output is pulled up.

Since the LTM8056 is a synchronous switching converter,

it delivers this energy to the input. If there is nothing on the

LTM8056 input to consume this energy, the input voltage

may rise. If the input voltage rises without intervention, it

may rise above the absolute maximum rating, damaging

the part. Carefully examine the input voltage behavior to

see if the application causes it to rise.

In many cases, the system load on the LTM8056 input

bus will be sufficient to absorb the energy delivered by the

μModule regulator. The power required by other devices

will consume more than enough to make up for what

APPLICATIONS INFORMATION

Figure 4. Set the LTM8056 Input Current Limit with an External

Sense Resistor

IIN

LTM8056

RSENSE

VIN

POWER

SOURCE

8056 F04

Input Current Monitor (IINMON)

The IINMON pin produces a voltage equal to approximately

20 times the voltage of IIN-VIN. Since the LTM8056 input

current limit engages when IIN-VIN = 50mV, IINMON will

be 1V at maximum input current.

Output Current Monitor (IOUTMON)

The IOUTMON pin produces a voltage proportional to the

voltage of VOUT-IOUT. Since the LTM8056 output current

limit engages when VOUT-IOUT = 58mV, IOUTMON will be

1.2V at maximum output current.

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