LTM4607 datasheet(14/28 Pages) LINER

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LTM8056

8056fa

For more information www.linear.com/LTM8056

above information and the circuit shown in Figure 2, the

VIN rising (turn-on) threshold is:

VIN = 3µA •R1

(

)+1.225V

R1+R2

and the VIN falling turn-off threshold is:

VIN =1.2

R1+R2

when the voltage VOUT-IOUT reaches 58mV. The current

limit is:

IOUT(LIM) =

58mV

RSENSE

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

Most applications should use an output sense resistor as

shown in Figure 3, if practical. The internal buck-boost

power stage is current limited, but is nonetheless capable

of delivering large amounts of current in an overload

condition, especially when the output voltage is much

lower than the input and the power stage is operating as

a buck converter.

APPLICATIONS INFORMATION

RUN

LTM8056

VIN

8056 F02

Figure 2. This Simple Resistor Network Sets the Minimum

Operating Input Voltage Threshold with Hysteresis

IOUT

LTM8056

VOUT

RSENSE

8056 F03

LOAD

Figure 3. Set The LTM8056 Output Current Limit with an

External Sense Resistor

Minimum Input Voltage and SVIN

The minimum input voltage of the LTM8056 is 5V, but this

is only if VIN and SVIN are tied to the same voltage source.

If SVIN is powered from a power source at or above 5VDC,

VIN can be allowed to fall below 5V and the LTM8056 can

still operate properly. Some examples of this are provided

in the Typical Applications section.

Soft-Start

Soft-startreducestheinputpowersources’surgecurrents

bygraduallyincreasingthecontroller’scurrent.Asindicated

in the Block Diagram, the LTM8056 has an internal soft-

start RC network. Depending upon the load and operating

conditions, the internal network may be sufficient for the

application. To increase the soft-start time, simply add a

capacitor from SS to GND.

Output Current Limit (IOUT)

The LTM8056 features an accurate average output current

limit set by an external sense resistor placed between VOUT

and IOUT as shown in Figure 3. VOUT and IOUT internally

connect to a differential amplifier that limits the current

When the voltage across the output sense resistor falls

to about 1/10th of full scale, the LL pin pulls low. If there

is no output sense resistor, and IOUT is tied to VOUT, LL

will be active low. Applying an output sense resistor and

tying the LL and MODE pins together can improve perfor-

mance—see Switching Mode in this section.

In high step-down voltage regulator applications, the

internal current limit can be quite high to allow proper

operation. This can potentially damage the LTM8056

in overload or short-circuit conditions. Apply an output

current sense resistor to set an appropriate current limit

to protect the LTM8056 against these fault conditions.

Output Current Limit Control (CTL)

Use the CTL input to reduce the output current limit from

thevaluesetbytheexternalsenseresistorappliedbetween

VOUT and IOUT. The typical control range is between 0V

and 1.2V. The CTL pin does not directly affect the input

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