LM5177DCPR datasheet(28/60 Pages) TI2

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This optional current sensing provides the capability to monitor or to limit either the input or the output current

of the DC/DC converter If the optional current sense amplifier is not used, the user can disable it to reduce the

bias current consumption of the whole device by connecting the IMONOUT pin to VCC. Do not do this dynamical

during the operation of the device because the configuration gets latched at start-up of the converter. Use the

CFG pin to select one of the following desired operation modes.

Current Monitor Operation:

In case the current sense amplifier is configured as a monitor, the output voltage on the IMONOUT pin is a linear

relation between the sense voltage between ISNSP and ISNSN pins and the sense amplifier transcendence as

well as the resistor placed on the IMONOUT pin:

VIMONOUT = VISNSP −VISNSN ×gm×RIMONOUT

(16)

The output voltage of the IMONOUT pin is clamped to the values given in specifications section.

If the user intends to reduce the bandwidth of the current monitor, the user can place an optional capacitor in

parallel to the IMONOUT pin like it is indicated in Figure 7-16.

Current Limit Operation:

In this configuration, the current sense gm amplifier monitors the voltage across the sense resistor and

compares it with an internal reference voltage. If the drop across the sense resistor is greater than the reference

threshold the gm amplifier gradually reduces the peak current capability of the DC/DC converter until the

differential voltage is equal the reference voltage. This function of the LM5177 can be used to do the following:

• Regulate the current into the load from the power stage

• Regulate the current from the output into the power stage

• Regulated the current from the input supply to the power stage

• Regulated the current into the device input from the power stage

To select a negative current limit direction, the SYNC pin needs to be pulled low for the time when EN/UVLO

goes above the EN rising threshold until the soft-start ramp starts the converter operation. The configuration gets

latched and the SYNC pin can be used for the synchronization afterward. If the synchronization function is not

used it can be pulled low continuously. For a positive current limit protection the SYNC pin can be pulled high or

connected to a valid synchronization signal during the time when EN/UVLO goes above the EN rising threshold

until the soft-start ramp starts the converter operation

Once the current limit operation mode is selected, a RC compensation network must be placed on the

IMONOUT pin. For most applications, a compensation bandwidth with a factor of 3× to 5× faster than the

compensation of the output voltage loop has given good results.

LM5177

SNVSBU4F – JUNE 2022 – REVISED JANUARY 2025

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LM5177DCPR Datasheet(PDF) 28 Page - Texas Instruments