LM5177DCPR datasheet(18/60 Pages) TI2

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7 Detailed Description

7.1 Overview

The LM5177 is a four switch buck-boost controller. The device provides a regulated output voltage if the input

voltage is higher, equal, or lower than the adjusted output voltage.

In power save mode, the LM5177 supports superb efficiency over the full rage of the output current. The

operation modes are on-the-fly pin-selectable during operation. The proprietary buck-boost modulation scheme

also runs at a fixed switching frequency, which can be set through the RT/SYNC pin. The switching frequency

remains constant during buck, boost, and buck-boost operation. The device maintains small mode transition

ripple over all operating modes. Through the activation of the dual random spread spectrum operation, EMI

mitigation is achievable at any time of the design process.

The integrated and optional average current monitor can help monitor or limit input and output current of the

LM5177. This feature also supports charging backup power elements, like batteries with constant current (CC)

and constant voltage (CV).

The output voltage of the LM5177 can be dynamically adjusted during operation (dynamic voltage scaling and

envelope tracking). The adjustment is either possible by changing the analog reference voltage of the SS/ATRK

pin or it can be done directly with a PWM input signal on the DTRK pin.

The internal wide input LDOs ensure a robust supply of the device functionality under different input and

output voltage conditions. Due to the high drive capability and the automatic and headroom depended voltages

selection, the power losses are kept at a minimum at high switching frequency operation. The separate bias pin

can be connected to the input, output, or an external supply to further reduce power losses in the device. At all

times, the internal supply voltage is monitored to avoid undefined failure handling.

The LM5177 integrates a full bridge N-channel MOSFET driver. The gate driver circuit has a high driving

capability to ensure high efficiency targets over the wide range of the supported application. The gate driver

features an integrated high voltage low dropout bootstrap diode. The internal bootstrap circuit has a protection

against an overvoltage that can be injected by negative spikes and an undervoltage lockout protection to avoid

a linear operation of the external power FET. The bootstrap circuit ensures 100% duty cycle operation in pure

boost or buck mode.

The resistor-to-digital (R2D) interface offers the user a simple and robust selection of all the device functionality

where the analog settings of the soft start minimize the inrush current. Additionally, the control loop and slope

compensation ensure a best-in-class output performance for the wide range of supported application cases.

The devices built-in protection features ensure a safe operation under different fault conditions. There is a VIN

undervoltage lockout protection to avoid brownout situations. Because the input UVLO threshold and hysteresis

can be configured through an external feedback divider, the brownout is avoided under the different designs.

The device has an output overvoltage protection and an input overvoltage protection for negative current

operation. The selectable hiccup overcurrent protection avoids excessive short circuit currents by using the

internal cycle-by-cycle peak current protection. Due to the integrated thermal shutdown, the device is protected

against thermal damage caused by an overload condition of the internal VCC regulators. All output-related fault

events are monitored and indicated at the open-drain nFLT pin of the device.

7.2 Functional Block Diagram

7.3 Feature Description

7.3.1 Power-On Reset (POR System)

The integrated power-on reset system supplies all internal functional circuits other than the gate drivers and

handles the supervision for the internal logic. The low quiescent current design of this block enables an

extremely low shutdown current of the whole system. There is a power ORing between the VIN and BIAS

pin for the POR system to ensure LM5177 functionality even under extreme operation conditions, like an output

or input short.

LM5177

SNVSBU4F – JUNE 2022 – REVISED JANUARY 2025

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