VOUT (5V/div)

IL (5A/div)

Overload

Release

Hiccup

20ms/div

12

LM5175

SNVSA37A – OCTOBER 2015 – REVISED MAY 2016

www.ti.com

Product Folder Links: LM5175

Submit Documentation Feedback

Copyright © 2015–2016, Texas Instruments Incorporated

Typical Characteristics (continued)

At TA = 25°C, unless otherwise stated.

VIN=24 V

VOUT=12 V

Hiccup Enabled

Figure 19. Hiccup Mode Current Limit

8 Detailed Description

8.1 Overview

The LM5175 is a wide input voltage four-switch buck-boost controller IC with integrated drivers for N-channel

MOSFETs. It operates in the buck mode when VIN is greater than VOUT and in the boost mode when VIN is less

than VOUT. When VIN is close to VOUT, the device operates in a proprietary transition buck or boost mode. The

control scheme provides smooth operation for any input/output combination within the specified operating range.

The buck or boost transition control scheme provides a low ripple output voltage when VIN equals VOUT without

compromising the efficiency.

The LM5175 integrates four N-Channel MOSFET drivers including two low-side drivers and two high-side drivers,

eliminating the need for external drivers or floating bias supplies. The internal VCC regulator supplies internal

bias rails as well as the MOSFET gate drivers. The VCC regulator is powered either from the input voltage

through the VIN pin or from the output or an external supply through the BIAS pin for improved efficiency.

The PWM control scheme is based on valley current mode control for buck operation and peak current mode

control for boost operation. The inductor current is sensed through a single sense resistor in series with the low-

side MOSFETs. The sensed current is also monitored for cycle-by-cycle current limit. The behavior of the

LM5175 during an overload condition is dependent on the MODE pin programming (see MODE Pin

Configuration). If hiccup mode fault protection is selected, the controller turns off after a fixed number of

switching cycles in cycle-by-cycle current limit and restarts after another fixed number of clock cycles. The hiccup

mode reduces the heating in the power components in a sustained overload condition. If hiccup mode is disabled

through the MODE pin, the controller remains in a cycle-by-cycle current limit condition until the overload is

removed. The MODE pin also selects continuous conduction mode (CCM) for noise sensitive applications or

discontinuous conduction mode (DCM) for higher light load efficiency.

In addition to the cycle-by-cycle current limiting, the LM5175 also provides an optional average current regulation

loop that can be configured for either input or output current limiting. This is useful for battery charging or other

applications where a constant current behavior may be required.

The soft-start time of LM5175 is programmed by a capacitor connected to the SS pin to minimize the inrush

current and overshoot during startup.

The precision EN/UVLO pin supports programmable input undervoltage lockout (UVLO) with hysteresis. The

output overvoltage protection (OVP) feature turns off the high-side drivers when the voltage at the FB pin is 7.5%

above the nominal 0.8-V VREF. The PGOOD output indicates when the FB voltage is inside a ±10% regulation

window centered at VREF.