LM5145 datasheet(23/55 Pages) TI

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driver has 1.5-Ω and 0.9-Ω pullup and pulldown impedances, respectively, for faster switching transition times,

lower switching loss, and greater efficiency.

The high-side gate driver works in conjunction with an integrated bootstrap diode and external bootstrap

capacitor, CBST. When the low-side MOSFET conducts, the SW voltage is approximately at 0 V and CBST is

charged from VCC through the integrated boot diode. Connect a 0.1-μF or larger ceramic capacitor close to the

BST and SW pins.

Furthermore, there is a proprietary adaptive dead-time control on both switching edges to prevent shoot-through

and cross-conduction, minimize body diode conduction time, and reduce body diode reverse recovery losses.

8.3.10 Current Sensing and Overcurrent Protection (ILIM)

The LM5146 implements a lossless current sense scheme designed to limit the inductor current during an

overload or short-circuit condition. Figure 8-8 portrays the popular current sense method using the on-state

resistance of the low-side MOSFET. Meanwhile, Figure 8-9 shows an alternative implementation with current

shunt resistor, RS. The LM5146 senses the inductor current during the PWM off-time (when LO is high).

VIN

VOUT

GND

ILIM

OUT

Figure 8-8. MOSFET RDS(on) Current Sensing

VIN

VOUT

GND

OUT

ILIM

Figure 8-9. Shunt Resistor Current Sensing

The ILIM pin of the LM5146 sources a reference current that flows in an external resistor, designated RILIM, to

program of the current limit threshold. A current limit comparator on the ILIM pin prevents further SW pulses if

the ILIM pin voltage goes below GND. Figure 8-10 shows the implementation.

Resistor RILIM is tied to SW to use the RDS(on) of the low-side MOSFET as a sensing element (termed RDS(on)

mode). Alternatively, RILIM is tied to a shunt resistor connected at the source of the low-side MOSFET (termed

RSENSE mode). The LM5146 detects the appropriate mode at start-up and sets the source current amplitude and

temperature coefficient (TC) accordingly.

The ILIM current with RDS-ON sensing is 200 µA at 27°C junction temperature and incorporates a TC of +4500

ppm/°C to generally track the RDS(on) temperature variation of the low-side MOSFET. Conversely, the ILIM

current is a constant 100 µA in RSENSE mode. This controls the valley of the inductor current during a steady-

state overload at the output. Depending on the chosen mode, select the resistance of RILIM using Equation 6.

OUT

DS(on)Q2

DS(on)

RDSON

ILIM

OUT

I 2

, R

sensing

I 2

R , shunt sensing

(6)

where

• ΔIL is the peak-to-peak inductor ripple current

• RDS(on)Q2 is the on-state resistance of the low-side MOSFET

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LM5146

SNVSBV0A – JUNE 2021 – REVISED JUNE 2021

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