LM5045MHXSLASHNOPB.A datasheet(5/47 Pages) TI2

5 / 47 page

LM5045

www.ti.com

SNVS699H – FEBRUARY 2011 – REVISED JANUARY 2015

Pin Functions (continued)

I/O

DESCRIPTION

APPLICATION INFORMATION

NAME

HTSSOP

WQFN

Synchronous Rectifier

Control output for synchronous rectifier gate. Capable of

SR1

Driver

peak sourcing 100 mA and sinking 400 mA.

Synchronous Rectifier

Control output for synchronous rectifier gate. Capable of

SR2

Driver

peak sourcing 100 mA and sinking 400 mA.

An internal 20-µA current source charges the SS pin during

start-up. The input to the PWM comparator gradually rises as

the SS capacitor charges to steadily increase the PWM duty

Soft-Start Input

cycle. Pulling the SS pin to a voltage below 20 0mV stops

PWM pulses at HO1, 2 and LO1, 2 and turns off the

synchronous rectifier FETs to a low state.

When SS OFF pin is connected to the AGND, the LM5045

soft-stops in the event of a VIN UVLO and Hiccup mode

SSOFF

Soft-Stop Disable

current limit condition. If the SSOFF pin is connected to REF

pin, the controller hard-stops on any fault condition. Refer to

Table 1 for more details.

An external capacitor and an internal 20-µA current source

set the soft-start ramp for the synchronous rectifiers. The

SSSR

Secondary Side Soft-Start

SSSR capacitor charge-up is enabled after the first output

pulse and SS > 2 V and Icomp < 800 µA

An external voltage divider from the power source sets the

shutdown and standby comparator levels. When UVLO

reaches the 0.4-V threshold the VCC and REF regulators are

Line Undervoltage

UVLO

enabled. At the 1.25-V threshold, the SS pin is released and

Lockout

the controller enters the active mode. Hysteresis is set by an

internal current sink that pulls 20 µA from the external

resistor divider.

The output voltage of the start-up regulator is initially

regulated to 9.5 V. Once the secondary side soft-start (SSSR

Output of Start-Up

pin) reaches 1 V, the VCC output is reduced to 7.7 V. If an

VCC

Regulator

auxiliary winding raises the voltage on this pin above the

regulation set-point, the internal start-up regulator will

shutdown, thus reducing the IC power dissipation.

Input to the Start-up Regulator. Operating input range is 14 V

to 100 V. For power sources outside of this range, the

VIN

Input Power Source

LM5045 can be biased directly at VCC by an external

regulator.

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