LM2735XMFSLASHNOPB datasheet(11/59 Pages) TI

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1.6 MHz

VIN

ThermalSHDN

ILIMIT

NMOS

UVLO = 2.3V

ISENSE-AMP

Internal

Compensation

Soft-Start

Corrective - Ramp

Oscillator

Control Logic

VREF = 1.255V

GND

LM2735, LM2735-Q1

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SNVS485G – JUNE 2007 – REVISED AUGUST 2015

7.2 Functional Block Diagram

7.3 Feature Description

7.3.1 Current Limit

The LM2735 uses cycle-by-cycle current limiting to protect the internal NMOS switch. It is important to note that

this current limit will not protect the output from excessive current during an output short circuit. The input supply

is connected to the output by the series connection of an inductor and a diode. If a short circuit is placed on the

output, excessive current can damage both the inductor and diode.

7.3.2 Thermal Shutdown

Thermal shutdown limits total power dissipation by turning off the output switch when the IC junction temperature

exceeds 160°C. After thermal shutdown occurs, the output switch does not turn on until the junction temperature

drops to approximately 150°C.

7.3.3 Soft Start

This function forces VOUT to increase at a controlled rate during start-up. During soft start, the error amplifier’s

reference voltage ramps to its nominal value of 1.255 V in approximately 4 ms. This forces the regulator output to

ramp up in a more linear and controlled fashion, which helps reduce inrush current.

7.3.4 Compensation

The LM2735 uses constant-frequency peak current mode control. This mode of control allows for a simple

external compensation scheme that can be optimized for each application. A complicated mathematical analysis

can be completed to fully explain the internal and external compensation of the LM2735, but for simplicity, a

graphical approach with simple equations will be used. Below is a Gain and Phase plot of a LM2735 that

produces a 12-V output from a 5-V input voltage. The Bode plot shows the total loop Gain and Phase without

external compensation.

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