TLE8366

Buck Regulator

Data sheet

7

Rev. 1.0, 2009-05-18

5

Buck Regulator

5.1

Description

5.1.1

Arrangement

The step-down (or buck) regulator consists of several functional blocks, which shall be explained in the following:

The oscillator, the regulator, the safety functions, the gate driver and the internal MOSFET.

5.1.1.1

Regulator Block

The oscillator creates a saw-tooth signal, which is supplied to the PWM comparator and the Schmitt-Trigger 1. The

frequency of the oscillator might be synchronized to an external frequency connected to pin sync.

The Error Amplifier compares the feedback signal to the reference voltage. At the variable voltage version the

feedback pin shall be connected to an external resistor divider, the fixed voltage versions contain an internal

resistor divider. The soft start function is included by the ramp generator between the reference voltage source

and the error amplifier. It generates a defined ramp after the initialization of the device. (The device is initialized

after signal EN turns to high (with supply voltage at VS present) or with rising Supply voltage (with EN = H

connected to VS) or at restarting after a thermal shutdown. The ramp starts, if the Buck Driver Supply (BDS)

external capacitor is charged.

Only for the variable voltage version: If the feedback signal at pin FB gets lost, an internal pull-up current source

will pull the pin too high thus preventing the output voltage from overshooting.

A compensation network needs to be connected to the output of the error amplifier using pin COMP.

The PWM comparator creates the Pulse-Width Modulated (PWM) signal by comparing the error amplifier output

with the saw-tooth signal from the oscillator.

5.1.1.2

Safety Functions Block

The safety functions block consists of the Error-Flip Flop, the Nor1 Gate and the PWM-Flip-Flop.

The Error Flip-Flop collects the failure events such as the over-current shutdown of the internal MOSFET, the

output overvoltage shutdown and the temperature shutdown.

The over-current shutdown signal is created by the OC comparator. It detects the voltage across an internal shunt

resistor. If the current exceeds the reference level, the pulse is shut down and the MOSFET switched off.

The bootstrap under-voltage shutdown is created by the BDS UV comparator, which compares the bootstrap

capacitor voltage to a reference level. If the bootstrap capacitor voltage is too low, the pulse will be shut down and

the MOSFET switched off.

If the output voltage exceeds a reference value, the pulse will also be shut down and the MOSFET switched off.