TLD5085EJ_1 Datasheet, PDF (7/16 Pages) Infineon Technologies AG – 1.8A DC/DC Step-Down Converter

TLD5085EJ
Buck Regulator
5
Buck Regulator
5.1
Description
The gate of the power-switch is driven by the Gate driver which is supplied by the external capacitor connected to
pin BDS (Buck Driver Supply) using the bootstrap principle.
BDS is the supply pin for the integrated gate driver of the internal power-switch. The power-switch has to be in the
R_DSon region. If V_GS is not high enough, the power-switch can not operate in the R_DSON region, which means high
power dissipation. An integrated under voltage lockout function (BDS UV-Comparator) supervising the ’bootstrap’
capacitor voltage ensures that the device is always driven with a sufficient bootstrap voltage in order to prevent
from extensive heat up of the power-switch.
An integrated charge pump supports the gate driver in case of low input supply voltage, small differential voltage
between input supply and output voltage at low current and during startup. In order to minimize emission, the
charge pump is switched off if the input voltage is sufficient for supplying the bootstrap.
The soft start function generates a defined ramp of the reference voltage during the first 0.5 ms (typ.) after device
initialization and if the Device is autorestarting after a thermal shutdown. This function is disabled during the
dimming operation via the PWMI-pin.
VS 8
COMP 3
Overcurrent
Comp.
FB 4
Feedback
Error Amp.
Soft Start
Ramp
PWM
Comp.
= _{VREF=0.6 V}
Ramp Generator
Clock
Logic
Charge
Pump
BDS
Charger
Gate
Driver
Temp.
Sensor
BDS
UV Comp.
2
GND
1
PWMI
Figure 3 Block Diagram Buck Regulator
5 BDS
Power
Switch
6 BUO
Datasheet
7
Rev. 1.1, 2009-12-16