TLE6389_07 datasheet(26/38 Pages) INFINEON

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TLE 6389

Datasheet Rev. 2.1

2007-08-13

The ON-trigger is set periodically by the internal oscillator when acting in PWM mode

and is given by the output of the WAKE-comparator when operating in PFM mode. The

Multiplexer (MUX) is switched by the output of the MODE-detector which distinguishes

between PFM and PWM by tracking the output voltage (goto PFM) and by tracking the

gate trigger frequency (goto PWM). In PFM mode the peak current limit is reduced to

prevent overshoots at the output of the buck regulator. In order to avoid a gate turn off

signal due to the current peak caused by the parasitic capacitance of the catch diode the

blanking filter is necessary. The blanking time is set internally to 200ns and determines

(together with the PMOS turn on and turn off delay) the minimum duty cycle of the

device. In addition to the PFM/PWM regulation scheme an overvoltage lockout and

thermal protection are implemented to guarantee safe operation of the device and of the

supplied application circuit.

6.2

Battery voltage sense

To detect undervoltage conditions at the battery a sense comparator block is available

within the TLE 6389. The voltage at the SI input is compared to an internal reference of

typ. 1.25V. The output of the comparator drives a NMOS structure giving a low signal at

SO as soon as the voltage at SI decreases below this threshold. In the 5V fixed version

an internal pull up resistor is connected from the drain of the NMOS to the output of the

buck converter, in the variable version SO is open drain.

The sense in voltage divider can be switched to high impedance by a low signal at the

SI_ENABLE to avoid high current consumption to GND (TLE6389-2 GV50 and

TLE6389-3 GV50 only).

Of course the sense comparator can be used for any input voltage and does not have to

be used for the battery voltage sense only.

6.3

Undervoltage Reset

The output voltage is monitored continuously by the internal undervoltage reset

comparator. As soon as the output voltage decreases below the thresholds given in the

characteristics the NPN structure pulls RO low (latched). In the 5V fixed version an

internal pull up resistor is connected from the collector of the NPN to the output of the

buck converter, in the variable version RO is open collector.

At power up RO is kept low until the output voltage has reached its reset threshold and

stayed above this threshold for the power on reset delay time.

TLE6389 Datasheet(PDF) 26 Page - Infineon Technologies AG