TLE6389_07 Datasheet, PDF (26/38 Pages) Infineon Technologies AG – Step-Down DC/DC Controller

TLE 6389
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.
Datasheet Rev. 2.1
26
2007-08-13