
TLE 6387 G
Target Datasheet Rev. 0.5
14
2001-08-27
results from its inevitable series resistance and the average load current
. In
order not to spoil the current mode signal this offset is slowly compensated using the
inherent inertia of the voltage loop. Please note, since the inputs of OTA
EA and OCACM
are internally connected, it is not possible to increase the output voltage by feeding back
only a fraction of the output voltage to pin 9 (FB). In fact , whenever the generated output
voltage differs from the voltage sensed at pin 9 (FB), a large DC offset is added to the
internal current mode signal, which cannot be compensated by OTA
CC and which
consequently will result in a clampled output voltage.
Protection Circuitry (only avaiable at version GV50)
To achieve a safe operation of the controller and its load connected, TLE 6387 G is
equipped with different protection circuitry. To warn loads supplied of temporary
undervoltages or overvoltages the output voltage is continuously supervised for
undervoltages or overvoltages. To prevent the undervoltage and overvoltage
comparators C
uv
and C
ov
from being triggered due to inevitable noise that is
superimposed on the voltage sensed at pin 9 (FB), both comparators are equipped with
a corresponding hysteresis as well as an input low pass filter. In case an undervoltage
or overvoltage has been detected, the reset signals at pin 6 (RST) and pin 7 (RST) are
set according to1. If the undervoltage or overvoltage has passed both signals are reset
after 21 ms. A corresponding timing diagram is given in 1 and 2.
In order to make sure the output voltage supervisor is working properly down to an output
voltage of 1 V regardless of the supply voltage at pin 2 (
V
S), its supply voltage is switched
between the internal voltage supply and the converters output voltage if necessary (cf.
“Internal Power Supply”).
To protect the converter and the driven power switch from destruction due to a short-
circuited output, the voltage drop across the power switch is checked cycle-by-cycle. If
this voltage drop exceeds 1.25 V, the driver is immediately shut off for the remaining part
of the respective cycle. As a result, the duty cycle is kept constant at a value as small as
possible.
In order to prevent the output voltage from high overvoltages, which may be caused by
a missing output capacitor or a broken connection between pin 9 (FB) and the output
capacitor, TLE 6387 G is equipped with a smart wirebreak protection, which shortly
checks the status of pin 9 (FB) whenever the controller is turned on.
V
FB
RST RST
Undervoltage
Z
L
Overvoltage
Z
L
Else
L
Z
Table 1 Reset Logic Truth Table
I
L
R
L
()