l6611 STMicroelectronics, l6611 Datasheet - Page 22

• Manufacturer Part Number: l6611
• Description: Digitally Programmable Secondary Housekeeping Controller
• Manufacturer: STMicroelectronics

L6611
– Dmon input undervoltage: when an undervoltage on Dmon is detected, MFAULT is put high, Cout is
Figure 20. Fault timing diagram
5
The device monitors the primary bulk voltage and warns the system when the power is about to be lost pulling
down the PW_OK output.
The ACsns pin is typically connected to one of the windings of the main transformer (see fig. 21). Through a
single-diode rectification filter, a voltage equal to V
pacitor on primary side and N is the transformer turn ratio) is present at point B. A resistor (R
to clamp voltage spikes present.
The fault signal is generated by means of AC_GOOD, the output of an internal comparator; this comparator is
internally referred to a trimmable 2.5V reference and indicates an AC fault if the voltage applied at its externally
available (non-inverting) input is below the internal reference, as shown in fig. 21.
This comparator is provided with current hysteresis instead of a more usual voltage hysteresis: an internal 50µA
current generator is ON if the voltage is below 2.5V and is turned off when the voltage applied at the non-invert-
ing input exceeds 2.5V.
This approach provides an additional degree of freedom: it is possible to set the ON threshold and the OFF
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DFAULT; in the "Application ideas" section, another simple circuit is showed to guarantee the same pro-
tection without the SCR.
pulled low (an internal OCP_BOUNCE signal is generated, see fig. 19) and PW_OK falls down. This
function is enabled 64ms after the UVLO signal falls down. Debounce logic is implemented so that
MFAULT and OCP_BOUNCE signals are generated only if the undervoltage condition lasts more than
500µs.
The Dmon UV and OV protections can be set to work with thresholds set for 5V or 3.3V output voltage:
the choice depends on the IC programming.
AC SENSE (MAINS UNDERVOLTAGE WARNING)
(*) Dmon is connected to the Auxiliary output Rail
Auxiliary output’s overvoltage
Dmon
Dfault current
Mfault
POK
(*)
Output
Mfault
POK
Main output’s overvoltage
Dmon
Cout
Mfault
POK
B
(*)
= V
BULK
Auxiliary output’s undervoltage
/N (where V
Output
Mfault
POK
Main output’s undervoltage
BULK
is the voltage across the bulk ca-
F
) could be useful