L6610D STMicroelectronics, L6610D Datasheet - Page 23

• Manufacturer Part Number: L6610D
• Description: IC CTRLR HOUSEKEEPING BCD 24SOIC
• Manufacturer: STMicroelectronics

Specifications of L6610D

• Applications: Programmable Housekeeping Controller
• Voltage - Supply: 4.2 V ~ 7 V
• Current - Supply: 5mA
• Operating Temperature: 0°C ~ 105°C
• Mounting Type: Surface Mount
• Package / Case: 24-SOIC (7.5mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Input: -

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. 23). 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. 23.
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
threshold separately by properly choosing the resistors of the external divider. The following relationships can
be established for the ON (VB
which, solved for R1 and R2, yields:
Both the ACsns threshold and the hysteresis current can be trimmed (see "On board trimming and mode oper-
ating" section).
Figure 23. ACsns circuit and timing diagram
6
In applications like desktop PC's, server or web server, the system usually consists of two converters (Main and
Auxiliary) that can be supplied directly from either the AC Mains or a PFC stage. The control and supervision at
the secondary side is usually entrusted to a housekeeping circuit.
The Auxiliary section supplies a stand-by voltage (5V typ.) through a flyback converter. The Main section, in
forward configuration, presents 5 standard outputs (3.3V, ±5V, ±12V).
At the secondary side, the housekeeping circuitry governed by the L6610 checks the outputs and sends control
signals to the primary side through three optocouplers. It also generates power good information to the system
while managing all timings during power-up and power-down sequences. In fig. 24 a detailed circuit for the sec-
ondary side is presented; it is possible to note the very low number of external components required.
AC_GOOD
L6610
AC SENSE (MAINS UNDERVOLTAGE WARNING)
APPLICATION EXAMPLE
I
HYS=50 A
R
VB
--------------------------------- -
+
_
1
GND
+2.5V
=
O N
R
VB
------------------------------------------------ -
1
(ON)
–
O N
ACsns
2.5
) and OFF (VB
50 A
–
B
=
VB
2.5
------- -
R
R
R
2
O FF
1
2
+
R
50 A
F
(OFF)
C
B
1
= V
) thresholds of the input voltage:
BULK
/N (where V
VB
R
2
PW_OK
V
VB
AC_GOOD
O FF
=
ACsns
R
1
BULK
--------------------
R
------------------------------------ -
VB
1
R
+
2
is the voltage across the bulk ca-
R
O FF
2.5
2
VB(on)
=
–
2.5
2.5
=50 A*R
ON
F
) could be useful
1
VB(off)
L6610
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