ALTAIR05T-800TR STMicroelectronics, ALTAIR05T-800TR Datasheet - Page 14

• Manufacturer Part Number: ALTAIR05T-800TR
• Description: Switching Converters, Regulators & Controllers 800V Off-line QR Switching Regulator
• Manufacturer: STMicroelectronics

Specifications of ALTAIR05T-800TR

• Input Voltage: 11.5 V to 23 V
• Switching Frequency: 166 KHz
• Operating Temperature Range: - 55 C to + 150 C
• Mounting Style: SMD/SMT
• Package / Case: SOIC-16
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Application information
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The voltage on the pin is both top and bottom limited by a double clamp, as illustrated in the
internal diagram of the ZCD block of
the lower clamp is at -60 mV. The interface between the pin and the auxiliary winding is a
resistor divider. Its resistance ratio as well as the individual resistance values has to be
properly chosen (see
feedforward
Please note that the maximum I
(AMR) in all the Vin range conditions (85-265 Vac). No capacitor is allowed between ZCD
pin and the auxiliary transformer.
The switching frequency is top-limited below 166 kHz, as the converter’s operating
frequency tends to increase excessively at light load and high input voltage.
A Starter block is also used to start-up the system, that is, to turn on the MOSFET during
converter power-up, when no or a too small signal is available on the ZCD pin.
The starter frequency is 2 kHz if COMP pin is below burst mode threshold, i.e. 1 V, while it
becomes 8 kHz if this voltage exceed this value.
After the first few cycles initiated by the starter, as the voltage developed across the auxiliary
winding becomes large enough to arm the ZCD circuit, MOSFET’s turn-on starts to be
locked to transformer demagnetization, hence setting up QR operation.
The starter is activated also when the IC is in CC regulation and the output voltage is not
high enough to allow the ZCD triggering.
If the demagnetization completes – hence a negative-going edge appears on the ZCD pin –
after a time exceeding time T
again, with some delay to ensure minimum voltage at turn-on. If, instead, the negative-going
edge appears before T
edge after T
skipped (“valley-skipping mode”,
exceeding 1/T
Figure 12. Drain ringing cycle skipping as the load is progressively reduced
Note that when the system operates in valley skipping-mode, uneven switching cycles may
be observed under some line/load conditions, due to the fact that the OFF-time of the
MOSFET is allowed to change with discrete steps of one ringing cycle, while the OFF-time
needed for cycle-by-cycle energy balance may fall in between. Thus one or more longer
switching cycles is compensated by one or more shorter cycles and vice versa. However,
this mechanism is absolutely normal and there is no appreciable effect on the performance
of the converter or on its output voltage.
V
DS
T
ON
BLANK
block”).
T
T
osc
FW
BLANK
T
(limit condition)
V
P
turns-on the MOSFET. In this way one or more drain ringing cycles is
in
.
= P
“Section 5.4: Constant voltage
in'
BLANK
BLANK
has elapsed, it is ignored and only the first negative-going
Doc ID 17957 Rev 1
ZCD/FB
Figure
t
from the previous turn-on, the MOSFET is turned on
Figure
V
DS
sunk/sourced current has to not exceed ±2 mA
12) and the switching frequency is prevented from
T
11. The upper clamp is typically at 3.3 V, while
osc
P
in
= P
in''
operation” and
< P
in'
t
“Section 5.6: Voltage
V
DS
T
ALTAIR05T-800
osc
P
in
= P
in'''
< P
in''