ALTAIR05T-800 STMicroelectronics, ALTAIR05T-800 Datasheet - Page 20

• Manufacturer Part Number: ALTAIR05T-800
• Description: IC PRIMARY SWITCHING REG 16NSOIC
• Manufacturer: STMicroelectronics

Specifications of ALTAIR05T-800

• Output Isolation: Isolated
• Voltage - Input: 11.5 ~ 23 V
• Voltage - Output: 800V
• Power (watts): 900mW
• Operating Temperature: -25°C ~ 125°C
• Package / Case: 16-SOIC (0.154", 3.90mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Application information
5.8
5.9
20/28
Burst-mode operation at no load or very light load
When the voltage at the COMP pin falls 65 mV below a threshold fixed internally at a value,
V
reduced at a lower value to minimize Vcc capacitor discharge.
In this condition the converter operates in burst-mode (one pulse train every T
µs), with minimum energy transfer.
As a result of the energy delivery stop, the output voltage decreases: after 500 µs the
controller switches-on the MOSFET again and the sampled voltage on the ZCD pin is
compared with the internal reference. If the voltage on the EA output, as a result of the
comparison, exceeds the V
OFF for another 500 µs period.
In this way the converter works in burst-mode with a nearly constant peak current defined by
the internal disable level. Then a load decrease causes a frequency reduction, which can go
down even to few hundred hertz, thus minimizing all frequency-related losses and making it
easier to comply with energy saving regulations. This kind of operation, shown in the timing
diagrams of
peak current is low
Figure 18. Load-dependent operating modes: timing diagrams
Soft-start and starter block
The soft start feature is automatically implemented by the constant current block, as the
primary peak current is limited from the voltage on the C
During start-up, as the output voltage is zero, the IC starts in CC mode with no high peak
current operations. In this way the voltage on the output capacitor increases slowly and the
soft-start feature is ensured.
Actually the C
on others circuit parameters, like transformer ratio, sense resistor, output capacitors and
load. The user can define the best appropriate value by experiments.
COMPBM
COMP
V
COMPL
I
DS
, the IC is disabled with the MOSFET kept in OFF state and its consumption
Figure 18
REF
Normal-mode
value is not important to define the soft-start time, as its duration depends
along with the others previously described, is noise-free since the
COMPL
Doc ID 17957 Rev 1
T
START
threshold, the device restarts switching, otherwise it stays
T
START
Burst-mode
T
START
REF
capacitor.
T
START
Normal-mode
ALTAIR05T-800
START
hyster.
65 mV
=500