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ALTAIR04-900TR
Off-line all-primary-sensing switching regulator
October 2014 DocID18211 Rev 3 1/29
ALTAIR04-900Off-line all-primary-sensing switching regulator
Datasheet - production data
Features Optoless primary side constant voltage
operations Adjustable and mains-independent maximum
output current for safe operations during
overload/short-circuit conditions 900 V avalanche-rugged internal power section Quasi-resonant valley switching operation Low standby consumption Overcurrent protection against transformer
saturation and secondary diode short-circuit SO16N package
Applications SMPS for energy metering Auxiliary power supplies for 3-phase input
industrial systems AC-DC adapters
DescriptionThe ALTAIR04-900 is a high voltage all-primary-
sensing switcher, operating directly from the
rectified mains with minimum external parts. It
combines a high-performance low voltage PWM
controller chip and a 900 V avalanche-rugged
power section in the same package.
Figure 1. Block diagram
Contents ALTAIR04-9002/29 DocID18211 Rev 3
Contents Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Pin connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63.1 Absolute maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.2 Thermal data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Application information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115.1 Power section and gate driver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
5.2 High voltage start-up generator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
5.3 Zero-current detection and triggering block . . . . . . . . . . . . . . . . . . . . . . . 13
5.4 Constant voltage operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
5.5 Constant current operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
5.6 Voltage feed-forward block . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
5.7 Burst-mode operation (no load or very light load) . . . . . . . . . . . . . . . . . . 18
5.8 Soft-start and starter block . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
5.9 Hiccup-mode OCP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
5.10 Layout recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Typical applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 226.1 Test board: evaluation data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
6.2 Test board: main waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Ordering information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
DocID18211 Rev 3 3/29
ALTAIR04-900 Description
1 Description
This device combines two silicons in the same package: a low voltage PWM controller and a
900 V avalanche-rugged power section.
The controller is in current-mode specifically designed for off-line quasi-resonant flyback
converters.
The device provides a constant output voltage using the primary-sensing feedback. This
eliminates the need for the optocoupler, the secondary voltage reference, as well as the
current sensor, still maintaining an accurate regulation. Besides, the maximum deliverable
output current can be set so to increase the end-product safety and reliability during fault
events.
Quasi-resonant operation is guaranteed by a transformer demagnetization sensing input
which turns on the power section. The same input also serves the output voltage monitoring,
to perform CV regulation, and to achieve mains-independent maximum deliverable output
current (line voltage feed-forward).
The maximum switching frequency is top-limited 166 kHz, so that at light-to-medium load a
special function automatically lowers the operating frequency still maintaining the valley
switching operation. When the load is very light, the device enters a controlled burst-mode
operation that, along with the built-in high voltage start-up circuit and the low operating
current, minimizes the standby power.
Although an auxiliary winding is required in the transformer to correctly perform CV/CC
regulation, the chip powers itself directly from the rectified mains. This is important during
CC regulation, where the flyback voltage, generated by the winding, drops below UVLO
threshold.
However, if ultra low no-load input consumption is required to comply with the most strict
energy-saving recommendations, then the device needs to be powered by the auxiliary
winding.
These functions optimize power handling under different operating conditions. The device
offers protection features that, in auto restart-mode, increase end-product safety and
reliability: Auxiliary winding disconnection, or brownout Detection Shorted secondary rectifier, or transformer saturation
Pin connection ALTAIR04-900
4/29 DocID18211 Rev 3
2 Pin connection
Figure 2. Pin connection (top view)
Note: The copper area has to be placed under the drain pins to dissipate heat.
Table 1. Pin functions
DocID18211 Rev 3 5/29
ALTAIR04-900 Pin connection
Table 1. Pin functions (continued)
Maximum ratings ALTAIR04-900
6/29 DocID18211 Rev 3
3 Maximum ratings
3.1 Absolute maximum ratings
3.2 Thermal data
Table 2. Absolute maximum ratings
Table 3. Thermal data
DocID18211 Rev 3 7/29
ALTAIR04-900 Electrical characteristics
4 Electrical characteristics
(TJ = -40 to 125 °C, Vcc = 14 V; unless otherwise specified)
Table 4. Electrical characteristics
Electrical characteristics ALTAIR04-900
8/29 DocID18211 Rev 3 Parameters track one to each other
Table 4. Electrical characteristics (continued)
DocID18211 Rev 3 9/29
ALTAIR04-900 Electrical characteristics
Note: The measured I DSS is the sum between the current across the start-up resistor and the
MOSFET off-state drain current.
Electrical characteristics ALTAIR04-900
10/29 DocID18211 Rev 3
Note: The circuit across the ZCD pin is used for the switch-on synchronization.
11/29ALTAIR04-900 Application information
5 Application information
Application information ALTAIR04-900
12/29 DocID18211 Rev 3
5.1 Power section and gate driver
The power section guarantees the safe avalanche operation within the specified energy
rating as well as high dv/dt capability. The MOSFET has a V(BR)DSS of 900 V min. and a
typical RDS(on) of 16 Ω.
The gate driver is designed to supply a controlled gate current during both turn-on and turn-
off in order to minimize common-mode EMI. Under UVLO conditions, an internal pull-down
circuit holds the gate low in order to ensure that the MOSFET cannot be turned on
accidentally.
5.2 High voltage start-up generator
Figure 10 shows the internal schematic of the high voltage start-up generator (HV
generator). The HV current generator is supplied through the DRAIN pin and it is enabled
only if the input bulk capacitor voltage is higher than VStart threshold, 50 VDC typically. When
the HV current generator is on, the Icharge current (5.5 mA typical value) is delivered to the
capacitor on the Vcc pin.
With reference to the timing diagram in Figure 10, when power is applied to the circuit and
the voltage on the input bulk capacitor is high, the HV generator is sufficiently biased to start
operating, thus it draws about 5.5 mA (typical) from the bulk capacitor. This current charges
the bypass capacitor connected between the Vcc pin and ground and rises its voltage
linearly.
As the Vcc voltage reaches the start-up threshold (13 V typ.) the chip starts operating, the
internal MOSFET is enabled to switch and the HV generator is cut off by the Vcc_OK signal
asserted high. The IC is powered by the energy stored in the Vcc capacitor.
The chip powers itself directly from the rectified mains: when the voltage on the Vcc pin falls
below Vccrestart (10.5V typ.), during each MOSFET off-time, the HV current generator turns
on and charges the supply capacitor until it reaches the VccOn threshold.
In this manner, the self-supply circuit develops a high voltage to sustain the operation of the
device. This feature is useful during CC regulation, when the flyback voltage generated by
the auxiliary winding alone, may not be able to keep Vcc above Vcc restart.
At converter power-down, the system loses regulation as soon as the input voltage falls
below VStart. This avoids converter restart attempts and assures monotonic output voltage
decay at system power-down.
DocID18211 Rev 3 13/29
ALTAIR04-900 Application information
5.3 Zero-current detection and triggering block
Application information ALTAIR04-900
14/29 DocID18211 Rev 3
divider. Its resistance ratio as well as the individual resistance values have to be properly
chosen (see “Section 5.4: Constant voltage operation” and “Section 5.6: Voltage feed-
forward block”).
The maximum IZCD/FB sunk/sourced current must not exceed ±2 mA (AMR) in all Vin range
conditions. No capacitor is allowed between ZCD pin and the auxiliary transformer.
The switching frequency is 166 kHz top-limited, as the converter operating frequency can
increase excessively at light load and on high input voltage.
A starter block is also used to start up the system, that is, to turn on the MOSFET during the
converter power-up, when any or a very small signal is available on ZCD pin.
The starter frequency is 2 kHz if COMP pin is below burst-mode threshold, 1 V, while it
becomes 8 kHz if this voltage exceeds this value.
After the first few cycles initiated by the starter, as the voltage developed across the auxiliary
winding arms the ZCD circuit, MOSFET turn-on starts to be locked to transformer
demagnetization, hence setting up QR operation.
The starter is also active when the IC is in CC regulation and the output voltage is not so
high to allow the ZCD triggering.
If the demagnetization completes, hence a negative-going edge appears on ZCD pin, after a
time exceeding TBLANK time, the MOSFET turns on again, with some delay to assure
minimum voltage at turn-on. If, instead, the negative-going edge appears before TBLANK has
elapsed, it is ignored and the first negative-going edge after TBLANK turns on the MOSFET.
Therefore one or more drain ringing cycles are skipped (“valley-skipping-mode”, Figure 12)
and the switching frequency cannot exceed 1/TBLANK.
Figure 12. Drain ringing cycle skipping as the load is progressively reduced
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
changes 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 are
compensated by one or more shorter cycles and vice versa. However, this mechanism is
absolutely normal and there is no appreciable impact on the performance of the converter or
on its output voltage.
DocID18211 Rev 3 15/29
ALTAIR04-900 Application information
5.4 Constant voltage operation
