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ALTAIR05T-800TR
Off-line all-primary-sensing switching regulator
October 2010 Doc ID 17957 Rev 1 1/28
TAIR05T -800Off-line all-primary-sensing switching regulator
Features Constant voltage and constant current output
regulation (CV/CC) with no optocoupler Tight regulation also in presence of heavy load
transients 800 V avalanche rugged internal power section Quasi-resonant (QR) operation Low standby power consumption Automatic self-supply Input voltage feedforward for mains-
independent cc regulation Output cable drop compensation SO16 package
Applications AC-DC chargers for mobile phones and other
hand-held equipments Compact SMPS that requires a precise current
and/or voltage regulation
DescriptionALTAIR05T -800 is a high-voltage all-primary
sensing switcher intended for operating directly
from the rectified mains with minimum external
parts. It combines a high-performance low-
voltage PWM controller chip and an 800 V
avalanche-rugged power section in the same
package.
Figure 1. Block diagram
Contents ALTAIR05T-8002/28 Doc ID 17957 Rev 1
Contents Device 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 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
5.6 Voltage feedforward block . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
5.7 Cable drop compensation (CDC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
5.8 Burst-mode operation at no load or very light load . . . . . . . . . . . . . . . . . . 20
5.9 Soft-start and starter block . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
5.10 Hiccup mode OCP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
5.11 Layout recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Typical application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Order codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
ALTAIR05T-800 Device description
Doc ID 17957 Rev 1 3/28
1 Device description
The device combines two silicon in the same package: a low voltage PWM controller and
an 800 V avalanche rugged power section.
The controller chip is a current-mode specifically designed for offline quasi-resonant flyback
converters.
The device features a unique characteristic: it is capable of providing constant output
voltage (CV) and constant output current (CC) regulation using primary-sensing feedback.
This eliminates the need for the optocoupler, the secondary voltage reference, as well as the
current sensor, still maintaining quite accurate regulation also in presence of heavy load
transients. Additionally, it is possible to compensate the voltage drop on the output cable, so
as to improve CV regulation on the external accessible terminals.
Quasi-resonant operation is guaranted by means of a transformer demagnetization sensing
input that turns on the power section. The same input serves also the output voltage
monitor, to perform CV regulation, and the input voltage monitor, to achieve mains-
independent CC regulation (line voltage feedforward).
The maximum switching frequency is top-limited below 166 kHz, so that at medium-light
load a special function automatically lowers the operating frequency still maintaining the
valley switching operation. At very light load, the device enters a controlled burst-mode
operation that, along with the built-in high-voltage start-up circuit and the low operating
current, helps minimize the standby power.
Although an auxiliary winding is required in the transformer to correctly perform CV/CC
regulation, the chip is able to power itself directly from the rectified mains. This is useful
especially 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 stringent energy-saving recommendations, then the device needs to
be powered via the auxiliary winding.
In addition to these functions that optimize power handling under different operating
conditions, the device offers protection features that considerably increase end-product’s
safety and reliability: auxiliary winding disconnection - or brownout – detection and shorted
secondary rectifier - or transformer’s saturation – detection. All of them are auto restart
mode.
Pin connection ALTAIR05T-800
4/28 Doc ID 17957 Rev 1
2 Pin connection
Figure 2. Pin connection (top view)
Note: The copper area for heat dissipation has to be designed under the drain pins
Table 1. Pin functions
ALTAIR05T-800 Pin connection
Doc ID 17957 Rev 1 5/28
Table 1. Pin functions (continued)
Maximum ratings ALTAIR05T-800
6/28 Doc ID 17957 Rev 1
3 Maximum ratings
3.1 Absolute maximum ratings
3.2 Thermal data
Table 2. Absolute maximum ratings
Table 3. Thermal data
ALTAIR05T-800 Electrical characteristics
Doc ID 17957 Rev 1 7/28
4 Electrical characteristics
(TJ = -25 to 125 °C, Vcc = 14 V; unless otherwise specified)
Table 4. Electrical characteristics
Electrical characteristics ALTAIR05T-800
8/28 Doc ID 17957 Rev 1 Parameters tracking each other
Table 4. Electrical characteristics (continued)
ALTAIR05T-800 Electrical characteristics
Doc ID 17957 Rev 1 9/28
Figure 3. COSS output capacitance variation
Figure 4. Off state drain and source current test circuit
Note: The measured I DSS is the sum between the current across the start-up resistor and the
effective MOSFET’s off state drain current.
Figure 5. Start-up current test circuit
Electrical characteristics ALTAIR05T-800
10/28 Doc ID 17957 Rev 1
Figure 6. Quiescent current test circuit
Figure 7. Operating supply current test circuit
Note: The circuit across the ZCD pin is used for switch-on synchronization
Figure 8. Quiescent current during fault test circuit
ALTAIR05T-800 Application information
Doc ID 17957 Rev 1 11/28
5 Application information
The device is an off-line all-primary sensing switching regulator, based on quasi-resonant
flyback topology.
Depending on converter’s load condition, the device is able to work in different modes (see
Figure9): QR mode at heavy load. Quasi-resonant operation lies in synchronizing MOSFET's
turn-on to the transformer’s demagnetization by detecting the resulting negative-going
edge of the voltage across any winding of the transformer. Then the system works
close to the boundary between discontinuous (DCM) and continuous conduction
(CCM) of the transformer. As a result, the switching frequency is different for different
line/load conditions (see the hyperbolic-like portion of the curves in Figure 9). Minimum
turn-on losses, low EMI emission and safe behavior in short circuit are the main
benefits of this kind of operation.
2. Valley-skipping mode at medium/ light load. Depending on voltage on COMP pin, the
device defines the maximum operating frequency of the converter. As the load is
reduced MOSFET’s turn-on does not occur any more on the first valley but on the
second one, the third one and so on. In this way the switching frequency is no longer
increased (piecewise linear portion in Figure 9).
3. Burst-mode with no or very light load. When the load is extremely light or disconnected,
the converter enters a controlled on/off operation with constant peak current.
Decreasing the load result in 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 or recommendations. Being the peak current
very low, no issue of audible noise arises.
Figure 9. Multi-mode operation of ALTAIR05T-800
Application information ALTAIR05T-800
12/28 Doc ID 17957 Rev 1
5.1 Power section and gate driver
The power section guarantees safe avalanche operation within the specified energy rating
as well as high dv/dt capability. The Power MOSFET has a V(BR)DSS of 800 V min. and a
typical RDS(on) of 11 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 power MOSFET cannot be turned on
accidentally.
5.2 High-voltage start-up 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 of Figure 10, when power is applied to the circuit and
the voltage on the input bulk capacitor is high enough, the HV generator is sufficiently
biased to start operating, thus it draws about 5.5 mA (typical) from the bulk capacitor. Most
of this current charges the bypass capacitor connected between the Vcc pin and ground and
make its voltage rise linearly.
As the Vcc voltage reaches the start-up threshold (13 V typ.) the chip starts operating, the
internal power MOSFET is enabled to switch and the HV generator is cut off. The IC is
powered by the energy stored in the Vcc capacitor.
The chip is able to power itself directly from the rectified mains: when the voltage on the VCC
pin falls below Vccrestart (10.5V typ.), during each MOSFET’s off-time the HV current
generator is turned on and charges the supply capacitor until it reaches the VCCOn
threshold.
In this way, the self-supply circuit develops a voltage high enough to sustain the operation of
the device. This feature is useful especially during CC regulation, when the flyback voltage
generated by the auxiliary winding alone may not be able to keep Vcc above VCCrestart.
At converter power-down the system loses regulation as soon as the input voltage falls
below VStart. This prevents converter’s restart attempts and ensures monotonic output
voltage decay at system power-down.
ALTAIR05T-800 Application information
Doc ID 17957 Rev 1 13/28
Figure 10. Timing diagram: normal power-up and power-down sequences
5.3 Zero current detection and triggering block
The zero current detection (ZCD) and triggering blocks switch on the power MOSFET if a
negative-going edge falling below 50 mV is applied to the ZCD/FB pin. To do so, the
triggering block must be previously armed by a positive-going edge exceeding 100 mV.
This feature is used to detect transformer demagnetization for QR operation, where the
signal for the ZCD input is obtained from the transformer’s auxiliary winding used also to
supply the IC.
Figure 11. ZCD block, triggering block
The triggering block is blanked after MOSFET’s turn-off to prevent any negative-going edge
that follows leakage inductance demagnetization from triggering the ZCD circuit
erroneously.
This blanking time is dependent on the voltage on COMP pin: it is TBLANK = 30 µs for VCOMP
= 0.9 V, and decreases almost linearly down to TBLANK = 6 µs for VCOMP = 1.3 V
Application information ALTAIR05T-800
14/28 Doc ID 17957 Rev 1
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 Figure 11. The upper clamp is typically at 3.3 V, while
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 “Section 5.4: Constant voltage operation” and “Section 5.6: Voltage
feedforward block”).
Please note that the maximum IZCD/FB sunk/sourced current has to not exceed ±2 mA
(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 TBLANK from the previous turn-on, the MOSFET is turned on
again, with some delay to ensure minimum voltage at turn-on. If, instead, the negative-going
edge appears before TBLANK has elapsed, it is ignored and only the first negative-going
edge after TBLANK turns-on the MOSFET. In this way one or more drain ringing cycles is
skipped (“valley-skipping mode”, Figure 12) and the switching frequency is prevented from
exceeding 1/TBLANK.
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.
