STR-F6600 Просмотр технического описания (PDF) - Allegro MicroSystems
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STR-F6600 Datasheet PDF : 16 Pages
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Series STR-F6600
OFF-LINE
QUASI-RESONANT FLYBACK
SWITCHING REGULATORS
Functional Description and Operation
The voltage on the VIN terminal (pin 4) controls startup
and shutdown of the Series STR-F6600 devices.
Figure 1 shows a typical start up circuit. The VIN
terminal voltage during startup is shown in figure 2.
At startup, C2 is charged through the startup resistor RS.
When the VIN terminal voltage reaches 16 V (typ.), the
control circuit enables regulator operation. Once the
regulator starts, it draws up to 30 mA from C2 causing the
voltage on C2 to fall momentarily. Once the regulator
output voltage is established, the drive winding D starts to
charge C2 via D2. The voltage on C2 thus recovers to the
nominal drive voltage (18 V).
As shown in figure 3, the input current is below 100 µA
(at TM = 25°C) prior to control circuit turn on. The latch
circuit holding current is 400 µA (max.). To ensure latch
operation, the current in RS at the lowest ac input voltage
should be at least 500 µA.
IIN
30 mA
(MAX.)
IIN(ON)
Figure 1 – Start-Up Circuit
VIN
16 V ON-STATE VOLTAGE (VINT)
(TYP.)
11 V
(MAX.)
UNDER-VOLTAGE LOCKOUT (VINQ)
DRIVE WINDING
VOLTAGE
STARTUP
DELAY
TIME
Figure 2 – Waveform of VIN Terminal Voltage
at Startup
100 µA
(MAX.)
IIN(OFF)
11 V
(MAX.)
14.4 V VIN
(MIN.)
Figure 3 – Supply Terminal Current, IIN
The value of RS thus determines the charge time of C2
and thus the startup delay. RS is typicaly 68 kΩ for wide
operation (90 V ac to 265 V ac) and 100 kΩ for 220 volt
ac operation.
The choice of C2 is a compromise between an accept-
able startup delay (in conjunction with RS) and a hold-up
time sufficient to keep pin 4 above its under-voltage
shutdown threshold of 11 V. Typically C2 is in the range
of 47 µF to 100 µF.
continued, next page...
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