參數(shù)資料
型號(hào): L6668TR
廠商: STMICROELECTRONICS
元件分類: 穩(wěn)壓器
英文描述: 0.8 A SWITCHING CONTROLLER, 105 kHz SWITCHING FREQ-MAX, PDSO16
封裝: LEAD FREE, SOP-16
文件頁(yè)數(shù): 5/23頁(yè)
文件大?。?/td> 720K
代理商: L6668TR
13/23
L6668
With reference to the timing diagram of figure 36, when power is first applied to the converter the voltage
on the bulk capacitor (Vin) builds up and, as it reaches about 80V, the HV generator is enabled to oper-
ate (HV_EN is pulled high) so that it draws about 1 mA. This current, diminished by the IC consumption,
charges the bypass capacitor connected between pin Vcc (5) and ground and makes its voltage rise al-
most linearly.
Figure 36. Timing diagram: normal power-up and power-down sequences
As the Vcc voltage reaches the start-up threshold (13.5V typ.) the low-voltage chip starts operating 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 until the self-supply circuit (typically an auxiliary winding of the transformer and a
steering diode) develops a voltage high enough to sustain the operation.
The residual consumption of this circuit is just the one on the 15M
resistor (10 mW at 400 Vdc), typically
50-70 times lower, under the same conditions, as compared to a standard start-up circuit made with an
external dropping resistor.
Figure 37. Timing diagram showing short-circuit behavior
Vcc
OUT
HV_EN
Vcc ON
Vcc OFF
Vcc restart
t
Vin
V
HVstart
IHV
1 mA
t
Vcc_OK
Power-up
Power-down
Normal
operation
regulation is lost here
Vcc
OUT
HV_EN
Vcc ON
Vcc OFF
Vcc restart
t
Vin
V
HVstart
IHV
1 mA
t
Vcc_OK
Power-up
Power-down
Normal
operation
regulation is lost here
Vcc
OUT
Vcc_OK
VccON
VccOFF
Vccrest
IHV
1 mA
Short circuit occurs here
t
Vcc
OUT
Vcc_OK
VccON
VccOFF
Vccrest
IHV
1 mA
Short circuit occurs here
t
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