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參數(shù)資料
| 型號： | 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 |
| 文件頁數(shù)： | 6/23頁 |
| 文件大?。?/td> | 720K |
| 代理商： | L6668TR |
L6668
14/23
At converter power-down the system will lose regulation as soon as the input voltage is so low that either
peak current or maximum duty cycle limitation is tripped. Vcc will then drop and stop IC activity as it falls
below the UVLO threshold (8.7V typ.).
The Vcc_OK signal is de-asserted as the Vcc voltage goes below a threshold Vccrestart located at about
5V. The HV generator can now restart but, if Vin < Vinstart, as shown in figure 36, HV_EN is de-asserted
too and the HV generator is disabled.
This prevents converter's re-start attempts and ensures monotonic output voltage decay at power-down.
The low restart threshold Vccrestart ensures that, during short circuits, the restart attempts of the L6668 will
have a very low repetition rate, as shown in the timing diagram of figure 37, and that the converter will
work safely with extremely low power throughput.
4.2 Frequency Foldback Block and operation at medium/light load
At heavy load, namely as the voltage on pin COMP (VCOMP) is higher than 3V, the device works at a fixed
frequency like a standard current mode PWM controller.
As the load is reduced, and the VCOMP voltage falls below 3V (approximately corresponding to 50% of the
maximum load in a fully DCM system), the oscillator frequency can be made dependent on converter's
load conditions - the lower the load, the lower the frequency and vice versa.
Figure 38. Frequency foldback function: oscillator frequency is a function of COMP voltage
This is done by adding an external resistor RSTBY between pins RCT (#16) and STBY (#13), which acti-
vates the circuit shown in figure 38.
When VCOMP is below 3 V (oscillator's peak voltage) the voltage on the STBY pin, which is internally con-
nected to a current sink, tracks VCOMP and then some of the current that charges CT is diverted to ground
through the STBY pin.
In this way the rate of rise of the voltage across CT is slowed down and the oscillator frequency decreased,
the lower VCOMP the lower the frequency. Instead, when VCOMP is greater than 3 V the STBY pin features
high impedance and the oscillator frequency fosc will be determined by RT and CT. These components can
be then calculated as it is usually done with this type of oscillator:
VCOMP
fosc
1.4
3.0
4.4
RSTBY
3.0V
-
+
RSTBY
L6668
CT
RT
Vref
13
16
8
STBY
COMP
RCT
OSCILLATOR
VCOMP
fosc
1.4
3.0
4.4
RSTBY
3.0V
-
+
RSTBY
L6668
CT
RT
Vref
13
16
8
STBY
COMP
RCT
OSCILLATOR
R
T CT
1.4
f
os c
---------
=
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| L667 | 制造商:BURNDY 功能描述:L-DIE |
| L-667 | 制造商:RHOMBUS-IND 制造商全稱:Rhombus Industries Inc. 功能描述:Common Mode Inductor For DC/DC Power supply |
| L-668 | 制造商:RHOMBUS-IND 制造商全稱:Rhombus Industries Inc. 功能描述:Common Mode Inductor For DC/DC Power supply |
| L-669 | 制造商:RHOMBUS-IND 制造商全稱:Rhombus Industries Inc. 功能描述:Common Mode Inductor For DC/DC Power supply |
| L6690 | 制造商:HAMAMATSU 制造商全稱:Hamamatsu Corporation 功能描述:INFRARED PULSED LASER DIODE |
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