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參數(shù)資料
| 型號： | L6599TR |
| 廠商： | STMICROELECTRONICS |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | 0.8 A SWITCHING CONTROLLER, 500 kHz SWITCHING FREQ-MAX, PDSO16 |
| 封裝： | LEAD FREE, SOP-16 |
| 文件頁數(shù)： | 17/36頁 |
| 文件大小： | 633K |
| 代理商： | L6599TR |
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Application information
L6599
24/36
Figure 30. Lossless current sensing technique, with capacitive shunt
The device is equipped with a current sensing input (pin 6, ISEN) and a sophisticated
overcurrent management system. The ISEN pin is internally connected to the input of a first
comparator, referenced to 0.8V, and to that of a second comparator referenced to 1.5V. If the
the first comparator is tripped and this causes an internal switch to be turned on and
increase the oscillator frequency and thereby limit energy transfer. The discharge will go on
until the voltage on the ISEN pin has dropped by 50mV; this, with an averaging time in the
range of 10/fmin, ensures an effective frequency rise. Under output short circuit, this
operation results in a nearly constant peak primary current.
It is normal that the voltage on the ISEN pin may overshoot above 0.8V; however, if the
voltage on the ISEN pin reaches 1.5V, the second comparator will be triggered, the L6599
will shutdown and latch off with both the gate-drive outputs and the PFC_STOP pin low,
hence turning off the entire unit. The supply voltage of the IC must be pulled below the
UVLO threshold and then again above the start-up level in order to restart. Such an event
may occur if the soft-start capacitor CSS is too large, so that its discharge is not fast enough
or in case of transformer's magnetizing inductance saturation or a shorted secondary
rectifier.
low-side MOSFET is used, note the particular connection of the resonant capacitor. In this
way the voltage across RS is related to the current flowing through the high-side MOSFET
and is positive most of the switching period, except for the time needed for the resonant
current to reverse after the low-side MOSFET has been switched OFF. Assuming that the
time constant of the RC filter is at least ten times the minimum switching frequency fmin, the
approximate value of RS can be found using the empirical equation:
where ICrpkx is the maximum desired peak current flowing through the resonant capacitor
and the primary winding of the transformer, which is related to the maximum load and the
minimum input voltage.
pk
L6599
6
ISEN
Cr
RA
RB
1N4148
CB
CA
1N4148
τ ≈
10
fmin
VCrpk
ICr
R
S
Vs
pkx
I
Crpkx
---------------
50.8
I
Crpkx
------------------
4
I
Crpkx
---------------
≈≈
=
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