TSM007 Просмотр технического описания (PDF) - STMicroelectronics
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TSM007 Datasheet PDF : 12 Pages
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TSM007
Functional Description
Soft start
A capacitor from the SS pin to GND provides the
soft start function. The capacitor starts to charge
when VIN reaches the UVLO threshold and Vref is
good.The soft start block enables the IC to start
with a progessive PWM duty cycle. The soft start
period is set by the external capacitor Css. The
soft start comparator drives the output driver low
when the SS pin voltage is greater than the CT pin
voltage minus one VF voltage..
CT
CT
Comp_osc
Cs_latch
RQ
VF
S !Q
Vref 1.4V_3.0V
SS
Iiss
Css
Iiss
10µA
Idss
4mA
Comp_SS
Out
2.4V VCT-VF
0.8V SS
Out
Out
Iiss=10µA
Tss = Soft start period
Brown out
A voltage proportionnal to the Bulk capacitor
voltage is applied to the BRNOUT pin. When this
pin signal is less than 2.5V, the IC is disabled: SS
and CT pins go low, Vref is disabled and the IC
goes to standby mode. All bias currents are
switched off. The 2.5V voltage at the negative
input of comparator Comp_Brown out is still
active. When Brown out voltage goes higher than
2.5V, Vref is enabled again. A startup period is
started, and then a soft start occurs..
filtered
Vin
R1
Ibr = 50µA
2.50V
Comp_brown out
Ibr Brown out
Vcc UVLO
R2
Vref
Vref_Status
Vref 1.4V_3.0V
Comp_osc
400µA
CT
CT
1mA
Startup Latch
S !Q
RQ
Out
Out
Brown out
2.5V Ibr=50µA
Tss = Cssx(Vthct-VF)/Iiss
Let’s assume Tss = 50ms
==> Css = TssxIiss/(Vthct-VF)
==> Css = 210nF
Let’s assume BRNOUT acts for Vfiltered = 200V
R2 = 15KΩ
R1 = R2(Vfiltered - UVLO) / UVLO
When BRNOUT is bellow 2.5V
IR2 = Vfiltered(R1+R2)
When BRNOUT is above 2.5V
IR2 = Ibr + Vfiltered(R1+R2)
BRNOUT = R2x(Ibr + Vfiltered(R1+R2))
R1 = 1185KΩ
R2 = 167µA
When BRNOUT is above 2.5V
IR2 = 237µA
BRNOUT = 3.55V
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