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FSBH0370_F116 View Datasheet(PDF) - Fairchild Semiconductor

Part Name
Description
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FSBH0370_F116
Fairchild
Fairchild Semiconductor Fairchild
FSBH0370_F116 Datasheet PDF : 16 Pages
First Prev 11 12 13 14 15 16
Brown-In Function of FSBH0F70A
The VIN pin functions are disabled in FSBH0F70A, but
FSBH0F70A has brown-in protection in the VDD pin.
There is a discharge current internal from VDD to ground
during startup. The HV source current must be larger
than IDD-ST to charge the capacitor of VDD. Therefore, the
brown-in level can be determined by RHV according to
the equation:
RHV
2VAC 12
IDDST
(4)
Green-Mode Operation
The FSBH-series uses feedback voltage (VFB) as an
indicator of the output load and modulates the PWM
frequency, as shown in Figure 30, such that the
switching frequency decreases as load decreases. In
heavy-load conditions, the switching frequency is
100kHz. Once VFB decreases below VFB-N (2.5V), the
PWM frequency starts to linearly decrease from 100kHz
to 18kHz to reduce switching losses. As VFB decreases
below VFB-G (2.0V), the switching frequency is fixed at
18kHz and the FSBH-series enters “deep” green mode to
reduce the standby power consumption.
Figure 30. PWM Frequency
As VFB decreases below VFB-ZDC (1.6V), the FSBH-
series enters burst-mode operation. When VFB drops
below VFB-ZDC, FSBH-series stops switching and the
output voltage starts to drop, which causes the feedback
voltage to rise. Once VFB rises above VFB-ZDC, switching
resumes. Burst mode alternately enables and disables
switching, thereby reducing switching loss to improve
power saving, as shown in Figure 31.
Figure 31. Burst-Mode Operation
H/L Line Over-Power Compensation
To limit the output power of the converter constantly,
high/low line over-power compensation is included.
Sensing the converter input voltage through the VIN pin,
the high/low line compensation function generates a
relative peak-current-limit threshold voltage for constant
power control, as shown in Figure 32.
Figure 32. Constant Power Control
Protections
The FSBH-series provides full protection functions to
prevent the power supply and the load from being
damaged. The protection features include:
Latch/Auto-Recovery Function
Besides the brownout protection and high/low line over-
power compensation, the FSBH0X70_F116 has
additional protections via the VIN pin, such as pull-HIGH
latch and pull-LOW auto-recovery that depends on the
application. As shown in Figure 33, when VIN level is
higher than 4.7V, FSBH-series is latched until the VDD is
discharged. FSBH-series is auto-recovery when the VIN
level is lower than 0.3V.
Figure 33. VIN Pin Function
Open-Loop / Overload Protection (OLP)
When the upper branch of the voltage divider for the
shunt regulator (KA431 shown) is broken, as shown in
Figure 34, or over current or output short occurs, there
is no current flowing through the opto-coupler transistor,
which pulls the feedback voltage up to 6V.
When feedback voltage is above 4.6V for longer than
56ms, OLP is triggered. This protection is also triggered
when the SMPS output drops below the nominal value
longer than 56ms due to the overload condition.
© 2010 Fairchild Semiconductor Corporation
FSBH0F70A_F116, FSBH0170/0270/0370_F116 • Rev. 1.0.1
13
www.fairchildsemi.com
 

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