FSBH0F70A Fairchild Semiconductor, FSBH0F70A Datasheet - Page 12

• Manufacturer Part Number: FSBH0F70A
• Description: Fsbh0f70a, Fsbh0170/a, Fsbh0270/a, Fsbh0370 Green Mode Fairchild Power Switch Fps?
• Manufacturer: Fairchild Semiconductor

© 2009 Fairchild Semiconductor Corporation
FSBH0F70A, FSBH0170/A, FSBH0270/A, FSBH0370 • Rev. 1.0.0
Functional Description
Startup Current
For startup, the HV pin is connected to the line input or
bulk capacitor through the external resistor R
startup current drawn from HV pin is 3.5mA and it
charges the V
startup current turns off when the V
reaches to V
V
provides the operating current.
Slope Compensation
The FSBH series is designed for flyback power
converters. The peak-current-mode control is used to
optimize system performance. Slope compensation is
added to stabilize the current loop. The FSBH series
inserts a synchronized, positively sloped ramp at each
switching cycle.
Soft-Start
The FSBH series has internal soft-start circuit that
slowly increases the sense-FET current after startup.
The typical soft-start time is 5ms during which the V
level is increased six steps to smoothly establish the
required output voltage, as shown in Figure 28. This
also helps prevent transformer saturation and reduces
the stress on the secondary diode during startup.
Brown In/Out Function
Figure 27 shows a resistive divider with low-pass
filtering for line-voltage detection on the VIN pin. The
V
the V
500ms.
FSBH0170/0270/0370 turns on when V
DD
IN
Figure 27. Brown In/Out Function on VIN Pin
voltage is used for the brownout protection, when
before the auxiliary winding of the transformer
IN
voltage drops below 0.6V and debounce is
Figure 26. Soft-Start Function
With
DD-ON
DD
capacitor through the resistor R
. The V
a
DD
hysteresis
capacitor then maintains the
DD
capacitor voltage
IN
voltage,
reaches 1.1V.
HV
. Typical
HV
. The
Limit
the
12
Constant Power Control
To limit the output power of the converter constantly,
high/low line 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 28.
Latch/Auto Recovery Function
Besides the brownout protection and high/low line
compensation, the FSBH0170/0270/0370 has additional
protections, such as pull HIGH latch and pull LOW
auto-recovery that depends on the application. As
shown in Figure 29, when the V
4.7V, FSBH series is latched until the V
discharged. FSBH series is auto-recovery when the V
level is lower than 0.3V.
Protections
The FSBH-series provides full protection functions to
prevent the power supply and the load from being
damaged. The protection features include:
Over-Temperature Protection. The sense-FET and
the control IC are integrated, making it easier to
detect the temperature of the sense-FET. When the
temperature exceeds approximately 142°C, thermal
shutdown is activated.
V
disabled whenever V
threshold of 28V.
Open-Loop Protection. The FSBH series detects
the feedback signal on FB pin. When over current
or short circuit occurs, FB is pulled HIGH. After a
56ms debounce time, FSBH series is turned off.
DD
Figure 28. Constant Power Control
Over-Voltage Protection. The FSB Hseries is
Figure 29. VIN Pin Function
DD
exceeds the over-voltage
IN
level is higher than
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DD
is
IN