参数资料
型号: FSL116HR
厂商: Fairchild Semiconductor
文件页数: 11/13页
文件大小: 0K
描述: IC FPS SWITCH PWM/SENSEFET 8MDIP
标准包装: 50
系列: FPS™
输出隔离: 隔离
频率范围: 90kHz ~ 110kHz
输入电压: 9 V ~ 26 V
输出电压: 650V
功率(瓦特): 16W
工作温度: -40°C ~ 105°C
封装/外壳: 8-DIP(0.300",7.62mm)
供应商设备封装: 8-MDIP
包装: 管件
Output-Short Protection (OSP)
If the output is shorted, steep current with extremely
high di/dt can flow through the SenseFET during the
LEB time. Such a steep current brings high-voltage
stress on the drain of SenseFET when turned off. To
protect the device from such an abnormal condition,
OSP detects V FB and SenseFET turn-on time. When the
V FB is higher than 1.6V and the SenseFET turn-on time
is lower than 1.0μs, the FPS recognizes this condition
as an abnormal error and shuts down PWM switching
until V CC reaches V START again. An abnormal condition
output is shown in Figure 20.
Figure 20. Output Short Waveforms (OSP)
Soft-Start
The FPS has an internal soft-start circuit that slowly
increases the feedback voltage, together with the
SenseFET current, after it starts. The typical soft-start
time is 20ms, as shown in Figure 21, where progressive
increments of the SenseFET current are allowed during
the startup phase. The pulse width to the power
switching device is progressively increased to establish
the correct working conditions for transformers,
inductors, and capacitors. The voltage on the output
capacitors is progressively increased with the intention
of smoothly establishing the required output voltage.
Soft-start helps to prevent transformer saturation and
reduces the stress on the secondary diode.
continues, but the current limit is fixed internally to
minimize flux density in the transformer. The fixed
current limit is larger than that defined by V FB = V BURH
and, therefore, V FB is driven down further. Switching
continues until the feedback voltage drops below V BURL .
At this point, switching stops and the output voltages
start to drop at a rate dependent on the standby current
load. This causes the feedback voltage to rise. Once it
passes V BURH , switching resumes. The feedback voltage
then falls and the process repeats. Burst Mode
alternately enables and disables switching of the
SenseFET and reduces switching loss in Standby Mode.
Figure 22. Burst-Mode Operation
Adjusting Peak Current Limit
As shown in Figure 23, a combined 6k ? internal
resistance is connected to the non-inverting lead on the
PWM comparator. An external resistance of Rx on the
current limit pin forms a parallel resistance with the 6k ?
when the internal diodes are biased by the main current
source of 400μA. For example, FSL116HR has a typical
SenseFET peak current limit (I LIM ) of 1.1A. I LIM can be
adjusted to 0.8A by inserting Rx between the I PK pin and
the ground. The value of the Rx can be estimated by the
following equations:
Figure 21. Internal Soft-Start
Burst Mode Operation
To minimize power dissipation in Standby Mode, the
FPS enters Burst Mode. As the load decreases, the
feedback voltage decreases. As shown in Figure 22, the
1.1A : 0.8A = 6kΩ : XkΩ
X = Rx || 6kΩ
where X is the resistance of the parallel network.
(1)
(2)
device automatically enters Burst Mode when the
feedback voltage drops below V BURH . Switching
? 2010 Fairchild Semiconductor Corporation
FSL116HR ? Rev. 1.0.1
11
Figure 23. Peak Current Limit Adjustment
www.fairchildsemi.com
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