参数资料
| 型号： | FSQ500L |
| 厂商： | Fairchild Semiconductor |
| 文件页数： | 9/12页 |
| 文件大小： | 0K |
| 描述： | IC SWIT PWM GREEN UVLO SOT223 |
| 标准包装： | 1 |
| 系列： | FPS™ |
| 输出隔离： | 隔离 |
| 频率范围： | 120kHz ~ 140kHz |
| 输入电压： | 5.5 V ~ 10 V |
| 输出电压： | 700V |
| 功率（瓦特）： | 3W |
| 工作温度： | -40°C ~ 85°C |
| 封装/外壳： | TO-261-4，TO-261AA |
| 供应商设备封装： | SOT-223-3 |
| 包装： | 标准包装 |
| 其它名称： | FSQ500LFSDKR |
3.1 Overload Protection (OLP) : Overload is defined as
the load current exceeding its normal level due to an
V DS
Power
on
TSD
occurs
TSD
removed
unexpected abnormal event. In this situation, the
protection circuit should trigger to protect the SMPS.
However, even when the SMPS is in the normal
operation, the overload protection circuit can be
triggered during the load transition. To avoid this
undesired operation, the overload protection circuit is
designed to trigger after a specified time to determine
whether the situation is transient or a true overload.
Because of the pulse-by-pulse current limit capability,
the maximum peak current through the senseFET is
limited and, therefore, the maximum input power is
V CC
6.5V
6.0V
5.7V
restricted with a given input voltage. If the output
consumes more than this maximum power, the output
voltage (V O ) decreases below the set voltage. This
reduces the current through the opto-coupler LED,
which also reduces the opto-coupler transistor current,
Normal Fault Normal
operation situation operation
Figure 19. Over-Temperature Protection (OTP)
t
thus increasing the feedback voltage (V FB ). If V FB
exceeds 2.7V, D1 is blocked and the 5μA current source
starts to charge C B slowly up to V CC . In this condition,
V FB continues increasing until it reaches 4.5V, when the
switching operation is terminated, as shown in Figure
18. The delay time for shutdown is the time required to
charge C B from 2.7V to 4.5V with 5μA. In general, a 10
~ 50ms delay time is typical for most applications. This
protection is implemented in auto restart mode.
V FB Overload protection
4.5V
2.7V
4. Soft-Start : The soft-start time is tuned by an external
V CC capacitor (C A ), which increases PWM comparator
non-inverting input voltage together with the senseFET
current slowly after it starts up. Before V CC reaches
V START , C A is charged by the current I CH -I START , where I CH
and I START are described in Figure 15. After V CC reaches
V START , all internal blocks are activated, so that the
current consuming inside IC becomes I OP . Therefore, C A
is charged by the current I CH -I OP , which makes the
increasing slope of V CC become sluggish. V CC is shifted
by 6.0V negatively (it is performed in soft-start block in
Figure 2), and then V CC -6.0V is an input of one of the
input terminals of the PWM comparator. The drain
current follows V CC -6.0V instead of the V FB * because of
the low-dominant feature of the PWM comparator. The
soft-start time can be made long or short by selecting
C A , as described in Figure 20. During t S/S , I DELAY is
disabled to avoid unwanted OLP. Typically, t S/S is
around 4.6ms with 27μF of C A .
T 12 = C B *(4.5-2.7)/I DELAY
6.5V
V CC
t S/S
V CCREG
T 1
Figure 18. Overload Protection
T 2
t
6V
5V
V START
V STOP
3.2 Thermal Shutdown (TSD): The senseFET and the
control IC in one package makes it easy for the control
IC to detect an abnormal over temperature of the
t 1
t 2
t
senseFET. When the temperature exceeds
approximately 140 ° C, the thermal shutdown triggers.
When TSD triggers, delay current is disabled, switching
operation stops, and V CC through the internal high-
voltage current source is set to 5.7V from 6.5V, as
shown in Figure 19. Since TSD signal prohibits the
senseFET from switching, there is no switching until the
junction temperature decreases sufficiently. If the
junction temperature is lower than 60°C typically, TSD
signal is removed and V CC is set to 6.5V again. While
V CC increases from 5.7V to 6.5V, the soft-start function
makes the senseFET turn on and off with no voltage
and/or current stress.
? 2008 Fairchild Semiconductor Corporation
FSQ500L ? Rev. 1.0.3
9
t 1 =C A ×6V/(I CH -I START ) t S/S =C A ×0.5V/(I CH -I OP )
Figure 20. Soft-Start Function
The peak value of the drain current of 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. It
also helps to prevent transformer saturation and reduce
stress on the secondary diode during startup.
www.fairchildsemi.com
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