参数资料
| 型号： | SC4525CSETRT |
| 厂商： | Semtech |
| 文件页数： | 10/22页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK ADJ 3A 8SOIC |
| 标准包装： | 1 |
| 类型： | 降压（降压） |
| 输出类型： | 可调式 |
| 输出数： | 1 |
| 输出电压： | 1 V ~ 26.88 V |
| 输入电压： | 3 V ~ 28 V |
| PWM 型： | 电流模式 |
| 频率 - 开关： | 300kHz ~ 1.3MHz |
| 电流 - 输出： | 3A |
| 同步整流器： | 无 |
| 工作温度： | -40°C ~ 105°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 8-SOIC（0.154"，3.90mm Width）裸露焊盘 |
| 包装： | 标准包装 |
| 供应商设备封装： | 8-SOIC-EP |
| 其它名称： | SC4525CSEDKR |
SC4525C
Applications Information (Cont.)
becomes armed. As the load draws more current from
the regulator, the current-limit comparator ILIM (Figure
Table 3: Resistor for Typical Switching Frequency
2) will eventually limit the switch current on a cycle-by-
cycle basis. The over-current signal OC goes high, setting
the latch B 3 . The soft-start capacitor is discharged with
(I D - I C ) (Figure 3). If the inductor current falls below the
current limit and the PWM comparator instead turns off
the switch, then latch B 3 will be reset and I C will recharge
the soft-start capacitor. If over-current condition persists
or OC becomes asserted more often than PWM over
a period of time, then the soft-start capacitor will be
Freq. (k)
200
250
300
350
400
500
600
R OSC (k)
110
84.5
69.8
57.6
49.9
38.3
30.9
Freq. (k)
700
800
900
1000
1100
1200
1300
R OSC (k)
25.5
21.5
18.2
15.8
14.0
12.4
11.0
Freq. (k)
1400
1500
1600
1700
1800
1900
2000
R OSC (k)
9.76
8.87
8.06
7.15
6.34
5.62
5.23
discharged below .9V. At this juncture, comparator B 4
sets the overload latch B 2 . The soft-start capacitor will be
continuously discharged with (I D - I C ). The COMP pin is
immediately pulled to ground. The switching regulator is
shut off until the soft-start capacitor is discharged below
.0V. At this moment, the overload latch is reset. The
Minimum On Time Consideration
The operating duty cycle of a non-synchronous step-
down switching regulator in continuous-conduction
mode (CCM) is given by
soft-start capacitor is recharged and the converter again
undergoes soft-start. The regulator will go through soft-
start, overload shutdown and restart until it is no longer
overloaded.
D =
V O + V D
V IN + V D ? V CESAT
If the FB voltage falls below 0.8V because of output
overload, then the switching frequency will be reduced.
Frequency foldback helps to limit the inductor current
when the output is hard shorted to ground.
During normal operation, the soft-start capacitor is
charged to 2.4V.
Setting the Output Voltage
The regulator output voltage, V O , is set with an external
resistive divider (Figure ) with its center tap tied to the FB
pin. For a given R 6 value, R 4 can be found by
where V IN is the input voltage, V CESAT is the switch saturation
voltage, and V D is voltage drop across the rectifying
diode.
In peak current-mode control, the PWM modulating
ramp is the sensed current ramp of the power switch.
This current ramp is absent unless the switch is turned
on. The intersection of this ramp with the output of the
voltage feedback error amplifier determines the switch
pulse width. The propagation delay time required to
immediately turn off the switch after it is turned on is the
minimum controllable switch on time (T ON(MIN) ).
Closed-loop measurement shows that the SC4525C
R 4 = R 6 ?
? ?
? V O
? . 0 V
?
?
minimum on time is about 20ns at room temperature
(Figure 4). If the required switch on time is shorter than
the minimum on time, the regulator will either skip cycles
Setting the Switching Frequency
or it will jitter.
The switching frequency of the SC4525C is set with an
external resistor from the ROSC pin to ground. Table 3 lists
the standard resistor values for typical frequency setting.
0
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