参数资料
| 型号： | SC4524DSETRT |
| 厂商： | Semtech |
| 文件页数： | 10/22页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK ADJ 2A 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 ~ 17.28 V |
| 输入电压： | 3 V ~ 18 V |
| PWM 型： | 电流模式 |
| 频率 - 开关： | 300kHz ~ 1.3MHz |
| 电流 - 输出： | 2A |
| 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： | SC4524DSEDKR |
SC4524D
Applications Information (Cont.)
becomes armed. As the load draws more current from
Table 3: Resistor for Typical Switching Frequency
the regulator, the current-limit comparator ILIM (Figure
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
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
? 1 ? ?
R 4 = R 6 ?
V O + V D
V IN + V D ? V CESAT
D I L =
Fig.4
This current V ramp D is ( absent unless the switch is turned
on. The intersection I ? O of F SW this ramp with the output of the
L 1 =
a period of time, then the soft-start capacitor will be
discharged below 1.9V. 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
1.0V. At this moment, the overload latch is reset. The
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.
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.
Minimum On Time Consideration
? V O
The operating duty cycle of a non-synchronous step-
1 . ? ?
down switching 0 V regulator in continuous-conduction
mode (CCM) is given by
D =
where V CESAT is the switch saturation voltage and V D is
voltage drop across the rectifying diode.
( V O + V D ) ? ( 1 ? D )
F SW ? L 1
In peak current-mode control, the PWM modulating
ramp is the sensed current ramp of the power switch.
20 % ?
voltage feedback error amplifier determines the switch
A C =
A C =
R 7 =
C 5 =
C 8 =
S minimum controllable switch on time (T
).
During normal operation, the soft-start capacitor is
charged to 2.4V.
CIN = I O D ( 1 ? ? ? D ) I RMS _
pulse width. The propagation delay time required to
immediately turn off the switch after it is turned on is the
S 270 RE V 6-7
ON(MIN)
V o
V c
=
R 4 = R 6 ? ?
? 1 ? ?
Setting D the Switching Frequency
V O + V D
G PWM
D V O = D I L ? ? ? ESR +
?
? 8 ? F SW ? C O ?
R 7 =
A C = ? 20 ? log ? ?
? FB ? ?
?
C IN > 140
1 . 0 C ? 5 =
? ? D V IN ? F 1 SW
A C = ? 20 ? log ?
4 1
? 28 ? 6 . 1 ? 10 ? 3 2 π ? 80 ? 10 3 ? 22 ? 10 ? 6 3 . 3 ?
C 8 =
10 100 -50 -25
R 7 =
= 22 . 3 0 k 25
SettingtheOutputVoltage
The regulator output voltage is set with an external
resistive divider (Figure 1) with its center tap tied to the
FB pin. For a given R 6 value, R 4 can be found by
V O
? 1 . 0 V ?
=
V IN + V D ? V CESAT
The switching frequency of the SC4524D is set with an
external resistor from the ROSC pin to ground. Table 3
Minumum On Time vs Temperature
200 ? 1 ?
180 V O = 1.5V , I O = 1A , 1M Hz
? 1 1 V ?
160 ? G CA R S 2 π F C C O V O ?
I O
? ? ? = 15
120
15 . 9
20
50 75 100 125
0 . 28 ? 10 ? 3 Temperature ( O C)
lists standard resistor ) values D for typical frequency setting.
F SW ? L 1
( V O + V D ) ? ( 1 ? D )
20 % ? I O ? F SW
= 0 . 45 nF
2 π Figure 4. ? 22 . 1 ? 10 3
? 16 ? 10
= 12 pF
D I L =
L 1 =
C 5 =
C 8 =
1
3 Variation of Minimum On Time
with Ambient Temperature
1
2 π ? 600 ? 10 3 ? 22 . 1 ? 10 3
10
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