参数资料
| 型号： | SC4525DSETRT |
| 厂商： | Semtech |
| 文件页数： | 11/21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 ~ 16.74 V |
| 输入电压： | 3 V ~ 18 V |
| PWM 型： | 电流模式 |
| 频率 - 开关： | 65kHz ~ 350kHz |
| 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： | SC4525DSEDKR |
R 4 = R 6 ? ?
? ? ?
V O + V D
Inductor V Selection CESAT
R D 4 I L = = R 6 ? O O D ? ?
the inductance. + O V + D V ) D ? ( ? D )
D L = =
among efficiency, cost ( and size. Re-arranging the previous
euqation and assuming 35% inductor ripple current, the
inductor 4 = is R given V O by ? ? ?
F SW ? L
?
( V O + V ? D ) ? ( ? D )
? . 0 V ?
L D V = O = D ? I L V ? O ? ? ESR + ?
?
R 4 = R 6 35 % ? ? I O ? ? SW 8 ? F SW ? C O ?
? V O . 0 + V V D ?
If the input V IN voltage ? varies over a wide range, then choose
I D = _ CIN = V I O O ? V D D ? ( ? D )
converter operation at the input voltage extremes.
V + V D I O ? V CESAT
C IN > IN
D = 4 ? O D V IN D ? F SW
The peak I L current limit of SC4525D power transistor is at
F SW ? L
SC4525D I V L O is 3.9A ? + ? ? V minus 8 ? one half C of ? ? the inductor ripple
least 3.9A. The maximum deliverable load current for the
D = D I O ESR + D )
? F SW ? O ?
?
current. L = ( V O + F V SW ) ? ? ( L ? D )
20 % ? I O ? F SW
Input L Decoupling ) ? Capacitor
=
C I RMS > _ CIN =
The input capacitor O should be chosen to handle the RMS
ripple current ? of V I a O buck converter. This value is given by
4 D
? F
D V = D I L ? ? ? ESR +
?
8 ? F SW ? C O ? ?
?
?
?
in reducing = the L I ? conductive EMI from the regulator. The
? ? ESR +
?
D V O
D
C IN >
where C D IN V IN > is the allowable input ripple voltage.
V O + V D
V IN + V D ? V CESAT
SC4525D
A C = ? 20 ? log ? ?
? FB ? ?
?
? G CA R S 2 π F C C O
V O ?
. 0 ? C 5 =
D I L = ? O
( V + V D ) ? ( ? D )
A C = ? 20 ? log ?
?
?
? = 5
F SW ? L
( V O + V D ) ? ( ? D )
2.2μF) L can = be placed in parallel with a low ESR electrolytic
capacitor to satisfy ? I O both the ESR and bulk capacitance
? F SW
0 20 ? 20 %
A requirements. ? ? ? 3
28 0 G R ? 2 π F C ? V ? ?
= ? 0 . 20 ? ? log
? CA S
O ?
V o
=
2 π ? 6 ? 0 ? 22 . ? 0
A The ? output log ripple voltage D ? 3 V O ? of a buck converter can ? be ? ? = 5
=
20 ?
?
? 28 ? 6 . ? 0
2 π ? 80 ? 0 ? 22 ? 0
3 . 3 ?
C expressed as
2 π ? 600 ? 0 ? ? 22 . ? 0
? G PWM
D V O 5 . = 9 D I L ? ? ? ESR +
? ?
R 7 = = 22 . 3 k
V where C ? is the output capacitance.
= 0 . 28 O 0 PWM
? ) ( + s / ω Q + s 2 / ω V FB ) ?
2 R 7 =
V A c = ( ? 20 s ? / log p ?
? . 45 n nF ? ?
? n
Since 2 π the ? inductor S . ripple F 3 C C current O ? D I L increases as D
? 6 0 ? G CA I ? 22
? 2 0
? V FB ?
decreases > (refer to the first equation in the Inductor
C IN
C 5 =
C G A Selection ? section), R the 2 output O ? = ripple ? voltage ω Z is = therefore , . 0 ? = 5
A C = ? 20 R log ? ? D V IN ? F SW ? ?
C = 2 π G 600 R ? S 0
PWM ≈ 20 log ? , G CA S ω F ≈ C 2 pF ? ?
the highest when V ? ? 22 . is . at 0 0 ? 3 maximum. ? 0 3 ? 22 ? R 0 ESR ? 6 C O 3 . 3 ?
? its R C 2 O π ? 80
? CA ?
C 8 =
= 0 20 ? log ?
?
?
?
? = 5
A A C 22μF 20 to 47μF X5R ceramic 3 capacitor is found adequate
5 . 9 ? 28 ? + 6 s . ? 0
R ESR C O ) 2 π ? 80 ? 0 ? 22 ? 0
3 . 3 ?
R V o 7 =
G PWM (
7 = ( + s / ω p
= + 22 / . ω k n Q + s 2 / ω
V R in the output ? ) ( 3 capacitor is not a n 2 ) concern because the
s 3
0 . 28 ? 0
C inductor current of a buck converter directly feeds C O ,
5 =
= 2 π F
R C resulting Z in R 7 very low ripple = current. Avoid using Z5U
7 5 =
= 22 . 3 k
0 . 45 nF
0 2 . π 28 ? 6 0 ? 0 3 3 ? 22 . ? 0 3
R ?
G and Y5V ceramic capacitors for output filtering because ,
C thesetypesofcapacitorshavehightemperatureandhigh
C C 8 5 = = 2 π F R
= = 0 . 2 pF
= G CA ? R S R C O R ESR C O
45 nF
voltage π A C ? ? coefficients. ? 22 22 . . ? 0 0 3
2 2 π 6 ? 7 0 0 3 ?
8
R C 7 = =
g π m ? 600 ? 0 3 ? 22 .
Freewheeling Diode ? 0 3
G PWM ( + s R ESR C O )
V Use of Schottky barrier diodes as freewheeling rectifiers
=
( / ω p
C V reduces + s diode ) ( reverse ω n Q + s / ω n input current spikes,
+ s /
recovery )
5 =
easing high-side current sensing in the SC4525D. These
=
diodes + should ( have / an n average ω forward current rating
R
8 = ≈
C G at least 3A and , a reverse blocking voltage ω of = at least a ,
ω p ≈ ,
R ? R 7
PWM 2 π F
G P CA
R C O
R ESR C O
few volts higher than the input voltage. For switching
G regulators operating at ω low ≈ duty , cycles (i.e. ω Z low output ,
PWM ≈
=
,
p
voltage G to ? input voltage conversion ratios), it is beneficial
0 CA R S
R C O
R ESR C O
R 7 =
to use m freewheeling diodes with somewhat higher
average 20 current ratings (thus lower forward voltages). This
0
5 = g
2 π m F Z R 7
C C improved if the voltage drop across the diode is lower.
5 =
2 π F Z P R R 7 7
C (Diodes Inc.), SS33 (Vishay), CMSH3-20MA and CMSH3-
2 π F P R 7
V O
? . 0 V ?
Applications Information (Cont.)
D =
IN + V D ? V
The inductor ripple current for a non-synchronous step-
down converter in continuous-conduction mode is
( V ? V + V ) ? ( ? ? D)
? . 0 F V SW ? L ?
where F SW is the switching frequency (350kHz) and L is
( V O V
V ? I O ? F SW + D
V IN 20 % ? V CESAT
An inductor ripple current between 20% to 50% of the
maximum load current, I O , gives a good compromise
R 6 ?
?
D =
+ V D V CESAT
L based on the + nominal input voltage. Always verify
RMS
( V + V ) ? ( ? D )
D =
D
( V O + V D ( ? D )
IN ? D ? ( ? D )
IN SW
I RMS _ CIN = I O ? D ? ( ? D)
? ?
The input O capacitance must also be high enough to keep
input ripple voltage within specification. This is important
8 ? F SW ? C O ? ? ?
input capacitance can be estimated from
I O
4 ? D V IN ? F SW
I O
4 ? D V IN ? F SW
Multi-layer ceramic capacitors, which have very low ESR (a
few m W ) and can easily handle high RMS ripple current, are
the ideal choice for input filtering. A single 4.7μF to 0μF
X5R ceramic capacitor is adequate for most applications.
D =
? V ?
R 7 =
? 28 ? 6 . ? 0 ? 3 2 π ? 80 ? 0 3 ? 22 ? 0 ? 6 3 . 3 ?
C 8 =
5 . 9
R 7 = = 22 . 3 k V FB ?
C
C O
I RMS _ CIN = 3 I O ? 3 ) 5 =
C Output Capacitor D ? ( ? D = 0 . 45 nF V c
? . 0
C 3 ? 6
8 = 3 3 = 2 pF
0 20 ? 8 ? F SW ? C O ?
o G ? 3 ( + s R ESR C O )
+ ω
C 5 C = ? 3 R π = O 0 V
O
6
? 28 IN ?
A C ? . 0 ?
? 3 ? 6
= g m 0 20
for output filtering in most applications. Ripple current
c
5 . 9
0 20
?
PWM ≈ , ω p ≈ , ω Z =
P 3 3
600 ? ?
0 20
8 = 2 pF
2
o
2 2
c
o
c
Z
S
R
A C
20
A C
R 7 =
C is because the diode conduction interval is much longer
than that of the transistor. Converter efficiency will be
8 = 2 π F
The 20BQ030 (International Rectifier), B320A, B330A
40MA (Central-Semi.) are all suitable.
For high voltage applications, a small ceramic ( μF or
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