参数资料
| 型号： | SC4525CSETRT |
| 厂商： | Semtech |
| 文件页数： | 12/22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.)
Output Capacitor
The output ripple voltage D V O of a buck converter can be
expressed as
Bootstrapping the Power Transistor
The minimum BST-SW voltage required to fully saturate
the power transistor is shown in Figure 5, which is about
2V at room temperature.
D V O = D I L x ? ? ESR +
? ?
?
? 8 x F SW x C O
where C O is the output capacitance.
?
?
2.2
Minimum Bootstrap Voltage
vs Temperature
Since the inductor ripple current D I L increases as D
decreases (see first inductor selection capacitor equation),
the output ripple voltage is therefore the highest when
V IN is at its maximum.
A 22μF to 47μF X5R ceramic capacitor is found adequate for
2.1
2.0
1.9
1.8
output filtering in most applications. Ripple current in the
output capacitor is not a concern because the inductor current
1.7
I SW =-3.9A
of a buck converter directly feeds C O , resulting in very low
ripple current. Avoid using Z5U and Y5V ceramic capacitors
1.6
-50
-25
0
25
50
75
100
125
Temperature ( C)
for output filtering because these types of capacitors have
high temperature and high voltage coefficients.
Freewheeling Diode
Use of Schottky barrier diodes as freewheeling rectifiers
reduces diode reverse recovery input current spikes,
easing high-side current sensing in the SC4525C. These
diodes should have an average forward current rating
at least 3A and a reverse blocking voltage of at least a
few volts higher than the input voltage. For switching
regulators operating at low duty cycles (i.e. low output
voltage to input voltage conversion ratios), it is beneficial
to use freewheeling diodes with somewhat higher
average current ratings (thus lower forward voltages). This
is because the diode conduction interval is much longer
than that of the transistor. Converter efficiency will be
improved if the voltage drop across the diode is lower.
The 20BQ030 (International Rectifier), B320A, B330A
(Diodes Inc.), SS33 (Vishay), CMSH3-20MA and CMSH3-
40MA (Central-Semi.) are all suitable.
The freewheeling diode should be placed close to the SW
pin of the SC4525C on the PCB to minimize ringing due to
trace inductance.
o
Figure 5. Typical Minimum Bootstrap Voltage required
to Saturate the Transistor (I SW = -3.9A)
The BST-SW voltage is supplied by a bootstrap circuit
powered from either the input or the output of the
converter (Figures 6(a), 6(b) and 6(c)). To maximize
efficiency, tie the bootstrap diode to the converter output
if V O > 2.5V as shown in Figures 6(a) and 6(c). Since the
bootstrap supply current is proportional to the converter
load current, using a lower voltage to power the bootstrap
circuit reduces driving loss and improves efficiency.
The bootstrap diode D can be a fast switching PN diode
( N4 48 or N9 4) if V O falls between 3V and 8V as shown
in Figure 6(a). If the converter output voltage is between
2.5V and 3V or higher than 8V, then use a low forward drop
Schottky diode (BAT54 or similar) for D (Figure 6(c)). If V O
is less than 2.5V, then it will be necessary to bootstrap the
SC4525C from V IN (Figure 6(b)). If bootstrapping from V IN
> 20V, then connect a Zener diode D 3 in series with D to
reduce the voltage stress at the BST pin. Figure 6(b) shows
this configuration for V IN > 20V. If bootstrapping from V IN <
20V, then D alone will suffice.
A small ceramic capacitor (0.33uF - 0.47uF) is adequate for
bootstrapping.
2
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