参数资料
| 型号： | SC470ITSTRT |
| 厂商： | Semtech |
| 文件页数： | 16/31页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM 14-TSSOP |
| 标准包装： | 1 |
| PWM 型： | 控制器 |
| 输出数： | 1 |
| 电源电压： | 5 V ~ 5.5 V |
| 降压： | 是 |
| 升压： | 无 |
| 回扫： | 无 |
| 反相： | 无 |
| 倍增器： | 无 |
| 除法器： | 无 |
| Cuk： | 无 |
| 隔离： | 无 |
| 工作温度： | -40°C ~ 125°C |
| 封装/外壳： | 14-TSSOP（0.173"，4.40mm 宽） |
| 包装： | 标准包装 |
| 产品目录页面： | 1358 (CN2011-ZH PDF) |
| 其它名称： | SC470ITSDKR |
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NOT RECOMMENDED FOR NEW DESIGN
POWER MANAGEMENT
Application Information (Cont.)
SC470
Figure 7 below shows recommended components that
work well.
VPULLUP
R8
10k
R9 1k Q3
VGATE
C11
22n
Figure 7: Recommended Component Values
Please see the example switching waveforms on Pages
25 and 26.
Thermal Considerations
The junction temperature of the device may be calculated
as follows:
Inserting the following values for VBAT (MIN) condition (since
this is the worst-case condition for power dissipation in
the controller) as an example (VOUT = 1.2V):
T A = 85°C
θ JA = 100°C/W (For TSSOP-14)
θ JA = 46°C/W (For MLPQ-16)
VCCA = VDDP = 5V
I VCCA = 1100μA (data sheet maximum)
I VDDP = 150μA (data sheet maximum)
V g = 5V
Q g = 60nC
f = 266kHz
VBAT (MIN) = 8V
VBST (MIN) = VBAT (MIN) +VDDP = 13V
D (MIN) = 1.2/8 = 0.15
gives us:
P D = 5 ? 1100 ? 10 ? 6 + 5 ? 150 ? 10 ? 6
+ 5 ? 60 ? 10 ? 9 ? 266 ? 10 3 + 13 ? 1 ? 10 ? 3 ? 0 . 15
= 0 . 088 W
T J = T A + P D ? θ JA
° C
Where:
T A = ambient temperature (°C)
P D = power dissipation in (W)
θ JA = thermal impedance junction to ambient from
absolute maximum ratings (°C/W)
So for TSSOP-14,
T J = 85 + 0 . 088 ? 100 = 93 . 8
And for MLPQ-16,
T J = 85 + 0 . 088 ? 46 = 89 . 0
° C
° C
As can be seen, the heating effects due to internal power
The power dissipation may be calculated as follows:
dissipation are practically negligible, thus requiring no
special consideration thermally during layout.
P D = VCCA ? I VCCA + VDDP ? I VDDP
+ V g ? Q g ? f + VBST ? 1 mA ? D
W
Where:
VCCA = chip supply voltage (V)
I VCCA = operating current (A)
VDDP = gate drive supply voltage (V)
I VDDP = gate drive operating current (A)
V g = gate drive voltage, typically 5V (V)
Q g = FET gate charge, from the FET datasheet (C)
f = switching frequency (kHz)
VBST = boost pin voltage during t ON (V)
D = duty cycle
? 2005 Semtech Corp.
16
www.semtech.com
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