参数资料
| 型号： | SC2544TSTRT |
| 厂商： | Semtech |
| 文件页数： | 10/22页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM VM 24TSSOP |
| 标准包装： | 1 |
| PWM 型： | 电压模式 |
| 输出数： | 2 |
| 频率 - 最大： | 300kHz |
| 占空比： | 90% |
| 电源电压： | 4.5 V ~ 28 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 ~ 85°C |
| 封装/外壳： | 24-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： | SC2544TSDKR |
SC2544
POWER MANAGEMENT
Applications Information (Cont.)
& 5 Z Z
,
,
' >
' @
5 5 5 5 Z & & 5 & 5 &
5 5 Z & & & &
where R 1a and C 1a are the ESR and capacitance of
electrolytic capacitors, and R 1b and C 1b are the ESR
and capacitance of the ceramic capacitors, respectively
(Figure 5).
Figure 5. Equivalent RC branch.
Req and Ceq are both functions of frequency. For
rigorous design, the equivalent ESR should be
evaluated at the ripple frequency for voltage ripple
calculation when both ceramic and electrolytic
capacitors are used. If R 1a = R 1b = R 1 and C 1a = C 1b = C 1 ,
then R eq and C eq will be frequency-independent and
R eq = 1/2 R 1 and C eq = 2C 1 .
Input Capacitor (Cin)
The input supply to the converter usually comes from
a pre-regulator. Since the input supply is not ideal,
input capacitors are needed to filter the current pulses
at the switching frequency. A simple buck converter
is shown in Figure 6.
Figure 6. A simple model for the converter input.
In Figure 6 the DC input voltage source has an internal
impedance R in and the input capacitor C in has an ESR
of R esr . MOSFET and input capacitor current
waveforms, ESR voltage ripple and input voltage ripple
are shown in Figure 7.
L
L
9
9
Figure 7. Typical waveforms at converter input.
It can be seen that the current in the input capacitor
pulses with high di/dt. Capacitors with low ESL should
be used. It is also important to place the input capacitor
close to the MOSFETs on the PC board to reduce trace
inductances around the pulse current loop.
The RMS value of the capacitor current is
approximately
G ' '
K K
The power dissipated in the input capacitors is then
P Cin = I Cin2 R esr .
For reliable operation, the maximum power dissipation
in the capacitors should not result in more than 10 o C
of temperature rise. Many manufacturers specify the
maximum allowable ripple current (ARMS) rating of
the capacitor at a given ripple frequency and ambient
temperature. The input capacitance should be high
enough to handle the ripple current. It is common
pratice that multiple capacitors are placed in parallel
to increase the ripple current handling capability.
? 2005 Semtech Corp.
12
www.semtech.com
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