参数资料
| 型号： | SC2440TETRT |
| 厂商： | Semtech |
| 文件页数： | 20/26页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK 2A DL 16TSSOP |
| 标准包装： | 1 |
| 类型： | 降压（降压） |
| 输出数： | 2 |
| 输入电压： | 2.8 V ~ 20 V |
| PWM 型： | 电流模式 |
| 频率 - 开关： | 1.4MHz |
| 电流 - 输出： | 2A |
| 同步整流器： | 无 |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 16-TSSOP（0.173"，4.40mm）裸露焊盘 |
| 包装： | 标准包装 |
| 供应商设备封装： | 16-TSSOP |
| 产品目录页面： | 1358 (CN2011-ZH PDF) |
| 其它名称： | SC2440TEDKR |
SC2440
POWER MANAGEMENT
Applications Information
ω Z 1 = ?
= ?
v COMP v v
v OUT
v FB
v OUT
band gain (between z 1 and p 3 ) is G MA R 5 ? ?
? ? . The
( ω C =
ω S π f
ω c 10 ω C R
= = S 1 OUT
ω p 2
This is also equal to G MP R OUT G MA R 5 ? ?
? ? . Therefore
R 5 = ? ? 1 +
23 . 3 K ? 8 . 2 × 10 6 ? 10 ? 5
10 K ? 10 ? ( 1 ) ? ( 5 . 7 ) ? ( 2 . 8 × 10 ? 4 )
?
C 5 =
10 ? 5 ? 3 . 3 V
( 1 ) ? 16 . 9 K ? ( 2 A )
In addition C 5 and R 5 form a zero with angular frequency:
1 1
R 5 C 5 15 . 4 K ? ? 470 pF
= ? 140 Krads ? 1 = ? 22 KHz
The output-to-control transfer function
= COMP ? FB is also shown in Figure 13. Its mid-
? R 2 ?
? R 1 + R 2 ?
overall loop gain T(s) is the product of the control-to-
output and the output-to-control transfer functions. To
simplify T ( j ω ) Bode plot, the feedback network is
assumed to be resistive. If the overall loop gain is to
cross 0dB at one tenth of the switching frequency
= ) at –20dB/decade, then its mid-band gain
10 5
(between z 1 and p 2 ) will be
ω S
n 10 n .
C 1 R OUT
? R 2 ?
? R 1 + R 2 ?
the crossover frequency. However it reduces the phase
margin. An estimate of R 5 and C 5 can be obtained from
(11) and (12) with n=1. The compensation is then checked
by measuring the loop gain and the phase or by observing
the inductor current and the output voltage during load
transient. Choose the largest R 5 and the smallest C 5 to
give at least 45 ° of phase margin. The corresponding
load transient should not show any ringing or excessive
overshoot (see Figures 14(c), 14(d), 17(b) and 17(c)). C 6
is a small ceramic capacitor (10-47pF) to roll off the loop
gain at high frequency. Feedforward capacitor C 11 boosts
phase margin over a limited frequency range and is
sometimes used to improve loop response. C 11 will be
more effective if R 1 >> R 1 ?? R 2 .
Example: Determine the compensation components for
the 1.3MHz 12V to 5V and 3.3V converter in Figure 1.
For both channels, ω S = 8 . 2 Mrads ? 1 , I OUT ( MAX ) = 2 A and
C 1 = 10 μ F . n is assumed to be 1 in (11) and (12).
For the 3.3V output:
?
= 16 . 9 K ?
= 1 nF
For the 5V channel:
G MP R OUT G MA R 5 ? ?
? ? =
R 7 = ? ? 1 +
40 . 2 K ? 8 . 2 × 10 6 ? 10 ? 5
10 K ? 10 ? ( 1 ) ? ( 5 . 7 ) ? ( 2 . 8 × 10 ? 4 )
? R 2 ?
? R 1 + R 2 ?
ω C 1 R OUT
10 n
.
?
?
Re-arranging,
= 25 . 5 K ?
R 5 = ? ? 1 + 1 ? ?
? R ? ω S C 1
? R 2 ? 10 nG MP G MA
(11)
C 8 =
10 ? 5 ? 5 V
( 1 ) ? 25 . 5 K ? ( 2 A )
= 1 nF
C 1 R OUT ( MIN )
C 5 = (12)
ω z1 is shown to be less than ω p2 in Figure 13. Making
ω z 1 = ω p 2 gives a first-order estimate of C 5 :
nR 5
Notice that R 5 determines the mid-band loop gain of the
converter. Increasing R 5 increases the mid-band gain and
C 6 and C 9 (both 10pF) are then added to increase gain
margin. Load transient responses of both channels are
observed using these values. There is very little inductor
current overshoot even with C 5 and C 8 reduced to 470pF
and 220pF respectively (Figure 14). The measured overall
loop gain and phase plots of the converter are also
shown.
? 2005 Semtech Corp.
20
www.semtech.com
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