参数资料
| 型号： | SC419ULTRT |
| 厂商： | Semtech |
| 文件页数： | 11/24页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM 20-MLPQ |
| 标准包装： | 1 |
| 系列： | EcoSpeed®, SmartDrive™ |
| PWM 型： | 控制器 |
| 输出数： | 1 |
| 频率 - 最大： | 1MHz |
| 电源电压： | 3 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： | 20-MLPQ |
| 包装： | 标准包装 |
| 其它名称： | SC419ULTRTDKR |
SC419
Applications Information
General Description
The SC419 is a step down synchronous DC-DC buck con-
troller. It provides high efficiency operation in a space
saving 3 x 3 (mm) 20-pin package. The programmable
operating frequency range from 200kHz to 1MHz enables
optimizing the configuration for PCB area and efficiency.
V IN . The period is proportional to output voltage and
inversely proportional to input voltage. With this adaptive
on-time configuration, the device automatically antici-
pates the on-time needed to regulate V OUT for the present
V IN condition and at the selected frequency.
The advantages of adaptive on-time control are:
The controller uses a pseudo-fixed frequency adaptive
on-time control. This allows fast transient response which
permits the use of smaller output capacitors.
Input Voltage Requirements
The SC419 requires three input supplies for normal opera-
tion: V IN , VDDA, and VDDP. V IN can operate over the wide
range of 3V to 28V. VDDA and VDDP require an external
5V supply. VDDA and VDDP should be connected to the
same source voltage.
Psuedo-fixed Frequency Adaptive On-time Control
The PWM control method used by the SC419 is pseudo-
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Predictable operating frequency compared to
other variable frequency methods.
Reduced component count by eliminating the
error amplifier and compensation components.
Reduced component count by removing the
need to sense and control inductor current.
Fast transient response — the response time is
controlled by a fast comparator instead of a typi-
cally slow error amplifier.
Reduced output capacitance due to fast tran-
sient response.
fixed frequency, adaptive on-time, as shown in Figure 1.
The ripple voltage generated at the output capacitor ESR
is used as a PWM ramp signal. This ripple is used to trigger
the on-time of the controller.
One-Shot Timer and Operating Frequency
One-shot timer operation is shown in Figure 2. The FB
comparator output goes high when V FB is less than the
internal 500mV reference. This feeds into the gate drive
and turns on the high-side MOSFET, and also starts the
V I N
Q1
V LX
C IN
L
TON
V FB
V LX
FB Threshold
V OUT
one-shot timer. The one-shot timer uses an internal com-
parator and a capacitor. One comparator input is con-
nected to V OUT , the other input is connected to the
capacitor. When the on-time begins, the internal capaci-
tor charges from zero volts through a current which is
proportional to V IN . When the capacitor voltage reaches
V OUT , the on-time is completed and the high-side MOSFET
turns off.
+
FB
500mV
Q2
ESR
C OUT
FB
FB Comparator
-
+
Gate
Drives
DH
V IN
Q1
V LX
L
V OUT
DL
Figure 1 — PWM Control Method, V OUT Ripple
The adaptive on-time is determined by an internal one-
V OUT
V IN
R TON
One-Shot Q2
Timer
On-time = K x R TON x (V OUT /V IN )
ESR
C OUT
+
FB
shot timer. When the one-shot is triggered by the output
ripple, the device sends a single on-time pulse to the high-
Figure 2 — On-Time Generation
side MOSFET. The pulse period is determined by V OUT and
11
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