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参数资料
| 型号： | SC202AMLTRT |
| 厂商： | Semtech |
| 文件页数： | 13/19页 |
| 文件大小： | 0K |
| 描述： | IC STEP DOWN SWTCHNG REG 13VFQFN |
| 标准包装： | 1 |
| 系列： | SC202 |
| 类型： | 非隔离（POL） |
| 输出数： | * |
| 电压 - 输入（最小）： | * |
| 电压 - 输入（最大）： | * |
| Voltage - Output 1： | * |
| Voltage - Output 2： | * |
| Voltage - Output 3： | * |
| 电流 - 输出（最大）： | * |
| 电源（瓦） - 制造商系列： | * |
| 特点： | * |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 13-VFQFN 裸露焊盘 |
| 尺寸/尺寸： | 0.12" L x 0.10" W x 0.04" H（3.0mm x 2.5mm x 1.0mm） |
| 包装： | 标准包装 |
| 工作温度： | * |
| 效率： | * |
| 电源（瓦特）- 最大： | * |
| 其它名称： | SC202AMLDKR |
SC202A
Applications Information (continued)
The resistor values can be determined using the following
equation.
10kΩ, and include a feed-forward capacitance calculated
with the previous equation. If the output voltage is set to
1.0V, the previous equation reduces to the following
V OUT
V SET
R FB1 R FB 2
R FB 2
I SNS R FB 1
equation.
V OUT
0 . 5
C FF
8 10
whereV OUT isthedesiredoutputvoltage,V SET isthevoltage
setting selected by the CTL pins, R FB1 is the resistor
between the output capacitor and the SNS pin, R FB2 is the
resistor between the SNS pin and ground, and I SNS is the
leakage current into the SNS pin during normal operation.
The current into the SNS pin is typically 1μA, so the last
term of the equation can be neglected if the current
through R FB2 is much larger than 1μA. Selecting a resistor
value of 10kΩ or lower will simplify the design. If I SNS is
neglected and R FB2 is fixed, R FB1 can be determined using
the following equation.
2
6
R FB 1 V OUT 1
Example:
An output voltage of 1.3V is desired, but this is not a pro-
grammable option. What external component values for
Figure 1 are needed?
Solution: To keep the circuit simple, set R FB2 to 10kΩ so
current into the SNS pin can be neglected and set the
CTL3-0 pins to 0010 (1.0V setting). The necessary compo-
nent values for this situation are shown by the following
V OUT V SET
V SET
R FB 1 R FB 2
Inserting resistance in the feedback loop will adversely
equations.
R FB 1 R FB 2
V OUT V SET
V SET
3 k
affect the system’s transient performance if feed-forward
capacitance is not included in the circuit. The circuit in
Figure 1 illustrates how the resistor divider and feed-
C FF
8 10
6
V OUT 0 . 5
R FB 1 V OUT
2
1
5 . 69 nF
forward capacitor can be added to the SC202A
schematic.
PWM Operation
Normal PWM operation occurs when the output load
V IN
C IN
IN
SC202A
OUT
C OUT
V OUT
current exceeds the PSAVE threshold. In this mode, the
PMOS high side switch is activated with the duty cycle
required to produce the output voltage programmed by
C FF
the CTL pins. An internal synchronous NMOS rectifier
Enable
CTL3
CTL2
CTL1
CTL0
SNS
GND
R FB1
R FB2
eliminates the need for an external Schottky diode on
the LX pin. The duty cycle (percentage of time PMOS is
active) increases as V IN decreases to maintain output
voltage regulation. As the input voltage approaches the
programmed output voltage, the duty cycle approaches
Figure 1 – Application Circuit with External Resistors
The value of feed-forward capacitance needed can be
determined using the following equation.
100% (PMOS always on) and the device enters a pass-
through mode until the input voltage increases or the
load decreases enough to allow PWM switching to
resume.
V SET V OUT
0 . 5
C FF
4 10
6
R FB 1
V OUT V SET V SET
2
0 . 5
Power Save Mode Operation
When the load current decreases below the PSAVE
threshold, PWM switching stops and the device auto-
To simplify the design, it is recommended to program the
output setting to 1.0V, use resistor values smaller than
matically enters PSAVE mode. This threshold varies
depending on the input voltage and output voltage
13
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