SC402B
27
Applications Information (continued)
SC402B regulates to the valley of the ripple voltage at the
FB pin, a high ripple magnitude is undesirable as it signifi-
cantly impacts the output voltage regulation. As a result,
it is desirable to select a corner frequency for (R
1
// R
2
) x C
C
to achieve enough, but not excessive, ripple magnitude
and phase margin. The component values for R
1
, R
2
, and
C
C
should be calculated using the following procedure.
Select C
L
(typical 10nF) and R
L
to match with L and DCR
time constant using the following equation.
L
L
C
DCR
L
R
Select C
C
by using the following equation.
sw
2
1
C
f
2
3
R
//
R
1
C
The resistor values (R
1
and R
2
) in the voltage divider circuit
set the V
OUT
for the switcher. The typical value for C
C
is
from 10pF to 1nF.
Dropout Performance
The output voltage adjustment range for continuous con-
duction operation is limited by the fixed 250ns (typical)
minimum off-time of the one-shot. When working with
low input voltages, the duty-factor limit must be calcu-
lated using worst-case values for on and off times.
The duty-factor limitation is shown by the next equation.
)
MAX
(
OFF
)
MIN
(
ON
)
MIN
(
ON
T
T
T
DUTY
The inductor resistance and MOSFET on-state voltage
drops must be included when performing worst-case
dropout duty-factor calculations.
System DC Accuracy (V
OUT
Controller)
Three factors affect V
OUT
accuracy: the trip point of the FB
error comparator, the ripple voltage variation with line
and load, and the external resistor tolerance. The error
comparator offset is trimmed so that under static condi-
tions it trips when the feedback pin is 750mV, 1%.
The on-time pulse from the SC402B in the design example
is calculated to give a pseudo-fixed frequency of 300kHz.
Some frequency variation with line and load is expected.
This variation changes the output ripple voltage. Because
adaptive on-time converters regulate to the valley of the
output ripple, ?of the output ripple appears as a DC regu-
lation error. For example, if the output ripple is 50mV with
V
IN
= 6 volts, then the measured DC output will be 25mV
above the comparator trip point. If the ripple increases to
80mV with V
IN
= 25V, then the measured DC output will be
40mV above the comparator trip. The best way to mini-
mize this effect is to minimize the output ripple.
The use of 1% feedback resistors may result in up to 1%
error. If tighter DC accuracy is required, 0.1% resistors
should be used.
The output inductor value may change with current. This
will change the output ripple and therefore will have a
minor effect on the DC output voltage. The output ESR
also affects the output ripple and thus has a minor effect
on the DC output voltage.
Switching Frequency Variation
The switching frequency varies with load current as a
result of the power losses in the MOSFETs and DCR of the
inductor. For a conventional PWM constant-frequency
converter, as load increases the duty cycle also increases
slightly to compensate for IR and switching losses in the
MOSFETs and inductor. An adaptive on-time converter
must also compensate for the same losses by increasing
the effective duty cycle (more time is spent drawing
energy from V
IN
as losses increase). The on-time is essen-
tially constant for a given V
OUT
/V
IN
combination, to offset
the losses the off-time will tend to reduce slightly as load
increases. The net effect is that switching frequency
increases slightly with increasing load.
发布紧急采购，3分钟左右您将得到回复。
相关PDF资料
SC403MLTRT
IC REG DL BCK/LINEAR SYNC 32MLPQ
SC418ULTRT
IC REG DL BUCK/LINEAR 20MLPQ
SC424MLTRT
IC REG DL BUCK/LINEAR 28MLPQ
SC4250LISTRT
IC HOT SWAP CTRLR 8-SOIC
SC427MLTRT
IC REG DL BUCK/LINEAR 32MLPQ
SE95D,112
IC SENSOR TEMP 2.8-5.5V SOT96-1
SE97BTP,547
IC TEMP SENSOR DIMM 8HWSON
SE98ATP,547
IC TEMP SENSOR DDR 8-HWSON
相关代理商/技术参数
SC402S
功能描述:数据转换模块 SC400 4W SERIAL OEM
RoHS:否 制造商:Lyrtech 产品:ADC and DAC FMC Modules 转换速率:250 MSPS, 1 GSPS 信噪比: ADC 输入端数量:2 DAC 输出端数量:2 分辨率:14 bit, 16 bit 接口类型:SPI 工作电源电压:3.3 V, 12 V 工作电源电流: 最大工作温度: 尺寸:84 mm x 69 mm x 10 mm
SC403
制造商:SEMTECH 制造商全称:Semtech Corporation 功能描述:6A EcoSpeedTM Integrated FET Regulator with Programmable LDO
SC403B
制造商:SEMTECH 制造商全称:Semtech Corporation 功能描述:6A EcoSpeed?? Integrated FET Regulator with Programmable LDO
SC403BEVB
制造商:SEMTECH 功能描述:Evaluation Board for 10 A EcoSpeed?Integrated FET Regulator w/ Programmable LDO
SC403BMLTRT
制造商:Semtech Corporation 功能描述:Integrated FET Regulator with Programmable LDO 32-Pin MLPQ T/R 制造商:Semtech Corporation 功能描述:6A EcoSpeed Integrated FET Regulator with Programmable LDO. PKG: MLPQ-32 制造商:Semtech 功能描述:Integrated FET Regulator with Programmable LDO 32-Pin MLPQ T/R 制造商:SEMTECH 功能描述:6A EcoSpeed step down regultor
SC403EVB
制造商:SEMTECH 制造商全称:Semtech Corporation 功能描述:6A EcoSpeedTM Integrated FET Regulator with Programmable LDO
SC403MLTRT
功能描述:IC REG DL BCK/LINEAR SYNC 32MLPQ RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - 线性 + 切换式 系列:EcoSpeed®, SmartDrive™ 标准包装:2,500 系列:- 拓扑:降压（降压）同步（3），线性（LDO）（2） 功能:任何功能 输出数:5 频率 - 开关:300kHz 电压/电流 - 输出 1:控制器 电压/电流 - 输出 2:控制器 电压/电流 - 输出 3:控制器 带 LED 驱动器:无 带监控器:无 带序列发生器:是 电源电压:5.6 V ~ 24 V 工作温度:-40°C ~ 85°C 安装类型:* 封装/外壳:* 供应商设备封装:* 包装:*
SC4040
制造商:SEMTECH 制造商全称:Semtech Corporation 功能描述:PRECISION SHUNT VOLTAGE REFERENCE