参数资料
| 型号： | SC419ULTRT |
| 厂商： | Semtech |
| 文件页数： | 13/24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 (continued)
maintain the desired on-time. On-time is calculated
according to the voltage at the VOUT pin.
The equation for determining the R PSV resistor value is
shown next. The desired minimum frequency is f SWMIN .
Programmable Ultra-sonic Power-Save Operation
The device provides programmable ultra-sonic power-
R PSV
1
350 pF f SWMIN
save operation at light loads. The minimum operating fre-
quency is programmed by connecting a resistor from PSV
to AGND. The SC419 uses the PSV resistor to set an inter-
nal timer that monitors the time between consecutive
high-side gate pulses. If the time exceeds the programmed
timer, DL drives high to turn the low-side MOSFET on. This
draws current from V OUT through the inductor, forcing both
V OUT and V FB to fall. When V FB drops to the 500mV thresh-
old, the next DH on-time is triggered. After the on-time is
completed the high-side MOSFET is turned off and the
low-side MOSFET turns on, and the internal timer is
restarted. The low-side MOSFET remains on until the
inductor current ramps down to zero, at which point the
low-side MOSFET is turned off. This ends the cycle until
V FB falls below the 500mV threshold, or the internal timer
forces another DL turn-on.
Because the period between on-times is limited to a
maximum value, a minimum operating frequency is main-
tained. Figure 5 shows ultrasonic power-save operation.
Power-Save Mode Operation
The device provides power-save operation at light loads
with no minimum operating frequency, selected by float-
ing the PSV pin (no connection). In this mode of opera-
tion, the internal zero crossing comparator monitors the
inductor current via the voltage across the low-side
MOSFET during the off-time. If the inductor current falls to
zero for 8 consecutive switching cycles, the controller
enters power-save operation. It will then turn off the low-
side MOSFET on each subsequent cycle, provided that the
current crosses zero. After the low-side MOSFET is off,
both high-side and low-sides MOSFETs remain off until V FB
drops to the 500mV threshold. While the MOSFETs are off
the load is supplied by the output capacitor. If the induc-
tor current does not reach zero on any switching cycle, the
controller immediately exits power-save and returns to
forced continuous mode. Figure 6 shows power-save
operation at light loads.
FB Ripple
Voltage (V FB )
Inductor
Current
minimum frequency
FB threshold
(500mV)
(0A)
FB Ripple
Voltage
(V FB )
Inductor
Current
Dead time varies
according to load
FB threshold
(500mV)
Zero (0A)
DH
DL
On-time
(T ON )
programmable time-out
DH On-time is triggered when
V FB reaches the FB Threshold
DH
DL
On-time (T ON )
DH On-time is triggered when
V FB reaches the FB Threshold.
After the programmable time-out, DL drives
high if V FB has not reached the FB threshold.
Figure 5 — Ultrasonic Power-Save Operation
DL drives high when on-time is completed.
DL remains high until inductor current reaches zero.
Figure 6 — Power-Save Operation
13
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