参数资料
| 型号： | SC419ULTRT |
| 厂商： | Semtech |
| 文件页数： | 12/24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)
This method automatically produces an on-time that is
proportional to V OUT and inversely proportional to V IN .
Under steady-state conditions, the switching frequency
V OUT
0 . 5
1
R 1
R 2
V RIPPLE
2
f SW
R TON
can be determined from the on-time by the following
equation.
V OUT
T ON V IN
The SC419 uses an external resistor to set the on-time
which indirectly sets the frequency. The on-time can be
programmed to provide an operating frequency from
200kHz to 1MHz using a resistor between the TON pin and
ground. The resistor value is selected by the following
equation.
( T ON 10ns ) V IN
25 pF V OUT
Forced Continuous Mode Operation
The SC419 operates in FCM (Forced Continuous Mode) by
connecting the PSV pin to VDDA. (The PSV pin should not
exceed the VDDA supply.) See Figure 4 for FCM waveforms.
In this mode one of the power MOSFETs is always on, with
no intentional dead time other than to avoid cross-con-
duction. This results in uniform frequency across the full
load range with the trade-off being reduced efficiency at
light loads due to the high-frequency switching of the
MOSFETs.
FB Ripple
Voltage (V FB ) FB threshold
(500mV)
The maximum R TON value allowed is shown by the follow-
ing equation.
V IN _ MIN
R TON _ MAX
15 A
Immediately after the on-time, the DL output drives high
to energize the low-side MOSFET. DL has a minimum high
time of ~250ns, after which DL continues to stay high until
one of the following occurs:
Inductor
Current
DH
On-time
(T ON )
DC Load Current
DH on-time is triggered when
V FB reaches the FB Threshold.
?
?
VFB falls below the 500mV reference
The Zero Cross Detector trips if power-save is
active
DL
DL drives high when on-time is completed.
DL remains high until V FB falls to the FB threshold.
V OUT Voltage Selection
The output voltage is regulated by comparing V OUT as seen
through a resistor divider at the FB pin to the internal
500mV reference (see Figure 3).
Figure 4 — Forced Continuous Mode Operation
The switcher output voltage can be programmed higher
than 5V with careful design. In this case the VOUT pin
cannot connect directly to the switcher output due to its
the maximum voltage rating. An additional resistor
V OUT
R 1
R 2
To FB pin
divider network is required to connect from the switcher
output to the VOUT pin. The voltage at the VOUT pin
should be at least 500mV lower than the VDDA supply, to
prevent the VLDO switch-over function. For example, the
voltage at the VOUT pin can be 4V if VDDA is set for 5V.
Figure 3 — Output Voltage Selection
Note that this control method regulates the valley of the
output ripple voltage, not the DC value. The DC value of
V OUT is offset by the output ripple according to the follow-
ing equation.
When the SC418 operates from an external power source
and the LDO is disabled by grounding the ENL pin, the
voltage at the VOUT pin can be as high as shown in
Recommended Operating Conditions. Note that RTON
must be adjusted higher by the same divider ratio to
12
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