参数资料
| 型号： | SC493ULTRT |
| 厂商： | Semtech |
| 文件页数： | 16/28页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM MLPQ-20 |
| 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 ~ 5.5 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： | SC493ULTRTDKR |
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SC493
Applications Information (continued)
Dynamic Output Voltage Control
SC493 allows changing the output voltage when the part
is already switching. Whenever the output voltage is
changed via margining or by fine adjust, the controller
changes the internal reference by small intermediate steps
using 32us per step. This ensures that the output keeps up
with internal slewing and excessive current does not build
up in the inductor. The faults are blanked till the end of the
slewing. Blanking is released when 8 switching cycles
occur after the end of internal slewing since the switching
cycles indicate that the part is in regulation. The part is
enabled to operate in DCM mode to prevent negative
current build up in the inductor when slewing down. The
part returns to the previous operational state (DCM or
CCM) at the end of blanking.
Since the controller operates in DCM, it depends on the
load to discharge the output when slewing down. Therefore,
no switching cycles may occur if the load is very light and
the output will not keep pace with the internal slew. In such
cases, the blanking at the end of slewing will end after a
1ms timeout whether any switching cycles occur or not and
the part will return to its previous operational state.
For applications that need to have the output slew down at
the same rate as the internal slewing, register bit Enable
Internal Load (EnIntLd) can be set. This activates an internal
10? pull down on Vout when the part is slewing down. This
resistance discharges the output capacitor and helps the
output keep pace with internal slewing. To help maximize
efficiency, the pulldown will not activate when slewing up
even if the feature is enabled via register settings.
When the internal pull down is enabled, it is active only for
the time it takes the internal reference to reach its target.
For example, when slewing from VFBadjust of +9% to 0%,
the pull down is active only for 12 x 32μs = 384μs. In appli-
cations with large output capacitors, this time may not be
sufficient to discharge the output to keep up with the
internal reference. Therefore, the output can be higher
than the desired regulation value at the end of the slewing
sequence. If the part was in DCM before slewing began,
abled or set to ultrasonic before the output is slewed. This
will ensure that the low side MOSFET will turn back on at
the end of the slewing sequence even if there is no load
and bring the output voltage back into regulation. Figure
4 demonstrates this with a 1000μF output capacitor and
with psave disabled before slewing from VFBadj = +9% to
VFBadj = -9%.
SCL (5V/div)
V OUT (100mV/div)
PGOOD (5V/div)
Time (500μs/div)
Figure 4 — Slew Down in CCM with Large Output
Capacitors
Soft-shutdown
SC493 features a soft-shutdown feature: whenever switch-
ing is disabled, an internal 10? pull-down activates on the
Vout pin which discharges the output capacitor and holds
Vout low. The pull-down stays active even if the EN pin is
subsequently driven low. Note that the pull-down will not
activate if EN pin has not been high after power has been
applied or power is cycled with EN pin low.
SmartDrive TM
For each DH pulse, the DH driver initially turns on the
high-side MOSFET at a slower speed, allowing a softer,
smooth turn-off of the low-side diode. Once the diode is
off and the LX voltage has risen 0.5V above PGND, the
SmartDrive circuit automatically drives the high-side
MOSFET on at a rapid rate. This technique reduces switch-
ing noise while maintaining high efficiency, reducing the
need for snubbers or series resistors in the gate drive.
the output will stay at the higher value at the end of the
sequence. If there is no load, the output will return to the
desired value very slowly. In such applications, to ensure
that the controller quickly brings the output voltage into
regulation, it is recommended that either PSAVE be dis-
16
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