参数资料
| 型号： | SC198AMLTRT |
| 厂商： | Semtech |
| 文件页数： | 11/15页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK SYNC PROG .8A 20MLPQ |
| 标准包装： | 1 |
| 类型： | 降压（降压） |
| 输出类型： | 可调式 |
| 输出数： | 2 |
| 输出电压： | 可编程 |
| 输入电压： | 2.7 V ~ 5.5 V |
| 频率 - 开关： | 1MHz |
| 电流 - 输出： | 800mA |
| 同步整流器： | 是 |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 20-MLPQ |
| 包装： | 标准包装 |
| 供应商设备封装： | 20-MLPQ（4x4） |
| 其它名称： | SC198AMLDKR |
NOT RECOMMENDED FOR NEW DESIGN
Application Information (continued)
SC198A
In PSAVE mode (see Figure 1), VOUT regulation is con-
trolled by bursts in switching. While the output voltage is
Protection Features
The SC198A provides the following protection features:
between the low and high voltage thresholds, switching
is stopped to reduce loss. When the voltage drops to the
lower threshold, the switch bursts at a fixed on time until
the upper threshold is reached. At this point the output
voltage is allowed to ramp down to the lower threshold
without switching to conserve power. In the PSAVE mode,
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Thermal Shutdown
Current Limit
Over-Voltage Protection
Soft-Start
less switching is used. This results in less power loss which
can be seen in the difference of effi ciency between PWM
mode and PSAVE mode at light loads.
Thermal Shutdown
The SC198A has a thermal shutdown feature to protect
against damage if the junction temperature exceeds
145°C. In thermal shutdown, the on-chip power devices
PSAVE Mode at
Higher Load
Applied
PSAVE Mode at
PWM Mode at
are disabled, tri-stating the LX output. Switching resumes
Upper
Thershold
Limit
Lower
Thershold
Moderate Load
BURST OFF BURST
OFF
High Load
BURST
High Load
PWM Mode
when the temperature drops by 10°C. During this time, if
the output voltage decreases by more than 60% of its
programmed value, a soft-start will be invoked.
Limit
V OUT
PSAVE
Exit
Threshold
Inductor
Current
Current Limit
The internal power devices are protected by current limit
functions. In the event of a short to ground on the output,
the part enters frequency foldback mode. This causes the
switching frequency to decrease by a factor determined
by the output voltage. This prevents the inductor current
from staircasing.
Over-Voltage Protection
0A
Time
Figure 1 — PSAVE Operation
In the event of an over-voltage on the output in switcher
mode, the PWM drive is disabled, effectively tri-stating
the LX output. The part will not resume switching until
The PSAVE switching burst frequency is controlled such
that the inductor current ripple during the burst is similar
the output voltage has fallen below 2% of the regulation
voltage.
to that in PWM mode.
Soft-Start
The SC198A automatically detects when to exit PSAVE
mode. The device sets a maximum peak current in PSAVE
mode, and then detects when VOUT falls due to the load
increasing above the level that the peak current will
support.
For the SC198A to exit PSAVE mode, the load must be
increased, which causes VOUT to decrease until the PSAVE
The soft-start mode operates by limiting the current
through the inductor and controlling the switching fre-
quency. The current limit is increased over several
milliseconds in discrete steps. This has the desired effect
of limiting in-rush current from the input supply. The soft-
start mode is cancelled once the output reaches
regulation. Soft-start is only re-enabled by power cycling,
toggling enable, a UVLO event, or shutdown.
exit threshold is reached. PSAVE levels are set high to
minimize the undershoot when the SC198A exits PSAVE.
Figure 1 shows PSAVE mode operation and exiting into
PWM mode at increased load.
11
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