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参数资料
| 型号： | SC189LSKTRT |
| 厂商： | Semtech |
| 文件页数： | 17/24页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK SYNC 1.8V SOT23-5 |
| 标准包装： | 1 |
| 类型： | 降压（降压） |
| 输出类型： | 固定 |
| 输出数： | 1 |
| 输出电压： | 1.8V |
| 输入电压： | 2.9 V ~ 5.5 V |
| PWM 型： | 电压模式 |
| 频率 - 开关： | 2.5MHz |
| 电流 - 输出： | 1.5A |
| 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： | SC-74A，SOT-753 |
| 包装： | 标准包装 |
| 供应商设备封装： | SOT-23-5 |
| 产品目录页面： | 1357 (CN2011-ZH PDF) |
| 其它名称： | SC189LSKDKR |
SC189
Maximum Power Dissiption T ? 125°C
Applications Information J (continued)
1500
1200
900
600
300
? JA = 90°C/W
SOT23-5 Package
the current limit holding current for the SC189 to exit
foldback current limit mode. Figure 5 shows the typical
current limit holding current decreasing rate over differ-
ent output voltage. The SC189 is capable of sustaining an
indefinite short circuit without damage and will resume
normal operation when the fault is removed. The foldback
current limit mode will be disabled during the soft-start.
package Output Current for T ? 125°C
0
-40 -25 -10 5 20 35 50 65 80 95 110 125
Ambient Temperature (°C)
Figure 2 — Maximum power dissiption of SOT23-5
over temperature
Maximum J
2.0
Over-Voltage Protection
In the event of a 15% over-voltage on the output, the
PWM drive is disabled with LX pin floating.
Soft-Start
1.8
1.6
1.4
1.2
1.0
V OUT =2.5V
V OUT =1.2V
The soft-start mode is activated after VIN reaches its
UVLO and EN signal is set high to enable the part. An over
temperature shutdown event will also activate the soft
start sequence. Soft-start mode controls the maximum
0.8
0.6
0.4
0.2
V IN = 5.0V
? JA = 90°C/W
V OUT = 3.3V
current during startup thus limiting in-rush current. The
PMOS current limit is stepped through four soft start
levels of approximately 20%, 25%, 40%, & 100%. Each
0.0
-40 -25 -10 5 20 35 50 65 80 95 110 125
Ambient Temperature (°C)
Figure 3 — Typical maximum output current over
for T ? 125°C of Output Current J
temperature Maximum SOT23-5 package, V IN = 5.0V
step is maintained for 20μs following internal reference
start up of 20μs giving the total nominal startup period
of 100μs. During startup, the chip operates in controlling
the inductor current swings between 0A and current
2.0
1.8
1.6
1.4
V OUT =1.2V
limit. If V OUT reaches 90% of the target within the first 2
current levels, the chip continues in hysteretic mode till
the end of the soft-start time period before switching to
1.2
1.0
0.8
0.6
0.4
0.2
V IN = 3.3V
? JA = 90°C/W
V OUT =2.5V
PWM mode. If V OUT does not reach 90% by the end of the
second current limit level, soft start will continue to level 3
or level 4 till the output voltage reaches 96% and will then
transition into PWM mode. After the full soft start time
period, the SC189 will switch into PWM mode operation
0.0
-40 -25 -10 5 20 35 50 65 80 95 110 125
Ambient Temperature (°C)
Figure 4 — Typical maximum output current over
temperature of SOT23-5 package, V IN = 3.3V
Current Limit Holding Current over Vout
regardless of the V OUT level.
The SC189 is capable of starting up into a pre-biased
output. When the output is precharged by another supply
150
120
90
60
30
0
T A = 25°C
V IN = 3.6V
V IN = 5.0V
rail, the SC189 will not discharge the output during the
soft start interval.
Shut Down
When the EN pin voltage goes low, the SC189 will run in
shutdown mode, drawing less than 1μA from the input
power supply. The internal switches and bandgap voltage
will be immediately turned off.
1.0
1.5
2.0
2.5
3.0
3.5
Output Voltage (V)
Figure 5 — Current limit holding current decreasing
rate vs. output voltage
Inductor Selection
The SC189 converter has internal loop compensation. The
? 2009 Semtech Corp.
17
www.semtech.com
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