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参数资料
| 型号： | SC185QULTRT |
| 厂商： | Semtech |
| 文件页数： | 14/18页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK SYNC 3.3V 4A 16MLPQ |
| 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： | 3.3V |
| 输入电压： | 2.9 V ~ 5.5 V |
| PWM 型： | 电压模式 |
| 频率 - 开关： | 1.5MHz |
| 电流 - 输出： | 4A |
| 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： | 16-UFQFN 裸露焊盘 |
| 包装： | 标准包装 |
| 供应商设备封装： | 16-MLPQ-UT（3x3） |
| 其它名称： | SC185QULDKR |
SC185
Applications Information (continued)
Current Limit & OCP
The internal PMOS power device in the switching stage is
protected by a current limit feature. If the inductor current
is above the PMOS current limit for 16 consecutive cycles,
the part enters foldback current limit mode and the output
current is limited to the current limit holding current
(I CL_HOLD ) which is approximately 900mA. Under this condi-
tion, the output voltage will be the product of I CL_HOLD and
the load resistance. When the load presented falls below
the current limit holding level, the output will charge to
the upper PSAVE voltage threshold and return to normal
operation. The SC185 is capable of sustaining an indefi-
nite short circuit without damage. During the soft start, if
current limit has occurred before the SS voltage has
reached 400mV, the part enters foldback current limit
mode. Foldback current limit mode will be disabled during
soft-start after the SS voltage is higher than 400mV.
Over-Voltage Protection
In the event of a 15% over-voltage on the output, the
PWM drive is disabled with the LX pin floating. Switching
does not resume until the output voltage falls below the
nominal Vout regulation voltage.
Soft-Start
The soft-start mode is activated after AVIN reaches it ’s
UVLO voltage threshold and EN is set high to enable the
part. A thermal shutdown event will also activate the soft
start sequence. The Soft-start mode controls the slew-rate
of the output voltage during startup thus limiting in-rush
current on the input supply. During start up, the reference
voltage for the error amplifier is clamped by the voltage
on SS pin. The output voltage slew rate during soft start is
determined by the value of the external capacitor con-
nected to the SS pin and the internal 5μA charging current.
The SC185 requires a minimum soft-start time from enable
to final regulation in the order of 200μs, including the
50μs enable delay. As a result the soft start capacitor, Css,
should be higher than 1.5nF. During start up, the chip
operates in forced PWM mode. The value of Css for the
desired soft-start time, tss, can be determined by Equation
1.
output. When the output is pre-charged by another
supply rail, the SC185 will not discharge the output during
the soft start period.
Shut Down
When the EN pin is low, the SC185 will run in shutdown
mode, drawing less than 1μA (typ.) from the input power
supply. The internal switches and bandgap voltage will be
immediately turned off.
Thermal Shutdown
The device has a thermal shutdown feature to protect
the SC185 if the junction temperature exceeds 160°C.
During thermal shutdown, the on-chip power devices are
disabled, floating the LX output. When the temperature
drops by 10°C, it will initial a soft start cycle to resume
normal operation.
Under-Voltage Lockout
Under-Voltage Lockout (UVLO) is enabled when the
input voltage drops below the UVLO threshold. This
prevents the device from entering an ambiguous state
in which regulation cannot be maintained. Hysteresis of
approximately 300mV is included to prevent chattering
near the threshold. When the AVIN voltage reaches back
to the turn-on threshold and EN is high, the soft-start
mode is resumed.
Power Good
The power good (PGOOD) is an open-drain output. When
the output voltage drops below 10% of nominal voltage,
the PGOOD pin is pulled low after a 20μs delay. During
start-up, PGOOD will be asserted 1.8ms (typ.) after the
output voltage reaches 90% of the final regulation
voltage. The faults of over voltage, fold-back current limit
mode and thermal shutdown will force PGOOD low after
a 20 μ s delay. When recovering from a fault, PGOOD will be
asserted 1.8ms (typ.) after Vout reaches 90% of the final
regulation voltage.
Enable
The EN input is used to enable or disable the device when
t SS = C SS ×
0 . 5 V
5 μ A
(1)
the device is not in UVLO. When EN is low (grounded), the
device enters shutdown mode and consumes less than
1μA of current. In shutdown mode, the device tri-states
The SC185 is capable of starting up into a pre-biased
the LX pin and pulls down the SS pin. The EN pin has a
500kΩ internal pull-down resistor. This resistor is switched
? 2010 Semtech Corp.
14
www.semtech.com
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