参数资料
| 型号： | SC493ULTRT |
| 厂商： | Semtech |
| 文件页数： | 13/28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)
latch off just because this bit is set. The PGD output is
driven low when the FB pin is above 120% of the nominal
voltage and returns to high when the FB pin is below 110%
of the nominal voltage.
Output Over Current Protection
The SC493 features adjustable current limit capability.
The R DS(ON) of the external low side MOSFET is used as the
current sensing element. The over current limit is set by
R ILIM (connected externally). Internally there is a 10μA
current source that feeds the ILIM pin when the low side
MOSFET has turned on. This current flows through the R ILIM
resistor and creates a voltage drop across it. When the low
side MOSFET turns on, the inductor current flowing
through it creats a voltage across the MOSFET due to its
R DS(ON) . If this voltage drop exceeds the voltage across the
R ILIM resistor, current limit will activate. This prevents the
high side MOSFET from turning on until the voltage drop
across the low side MOSFET falls below the voltage across
the R ILIM resistor. This effectively sets a valley current limit
of R ILIM x 10μA/R DS(ON) . Please note that R DS(ON) of the MOSFET
is dependent on the V GS voltage (equals to PVDD applied
to SC493). The ILIM flag bit is set whenever current limit
occurs. The converter does not latch off just because this
bit is set.
Output Under Voltage Protection
The output under voltage condition occurs with or without
current limit. The output under voltage without current
Over Temperature Protection
When the temperature of the device reaches the over
temperature rising threshold, the OT flag bit is set, turning
off both high side and low side MOSFETs. After the
temperature of the device drops to the over temperature
falling threshold, the converter restarts as if the device
has been enabled. The converter will go through power-
on delay and soft start.
Synchronous Buck Converter Operation, Ben-
efits, and Features
The SC493 employs pseudo-fixed frequency adaptive on-
time control. This control method allows fast transient
response thereby lowering the size of the power
components needed in the system.
The on time is determined by an internal one-shot with a
period proportional to the output voltage and inversely
proportional to the input voltage. The output ripple
voltage generated by the ESR of the output capacitance is
used as the PWM ramp signal. This ripple voltage
determines the off time for the controller.
For the SC493 the operating frequency range is from 250kHz
to 1MHz , programmable via the I 2 C interface.
Adaptive on-time control has significant advantages over
traditional control methods. Some of the advantages of
the adaptive on-time control are:
limit is normally a result of low input voltage. The control-
ler will look at the inductor current to differentiate these
two situations and respond accordingly. After PGD is
asserted, if the FB voltage falls below the PGD falling
threshold (80%) and current limit does not happen simul-
taneously, the Brown Out (BO) flag bit is set. This indicates
an output under voltage has happened because of low
input voltage. The converter does not latch off just
because the BO bit is set. After PGD is asserted, if FB
?
?
?
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No error amplifier, which reduces external com-
ponents used for compensation
Predictable frequency spread because of adap-
tive on-time architecture
Fast transient response — operation with
minimum output capacitance
Overall superior performance compared to fixed
frequency architectures
voltage falls below 70% of the nominal voltage for 8 con-
secutive current limited switching cycles, the UVO flag bit
is set. This latches the converter off, with both the high
side and low side MOSFETs turned off.
To restart, either the EN pin or ENSW register bit must be
set low and then back to high.
On-Time One-Shot Generator (TON)
Adaptive on-time controllers like the SC493 have an
internal on-time one-shot generator. The one-shot timer
uses an internal comparator and a capacitor. The positive
input of the comparator is a voltage proportional to the
output voltage and the negative input is connected to the
capacitor charged by a current proportional to the input
voltage. The TON time is the time required to charge this
13
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