参数资料
| 型号： | SC2443MLTRT |
| 厂商： | Semtech |
| 文件页数： | 12/22页 |
| 文件大小： | 0K |
| 描述： | IC DUAL SYNC STP-DN CTRLR 24MLPQ |
| 标准包装： | 1 |
| 应用： | 控制器，DDR |
| 输入电压： | 4.75 V ~ 16 V |
| 输出数： | 2 |
| 输出电压： | 可调至 0.5V |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 24-MLPQ |
| 供应商设备封装： | 24-MLPQ（4x4） |
| 包装： | 标准包装 |
| 产品目录页面： | 1358 (CN2011-ZH PDF) |
| 其它名称： | SC2443MLDKR |
SC2443
Applications Information (continued)
The non-inverting input of the first feedback amplifier is
tied to the internal 0.5V voltage reference. Both the non-
inverting and the inverting inputs of the second error
amplifier are brought out as device pins so that the output
of the second converter can be made to track the output
of the first channel. For example in DDR applications,
Channel can be used to generate VDDQ (2.5V) from
the input (5V or 2V) and channel 2 is used to produce a
tracking VTT ( .25V) with VDDQ being its input.
Current-Limit
The maximum current sense voltage of +75mV is the
cycle-by-cycle peak current limit when the load is
drawing current from the converter. There is no cycle-by-
cycle current limiting when the inductor current flows in
the negative direction. However once the valley of the
current sense voltage exceeds - 0mV, the corresponding
channel will undergo shutdown and restart (hiccup).
Soft-Start and Overload Protection
The undervoltage lockout circuit discharges the SS/EN
capacitors. After VCC rises above 4.5V, the SS/EN capacitors
are slowly charged by internal 2 m A current source. With
internal PNP transistors, the SS/EN voltages clamp the error
amplifier outputs. When the error amplifier output rises
to 2.2V, the high-side MOSFET starts to switch. As the SS/
EN capacitor continues to be charged, the COMP voltage
follows. The converter gradually delivers increasing power
to the output. The inductor current follows the COMP
voltage envelope until the output goes into regulation.
The SS/EN clamp on COMP is then released.
After the SS/EN capacitor is charged above 3.2V (high
enough for the error amplifier to provide full load current),
the overload detection circuit is activated. If the output
voltage falls below 70% of its set value or the valley
current-sense voltage exceeds - 0mV, an overload latch
will be set and both the top and the bottom MOSFETs will
be turned off. The SS/EN capacitor is slowly discharged
with an internal .4 m A current sink. The overload latch
is reset when the SS/EN capacitor is discharged below
0.5V. The SS/EN capacitor is then recharged with the 2uA
current source and the converter undergoes soft-start.
If overload persists, the SC2443 will undergo repetitive
shutdown and restart.
If the output is short-circuited, the inductor current will
not increase indefinitely between the time the inductor
current reaching its current limit and the instant the
converter shuts down. This is due to cycle skipping(a
consequence of inductor current sense) reduces the
actual operating frequency.
The SS/EN pin can also be used as the enable input for that
channel. Both the high-side and the low-side MOSFETs
will be turned off if the SS/EN pin is pulled below 0.7V.
Operating Frequency (fs)
The switching frequency in the SC2443 is user-
programmable. The advantages of using constant
frequency operation are simple passive component
selection and ease of feedback compensation. Before
setting the operating frequency, the following trade-offs
should be considered.
) Passive component size
2) Circuitry efficiency
3) EMI condition
4) Minimum switch on time and
5) Maximum duty ratio
For a given output power, the sizes of the passive
components are inversely proportional to the switching
frequency, whereas MOSFET and Diodes switching losses
are proportional to the operating frequency. Other
issues such as heat dissipation, packaging and the cost
issues are also to be considered. The frequency bands
for signal transmission should be avoided because of EM
interference.
Minimum Switch On Time Consideration
In the SC2443 the falling edge of the clock turns on the
top MOSFET. The inductor current and the sensed voltage
ramp up. After the sensed voltage crosses a threshold
determined by the error amplifier output, the top MOSFET
is turned off. The propagation delay time from the turn-
on of the controlling FET to its turn-off is the minimum
switch on time. The SC2443 has a minimum on time of
about 50ns at room temperature. This is the shortest on
interval of the controlling FET. The controller either does
not turn on the top MOSFET at all or turns it on for at least
50ns.
For a synchronous step-down converter, the operating
duty cycle is VO / VIN . So the required on time for the
top MOSFET is VO / ( VIN × F S ) . If the frequency is set
such that the required pulse width is less than 50ns,
then the converter will start skipping cycles. Due to
minimum on time limitation, simultaneously operating at
2
相关PDF资料 |
PDF描述 |
|---|---|
| SC2446ITETRT | IC SYNC STEP DOWN CTRLR 28-TSSOP |
| SC2544TSTRT | IC REG CTRLR BUCK PWM VM 24TSSOP |
| SC2595MLTRT | IC DDR TERMINATION REG 16-MLPQ |
| SC2596STRT | IC INTEGRTD DDRII TERM REG 8SOIC |
| SC2608BSTRT | IC REG CTRLR BUCK PWM VM 8-SOIC |
相关代理商/技术参数 |
参数描述 |
|---|---|
| SC2446 | 制造商:SEMTECH 制造商全称:Semtech Corporation 功能描述:Dual-Phase Single or Two Output Synchronous Step-Down Controllers |
| SC2446A | 制造商:SEMTECH 制造商全称:Semtech Corporation 功能描述:Dual-Phase, Single or Dual Output Synchronous Step-Down Controller |
| SC2446AEVB | 制造商:SEMTECH 制造商全称:Semtech Corporation 功能描述:Dual-Phase, Single or Dual Output Synchronous Step-Down Controller |
| SC2446AITSTRT | 制造商:SEMTECH 制造商全称:Semtech Corporation 功能描述:Dual-Phase, Single or Dual Output Synchronous Step-Down Controller |
| SC2446EVB | 制造商:SEMTECH 制造商全称:Semtech Corporation 功能描述:Dual-Phase Single or Two Output Synchronous Step-Down Controllers |
发布紧急采购，3分钟左右您将得到回复。