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參數(shù)資料
| 型號： | SC2441 |
| 廠商： | Semtech Corporation |
| 英文描述： | Very Low Input Voltage 2-Phase Synchronous Step-down Controllers with Step-up Converter |
| 中文描述： | 非常低的輸入電壓2相同步降壓與升壓轉(zhuǎn)換器控制器 |
| 文件頁數(shù)： | 11/35頁 |
| 文件大?。?/td> | 733K |
| 代理商： | SC2441 |
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11
2005 Semtech Corp.
www.semtech.com
POWER MANAGEMENT
Operation
SC2441
Overview
The SC2441 is a constant frequency triple-output
switching regulator especially designed for operating from
input voltages as low as 1.8V. It consists of two current-
mode step-down switch-mode PWM controllers driving
all N-channel MOSFET’s and a 1.7A step-up current-mode
controller with integrated 1.7A power switch. A low
voltage input (3.3V, 2.5V or 1.8V) can be stepped up to
5V-10V locally using the boost regulator to provide
sufficient gate drives for the step-down converters. The
boost converter can also be used to generate a third
output.
The two step-down channels of the SC2441 operate at
180 degrees out of phase from each other. Since input
currents are interleaved in a two-phase converter, input
ripple current is lower and smaller input capacitor can be
used for filtering.
The step-down controllers of the SC2441 operate in
synchronous continuous-conduction mode. They can be
configured either as two independent step-down
controllers producing two separate outputs or as a dual-
phase single-output controller by tying the FB2 pin to V
.
In single output operation, the channel-one error amplifier
controls both channels and the channel-two error
amplifier is disabled. Soft-start and overload hiccup of
both channels is also synchronized to channel one.
Frequency Setting and Synchronization
The step-up regulator in the SC2441 runs at twice the
frequency of step-down controllers. Each step-down
controller runs at one-half of the oscillator frequency and
is 180 degrees out of phase from the other step-down
controller. The switching frequency of the step-up
regulator is the oscillator frequency and can be set with
an external resistor from the R
pin to the ground. The
boost regulator and the step-down controllers are capable
of operating up to 2 MHz and 1 MHz respectively. It is
necessary to consider the operating duty-ratio range
before deciding the switching frequency. See Applications
Information section for more details.
When synchronized externally, the applied clock frequency
(hence switching frequency of the step-up converter)
should be twice the individual phase frequency of the
step-down controllers. The synchronizing clock frequency
should also be between 1-1.33 times the set free-running
frequency.
If not synchronized, the SYNC/SHDN pin should be tied
to the input. Pulling the SYNC/SHDN pin below 0.5V shuts
off the SC2441 after 85
μ
s time delay.
Control Loop
The step-down controllers and the boost regulator in the
SC2441 use peak current-mode control for fast transient
response, ease of compensation and current sharing in
single output operation. The low-side MOSFET of each
step-down channel is turned off at the falling-edge of
the phase clock. After a brief non-overlapping conduction
interval of 74ns, the high-side MOSFET is turned on. The
phase inductor current ramps up. When the sensed
inductor current reaches the threshold determined by
the error amplifier output and ramp compensation, the
high-side MOSFET is turned off. After a non-overlapping
delay of 62ns, the low-side MOSFET is turned on.
The supply voltages for the high-side gate drivers are
obtained from two diode-capacitor bootstrap circuits. If
the bootstrap capacitor is charged from V
, then the
high-side gate drive voltage will swing from approximately
2V
to the ground. The outputs of the low-side gate
drivers swing from V
CC
to the ground.
All three converters in the SC2441 have internal ramp-
compensation to prevent sub-harmonic oscillation when
operating above 50% duty cycle. The internal
compensating ramp is designed for an inductor ripple-
current of between to 1/3 of the maximum inductor
current and the peak-to-peak current-sense voltage (CSP-
CSN of the step-down controllers) of between to 1/3
of the current-limit threshold (50mV). The current-limits
of all three converters are unaffected by the
compensation ramps.
Current-Sensing
Since the inductor current ramp is used as the modulating
ramp in current-mode control, the inductor current needs
to be sensed. There are two current sensing methods for
the step-down controllers. Since the maximum current-
sense voltage (CSP-CSN) is only 50mV, a precision sense
resistor in series with the inductor can be used at the
output without resulting in excessive power dissipation.
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| SC2441EVB | Very Low Input Voltage 2-Phase Synchronous Step-down Controllers with Step-up Converter |
| SC2441ITSTRT | Very Low Input Voltage 2-Phase Synchronous Step-down Controllers with Step-up Converter |
| SC2442 | High Performance Wide Input Range Dual Synchronous Buck Controller |
| SC2442H | High Performance Wide Input Range Dual Synchronous Buck Controller |
| SC2442HITSTR | High Performance Wide Input Range Dual Synchronous Buck Controller |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| SC2441A | 制造商:SEMTECH 制造商全稱:Semtech Corporation 功能描述:1.8V to 20V Input 2-Phase Synchronous Step-down Controllers with Step-up Converter |
| SC2441A_09 | 制造商:SEMTECH 制造商全稱:Semtech Corporation 功能描述:1.8V to 20V Input 2-Phase Synchronous Step-down Controllers with Step-up Converter |
| SC2441AEVB | 制造商:SEMTECH 制造商全稱:Semtech Corporation 功能描述:1.8V to 20V Input 2-Phase Synchronous Step-down Controllers with Step-up Converter |
| SC2441ATETRT | 制造商:Semtech Corporation 功能描述: |
| SC2441EVB | 制造商:SEMTECH 制造商全稱:Semtech Corporation 功能描述:Very Low Input Voltage 2-Phase Synchronous Step-down Controllers with Step-up Converter |
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