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參數(shù)資料
| 型號： | SC2441AEVB |
| 廠商： | Semtech Corporation |
| 英文描述： | 1.8V to 20V Input 2-Phase Synchronous Step-down Controllers with Step-up Converter |
| 中文描述： | 1.8V至20V的輸入2相同步降壓與升壓轉換器控制器 |
| 文件頁數(shù)： | 19/37頁 |
| 文件大?。?/td> | 1024K |
| 代理商： | SC2441AEVB |
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19
2006 Semtech Corp.
www.semtech.com
POWER MANAGEMENT
Operation (Cont.)
SC2441A
In closed loop operation, EA1 and EA2 output voltage
vary from 1.2V to 3.5V with the range 1.2V to 1.85V
corresponding to negative peak sense voltages. Both gate
drives are kept off until the COMP voltage exceeds 1.85V
in start up.
The error amplifier of the step-up converter has a 1.25V
reference voltage. Its output voltage excursion is from 0.8V
to 1V in closed-loop operation.
Current-Limit
The 25mV maximum current sense voltage is the cycle-by-
cycle peak current limit of the step-down controller.
Gate Drivers
The SC2441A uses an adaptive non-overlapping control
scheme to switch the upper and the synchronous
MOSFETs. The synchronous MOSFET of each step-down
channel is turned off at the falling-edge of the phase
clock. The control (upper) MOSFET is not turned on until
the synchronous gate drive goes low. The phase inductor
current ramps up. When the sensed inductor current
reaches the threshold determined by the error amplifier
output and ramp compensation, the control MOSFET is
turned off. The synchronous MOSFET is not turned on
until the upper gate drive goes low.
The supply voltage for the upper gate driver is obtained
from a diode-capacitor bootstrap circuit. If the bootstrap
capacitor is charged from V
, then the high-side gate drive
voltage will swing from approximately 2V
to ground. The
synchronous gate drive swings from V
CC
to ground.
Soft-Start and Overload Protection
Figure 4 shows the functional diagram of the soft-start
and overload protection circuit. The soft-start capacitor
C
and its charging resistor R
are tied to the SS/EN pin.
Together they set the soft-start time. Before V
rises to
4.5V, the undervoltage lockout circuit discharges C
SS
to
ground. After V
rises above 4.5V, Q
1
turns off and C
is
slowly charged by R
. Comparator C
and latch L
first
disable both the upper and lower gate drives. Hysteretic
comparator C
1
resets the latch L
1
so that hiccup is disabled
during start up. As mentioned above, there is no PWM
(=TGON) pulse until C
is above 1.25V and the
corresponding COMP rises above 1.85V. Once the first
TGON pulse appears, L
is reset and both gate drivers of
that channel are enabled.
After C
is charged above 3.3V, C
output goes low.
Hiccup is armed. If the output voltage is less than 70%
of the set value due to improper start up or output
overload, then C
will set the overload latch L
. Both gate
drivers of the channel are turned off and the 10
μ
A
current source discharges C
. R
must be large enough
to ensure full discharge of C
down to 0.5V. Soft-start
process should be slow enough to allow the output to
reach 70% of its final value before hiccup is armed. The
overload latch L
is reset when the C
capacitor is
discharged below 0.5V. The 10
μ
A current source turns
off. C
capacitor is recharged by R
and the converter
undergoes soft-start. If overload persists, the step-down
converters will undergo repetitive shutdown and restart
(hiccup).
If the output is short-circuited, the inductor current will
not increase indefinitely between the times the inductor
current reaching its current limit and shutdown. This is
due to cycle skipping reduces the actual operating
frequency.
Pulling the SS/EN pin below 0.8V with an open-collector
transistor sets the disable latch L
and turns off the gate
drives. The SS/EN pin can be used as the enable input for
the controller.
The soft start timing diagram and the hiccup operation
timing diagram are shown in Figures 6a and 6b
respectively.
相關PDF資料 |
PDF描述 |
|---|---|
| SC2441ATETRT | 1.8V to 20V Input 2-Phase Synchronous Step-down Controllers with Step-up Converter |
| SC2441 | Very Low Input Voltage 2-Phase Synchronous Step-down Controllers with Step-up Converter |
| 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 |
相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| 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 |
| SC2441ITSTRT | 制造商:Semtech Corporation 功能描述:Controller IC |
| SC2442 | 制造商:SEMTECH 制造商全稱:Semtech Corporation 功能描述:High Performance Wide Input Range Dual Synchronous Buck Controller |
| SC2442H | 制造商:SEMTECH 制造商全稱:Semtech Corporation 功能描述:High Performance Wide Input Range Dual Synchronous Buck Controller |
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