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參數(shù)資料
| 型號： | SC411EVB |
| 廠商： | Semtech Corporation |
| 英文描述： | Synchronous Buck Pseudo-Fixed Frequency Power Supply Controller |
| 中文描述： | 同步降壓偽固定頻率電源控制器 |
| 文件頁數(shù)： | 11/27頁 |
| 文件大?。?/td> | 488K |
| 代理商： | SC411EVB |
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11
2007 Semtech Corp.
www.semtech.com
SC411
POWER MANAGEMENT
Application Information (Cont.)
The current limit circuitry also protects against negative
over-current (i.e. when the current is
fl
owing from the load
to PGND through the inductor and bottom MOSFET). In
this case, when the bottom MOSFET is turned on, the
phase node, LX, will be higher than PGND initially. The
SC411 monitors the voltage at LX, and if it is greater than
a set threshold voltage of 125mV (nom) the bottom MOS-
FET is turned off. The device then waits for approximately
2.5
μ
s and then DL goes high for 300ns (typ) once more
to sense the current. This repeats until either the over-
current condition goes away or the part latches off due to
output over-voltage (see Output Over-voltage Protection).
Power Good Output
The power good output is an open-drain output and re-
quires a pull-up resistor.
When the output voltage is 16%
above or 10% below its set voltage, PGD gets pulled low. It
is held low until the output voltage returns to within these
tolerances once more.
PGD is also held low during start-
up and will not be allowed to transition high until soft start
is over (440 switching cycles) and the output reaches 90%
of its set voltage. There is a 5
μ
s delay built into the PGD
circuitry to prevent false transitions.
Output Over-Voltage Protection
When the output exceeds 16% of the its set voltage the
low-side MOSFET is latched on. It stays latched on and
the controller is latched off until reset*. There is a 5
μ
s
delay built into the OV protection circuit to prevent false
transitions.
Output Under-Voltage Protection
When the output is 30% below its set voltage the output
is latched in a tri-stated condition. It stays latched and
the controller is latched off until reset*. There is a 5
μ
s
delay built into the UV protection circuit to prevent false
transitions.
POR, UVLO and Soft-Start
An internal power-on reset (POR) occurs when VCCA ex-
ceeds 3V, starting up the internal biasing. VCCA under-
voltage lockout (UVLO) circuitry inhibits the controller until
VCCA rises above 4.2V. At this time the UVLO circuitry
resets the fault latch and soft-start counter, and allows
switching to occur if the device is enabled. Switching al-
ways starts with DL to charge up the BST capacitor. With
the soft-start circuit (automatically) enabled, it will pro-
gressively limit the output current (by limiting the current
out of the ILIM pin) over a predetermined time period of
440 switching cycles.
The ramp occurs in four steps:
1) 110 cycles at 25% ILIM with double minimum off-time
(for purposes of the on-time one-shot, there is an internal
positive offset of 120mV to VOUT during this period to aid
in startup).
2) 110 cycles at 50% ILIM with normal minimum off-
time.
3) 110 cycles at 75% ILIM with normal minimum off-time.
4) 110 cycles at 100% ILIM with normal minimum off-
time.
At this point the output under-voltage and power good cir-
cuitry is enabled.
There is 100mV of hysteresis built into the UVLO circuit
and when VCCA falls to 4.1V (nom) the output drivers are
shut down and tri-stated.
MOSFET Gate Drivers
The DH and DL drivers are optimized for driving moder-
ate-sized high-side, and larger low-side power MOSFETs.
An adaptive dead-time circuit monitors the DL output and
prevents the high-side MOSFET from turning on until DL is
fully off (below ~1V). Semtech’s SmartDriver
TM
FET drive
fi
rst pulls DH high with a pull-up resistance of 10
Ω
(typ)
until LX = 1.5V (typ). At this point, an additional pull-up
device is activated, reducing the resistance to 2
Ω
(typ);
This negates the need for an external gate or boost re-
sistor. The adaptive dead time circuit also monitors the
phase node, LX, to determine the state of the high side
MOSFET, and prevents the low side MOSFET from turning
on until DH is fully off (LX below ~1V). Be sure there is
low resistance and low inductance between the DH and
DL outputs to the gate of each MOSFET.
* Note: to reset from any fault, VCCA or EN/PSV must be toggled.
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相關(guān)代理商/技術(shù)參數(shù) |
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| SC411MLTRT | 制造商:Semtech Corporation 功能描述:Synchronous Buck Pseudo-Fixed Frequency Power Supply Controller |
| SC412A | 制造商:SEMTECH 制造商全稱:Semtech Corporation 功能描述:Synchronous Buck Controller |
| SC412A_1 | 制造商:SEMTECH 制造商全稱:Semtech Corporation 功能描述:Synchronous Buck Controller |
| SC412AEVB | 制造商:SEMTECH 制造商全稱:Semtech Corporation 功能描述:Synchronous Buck Controller |
| SC412AMLTRT | 功能描述:IC REG CTRLR BUCK PWM 16-MLP RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標(biāo)準(zhǔn)包裝:4,000 系列:- PWM 型:電壓模式 輸出數(shù):1 頻率 - 最大:1.5MHz 占空比:66.7% 電源電壓:4.75 V ~ 5.25 V 降壓:是 升壓:無 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 工作溫度:-40°C ~ 85°C 封裝/外殼:40-VFQFN 裸露焊盤 包裝:帶卷 (TR) |
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