- 您現(xiàn)在的位置：買賣IC網(wǎng) > PDF目錄374713 > SC1218 (Semtech Corporation) High Speed Synchronous MOSFET Driver PDF資料下載
參數(shù)資料
| 型號： | SC1218 |
| 廠商： | Semtech Corporation |
| 英文描述： | High Speed Synchronous MOSFET Driver |
| 中文描述： | 高速同步MOSFET驅(qū)動器 |
| 文件頁數(shù)： | 9/12頁 |
| 文件大小： | 356K |
| 代理商： | SC1218 |
9
2005 Semtech Corp.
www.semtech.com
POWER MANAGEMENT
Applications Information
THEORY OF OPERATION
The SC1218 is a high speed, robust, dual output driver
designed to drive top and bottom MOSFETs in a synchro-
nous Buck converter. It features internal bootstrap diode,
adaptive delay for shoot-through protection, 12V gate drive
voltage, and disable shutdown. It also supports dynamic
VID operation and CROWBAR function. This driver com-
bined with PWM controller SC2649 forms a multi-phase
voltage regulator for advanced microprocessors.
SC1218
Startup and UVLO
To startup the driver, a supply voltage is applied to the VIN
pin of the SC1218. The top and bottom gates are held
low until VIN exceeds the UVLO threshold of the driver,
typically 4.0V. The UVLO threshold has hysteresis, typi-
cally -250mV, to improve the nosie immunity from the VIN
pin.
Gate Transition and Shoot-through Protection
Refer to the Timing Diagrams section, the rising edge of
the PWM input initiates the turn-off of bottom FET and the
turn-on of top FET. After a short propagation delay (t
)
from PWM rising edge, the bottom gate falls (t
). The
adaptive circuit in the SC1218 detects the bottom gate
voltage. It holds the top gate off until the bottom gate
voltage drops below 1.4V for a preset delay time (t
).
This prevents the top FET from turning on until the bottom
FET is off. During the transition, the inductor current is
freewheeling through the body diode of either bottom FET
or top FET, depended on the direction of the inductor cur-
rent. The phase node could be low (ground) or high (V
IN
).
The falling edge of the PWM input controls the turn-off of
top FET and the turn-on of bottom FET. After a short
propagation delay (t
) from PWM falling edge, the top
gate falls (t
). As the inductor current commutates from
the top FET to the body diode of the bottom FET, the phase
node falls. The adaptive circuit in the SC1218 detects the
phase node voltage. It holds the bottom FET off until the
phase node voltage drops below 1.0V. This prevents the
top and bottom FETs from conducting simultaneously
(shoot-through). If the phase node voltage remains high
during the transition for a preset maximum BG turn on
delay (t
) , then the bottom gate will be turned on.
This supports the CROWBAR function and the sinking cur-
rent capacity required from dynamic VID operation.
Narrow PWM Pulse Filtering
During a load transient, soft start, or soft shutdown of the
voltage regulator, the PWM controller may generate a very
narrow pulse for the driver. The pulse is so narrow that it
reaches the rising edge threshold of the SC1218 at one
point then immediately falls below the falling edge thresh-
old. To prevent the SC1218 from reacting to such narrow
PWM pulses, which may cause driver output ringing or
shoot through, advanced PWM timing circuitry is added to
ease the gate transitions. A minimum off-time (typically
140ns) for the bottom gate and a minimum on-time (typi-
cally 40ns) for the top gate are enforced to make the op-
eration safe under such conditions.
Dynamic VID Operation
Some processors changes VID dynamically during opera-
tion (Dynamic VID operation). A dynamic VID can occur
under light load or heavy load conditions. At light load, it
can force the converter to sink current. After turn-off of
the top FET, the reversed inductor current flows through
the body diode of the top FET instead of the bottom FET.
As a result, the phase node voltage remains high and voids
the adaptive circuit. SC1218 features a maximum BG
turn on delay (t
) to override the adaptive delay to
turn the bottom FET on. The preset maximum BG turn on
delay time (t
) from the PWM falling egde to the
bottom gate turn-on is set to be 175ns.
Switching F
The SC1218 is capable of providing more than 3.5A peak
drive current, and operating up to 2MHz PWM frequency
without causing thermal stress on the driver. The selec-
tion of switching frequency, together with inductor and
FETs is a trade-off between the cost, size, and thermal
management of a multi-phase voltage regulator. Typically,
these parameters could be in the range of:
req
uency, Inductor and MOSFETs
a) Switching Frequency: 100kHz to 500kHz per phase
b) Inductor Value: 0.2uH to 2uH
c) MOSFETs: 4mOhm to 20mOhm R
DS(ON)
and 20nC
to 100nC total gate charge
Bootstrap and Chip Decoupling Capacitors
The top gate driver of the SC1218 is a DRN refered gate
drive whose supply voltage is derived from a bootstrap
circuit comprising a capacitor,C
, and a built-in diode.
The capacitor value can be calculated based on the total
gate charge of the top FET, Q
, and an allowed voltage
ripple on the capacitor,
V
BST
, in one PWM cycle:
BST
TOP
V
BST
Q
C
>
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| SC1218MLTRT | High Speed Synchronous MOSFET Driver |
| SC1218STRT | High Speed Synchronous MOSFET Driver |
| SC1301AISKTR | 2A High Speed Low-Side MOSFET Driver in SOT-23 |
| SC1301A | 2A High Speed Low-Side MOSFET Driver in SOT-23 |
| SC1301AISKTRT | 2A High Speed Low-Side MOSFET Driver in SOT-23 |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| SC1218MLTRT | 制造商:SEMTECH 制造商全稱:Semtech Corporation 功能描述:High Speed Synchronous MOSFET Driver |
| SC1218STRT | 制造商:SEMTECH 制造商全稱:Semtech Corporation 功能描述:High Speed Synchronous MOSFET Driver |
| SC121EVB | 制造商:SEMTECH 制造商全稱:Semtech Corporation 功能描述:Low Voltage Synchronous Boost Regulator |
| SC121NAGTR | 制造商:SILAN 制造商全稱:Silan Microelectronics Joint-stock 功能描述:LI+ BATTERY PROTECTION CIRCUIT |
| SC121NATR | 制造商:SILAN 制造商全稱:Silan Microelectronics Joint-stock 功能描述:LI+ BATTERY PROTECTION CIRCUIT |
發(fā)布緊急采購，3分鐘左右您將得到回復(fù)。