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| 型号： | LTC3827IG-1#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 15/32页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM CM 28-SSOP |
| 标准包装： | 2,000 |
| 系列： | PolyPhase® |
| PWM 型： | 电流模式 |
| 输出数： | 2 |
| 频率 - 最大： | 580kHz |
| 占空比： | 99.4% |
| 电源电压： | 4 V ~ 36 V |
| 降压： | 是 |
| 升压： | 无 |
| 回扫： | 无 |
| 反相： | 无 |
| 倍增器： | 无 |
| 除法器： | 无 |
| Cuk： | 无 |
| 隔离： | 无 |
| 工作温度： | -40°C ~ 85°C |
| 封装/外壳： | 28-SSOP（0.209"，5.30mm 宽） |
| 包装： | 带卷 (TR) |
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LTC3827-1
APPLICATIONS INFORMATION
P MAIN = OUT ( I MAX ) ( 1 + ) R DS(ON) +
( V IN ) 2
( R DR ) ( C MILLER ) ?
The MOSFET power dissipations at maximum output
current are given by:
V 2
V IN
I MAX
2
C IN and C OUT Selection
The selection of C IN is simpli?ed by the 2-phase architec-
ture and its impact on the worst-case RMS current drawn
through the input network (battery/fuse/capacitor). It can be
shown that the worst-case capacitor RMS current occurs
when only one controller is operating. The controller with
the highest (V OUT )(I OUT ) product needs to be used in the
1
V INTVCC – V THMIN
+
1
V THMIN
( f )
formula below to determine the maximum RMS capacitor
current requirement. Increasing the output current drawn
from the other controller will actually decrease the input
P SYNC =
V IN – V OUT
V IN
( I MAX ) 2 ( 1 +
) R DS(ON)
RMS ripple current from its maximum value. The out-of-
phase technique typically reduces the input capacitor’s RMS
ripple current by a factor of 30% to 70% when compared
where δ is the temperature dependency of R DS(ON) and
R DR (approximately 2Ω) is the effective driver resistance
at the MOSFET’s Miller threshold voltage. V THMIN is the
typical MOSFET minimum threshold voltage.
Both MOSFETs have I 2 R losses while the topside N-channel
equation includes an additional term for transition losses,
to a single phase power supply solution.
In continuous mode, the source current of the top MOSFET
is a square wave of duty cycle (V OUT )/(V IN ). To prevent
large voltage transients, a low ESR capacitor sized for the
maximum RMS current of one channel must be used. The
maximum RMS capacitor current is given by:
which are highest at high input voltages. For V IN < 20V
the high current ef?ciency generally improves with larger
MOSFETs, while for V IN > 20V the transition losses rapidly
C IN Required I RMS
I MAX
V IN
( V OUT ) ( V IN – V OUT )
1/2
increase to the point that the use of a higher R DS(ON) device
with lower C MILLER actually provides higher ef?ciency. The
synchronous MOSFET losses are greatest at high input
voltage when the top switch duty factor is low or during
a short-circuit when the synchronous switch is on close
to 100% of the period.
The term (1 + δ ) is generally given for a MOSFET in the
form of a normalized R DS(ON) vs Temperature curve, but
δ = 0.005/°C can be used as an approximation for low
voltage MOSFETs.
The optional Schottky diodes D3 and D4 shown in
Figure 14 conduct during the dead-time between the
conduction of the two power MOSFETs. This prevents
the body diode of the bottom MOSFET from turning on,
storing charge during the dead-time and requiring a re-
verse recovery period that could cost as much as 3% in
ef?ciency at high V IN . A 1A to 3A Schottky is generally a
good compromise for both regions of operation due to
the relatively small average current. Larger diodes result
in additional transition losses due to their larger junction
capacitance.
This formula has a maximum at V IN = 2V OUT , where I RMS
= I OUT /2. This simple worst-case condition is commonly
used for design because even signi?cant deviations do not
offer much relief. Note that capacitor manufacturers’ ripple
current ratings are often based on only 2000 hours of life.
This makes it advisable to further derate the capacitor, or
to choose a capacitor rated at a higher temperature than
required. Several capacitors may be paralleled to meet
size or height requirements in the design. Due to the high
operating frequency of the LTC3827-1, ceramic capacitors
can also be used for C IN . Always consult the manufacturer
if there is any question.
The bene?t of the LTC3827-1 2-phase operation can be
calculated by using the equation above for the higher
power controller and then calculating the loss that would
have resulted if both controller channels switched on at
the same time. The total RMS power lost is lower when
both controllers are operating due to the reduced overlap of
current pulses required through the input capacitor’s ESR.
This is why the input capacitor’s requirement calculated
above for the worst-case controller is adequate for the dual
38271fe
15
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| LTC3827IUH#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 32-QFN RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:PolyPhase® 标准包装:4,500 系列:PowerWise® PWM 型:控制器 输出数:1 频率 - 最大:1MHz 占空比:95% 电源电压:2.8 V ~ 5.5 V 降压:是 升压:无 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-40°C ~ 125°C 封装/外壳:6-WDFN 裸露焊盘 包装:带卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名称:LM1771SSDX |
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