參數(shù)資料
型號(hào)： LTC3879IUD#PBF
廠商： LINEAR TECHNOLOGY CORP
元件分類： 穩(wěn)壓器
英文描述： SWITCHING CONTROLLER, PQCC16
封裝： 3 X 3 MM, LEAD FREE, PLASTIC, MO-220WEED-4, QFN-16
文件頁(yè)數(shù)： 7/28頁(yè)
文件大?。?/td> 302K
代理商： LTC3879IUD#PBF
LTC3879
15
3879f
APPLICATIONS INFORMATION
Top MOSFET Driver Supply (CB, DB)
An external bootstrap capacitor, CB,connectedtotheBOOST
pin supplies the gate drive voltage for the topside MOSFET.
This capacitor is charged through diode DB from INTVCC
when the switch node is low. When the top MOSFET turns
on, the switch node rises to VIN and the BOOST pin rises
to approximately VIN + INTVCC. The boost capacitor needs
to store approximately 100 times the gate charge required
by the top MOSFET. In most applications 0.1μF to 0.47μF,
X5R or X7R dielectric capacitor is adequate.
It is recommended that the BOOST capacitor be no larger
than 10% of the INTVCC capacitor CVCC, to ensure that
the CVCC can supply the upper MOSFET gate charge and
BOOST capacitor under all operating conditions. Variable
frequency in response to load steps offers superior tran-
sient performance but requires higher instantaneous gate
drive. Gate charge demands are greatest in high frequency
low duty factor applications under high dI/dt load steps
and at start-up.
Setting Output Voltage
The LTC3879 output voltage is set by an external feed-
back resistive divider carefully placed across the output,
as shown in Figure 5. The regulated output voltage is
determined by:
VV
R
OUT
B
A
=+
06
1
.
To improve the transient response, a feed-forward ca-
pacitor, CFF, may be used. Great care should be taken to
route the VFB line away from noise sources, such as the
inductor or the SW line.
Discontinuous Mode Operation and MODE Pin
The MODE pin determines whether the LTC3879 operates in
forced continuous mode or allows discontinuous conduc-
tion mode. Tying this pin above 0.8V enables discontinuous
operation, where the bottom MOSFET turns off when the
inductor current reverses polarity. The load current at
which current reverses and discontinuous operation begins
depends on the amplitude of the inductor ripple current and
will vary with changes in VIN. In steady-state operation,
discontinuous conduction mode occurs for DC load cur-
rents less than 1/2 the peak-to-peak ripple current. Tying
the MODE pin below the 0.8V threshold forces continuous
switching, where inductor current is allowed to reverse at
light loads and maintain synchronous switching.
In addition to providing a logic input to force continuous
operation, the MODE pin provides a means to maintain
a y back winding output when the primary is operating
in discontinuous mode. The secondary output VOUT2 is
normally set as shown in Figure 6 by the turns ratio N
of the transformer. However, if the controller goes into
discontinuous mode and halts switching due to a light
primary load current, then VOUT2 will droop. An external
resistor divider from VOUT2totheMODEpinsetsaminimum
voltage VOUT2(MIN) below which continuous operation is
forced until VOUT2 has risen above its minimum.
VV
R
OUT MIN
2
08
1
4
3
()
.
=+
Figure 6. Secondary Output Loop
Figure 5. Setting Output Voltage
LTC3879
VFB
VOUT
RB
CFF
RA
3879 F05
MODE
SW
TG
Si4884
3879 F06
LTC3879
BG
R3
R4
PGND
SGND
Si4874
VIN
CIN
COUT
COUT2
VIN
VOUT2
VOUT
1N4148
相關(guān)PDF資料
PDF描述
LTC3880IUJ-1#TRPBF 0.1 A DUAL SWITCHING CONTROLLER, 1000 kHz SWITCHING FREQ-MAX, PQCC40
LTC3880IUJ#PBF 0.1 A DUAL SWITCHING CONTROLLER, 1000 kHz SWITCHING FREQ-MAX, PQCC40
LTC3880EUJ-1#TRPBF 0.1 A DUAL SWITCHING CONTROLLER, 1000 kHz SWITCHING FREQ-MAX, PQCC40
LTC3880EUJ-1#PBF 0.1 A DUAL SWITCHING CONTROLLER, 1000 kHz SWITCHING FREQ-MAX, PQCC40
LTC3880IUJ-1#PBF 0.1 A DUAL SWITCHING CONTROLLER, 1000 kHz SWITCHING FREQ-MAX, PQCC40
相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
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LTC3880EUJ#TRPBF 功能描述:IC REG CTRLR BUCK PWM CM 40-QFN RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:PolyPhase® 標(biāo)準(zhǔn)包裝:4,500 系列:PowerWise® PWM 型:控制器 輸出數(shù):1 頻率 - 最大:1MHz 占空比:95% 電源電壓:2.8 V ~ 5.5 V 降壓:是 升壓:無(wú) 回掃:無(wú) 反相:無(wú) 倍增器:無(wú) 除法器:無(wú) Cuk:無(wú) 隔離:無(wú) 工作溫度:-40°C ~ 125°C 封裝/外殼:6-WDFN 裸露焊盤(pán) 包裝:帶卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名稱:LM1771SSDX
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