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參數(shù)資料
| 型號： | LTC1775C |
| 廠商： | Linear Technology Corporation |
| 英文描述： | Quadruple 2-Input Positive-NAND Gate 14-TVSOP -40 to 85 |
| 中文描述： | 高功率無檢測電阻商標(biāo)電流模式同步降壓型開關(guān)穩(wěn)壓器 |
| 文件頁數(shù)： | 9/24頁 |
| 文件大小： | 289K |
| 代理商： | LTC1775C |
9
LTC1775
The basic LTC1775 application circuit is shown in Figure 1.
External component selection is primarily determined by
the maximum load current and begins with the selection of
the sense resistance for the desired current level. Since the
LTC1775 senses current using the on-resistance of the
power MOSFET, the maximum application current prima-
rily determines the choice of MOSFET. The operating
frequency and the inductor are chosen based largely on
the desired amount of ripple current. Finally, C
IN
is se-
lected for its ability to handle the RMS current into the
converter and C
OUT
is chosen with low enough ESR to
meet the output voltage ripple specification.
Power MOSFET Selection
The LTC1775 requires two external N-channel power
MOSFETs, one for the top (main) switch and one for the
bottom (synchronous) switch. Important parameters for
the power MOSFETs are the breakdown voltage V
(BR)DSS
,
threshold voltage V
GS(TH)
, on-resistance R
DS(ON)
, reverse
transfer capacitance C
RSS
and maximum current I
D(MAX)
.
The gate drive voltage is set by the 5.2V INTV
CC
supply.
Consequently, logic level threshold MOSFETs must be
used in LTC1775 applications. If low input voltage opera-
tion is expected (V
IN
< 5V), then sub-logic level threshold
MOSFETs should be used. Pay close attention to the
V
(BR)DSS
specification for the MOSFETs as well; many of
the logic level MOSFETs are limited to 30V or less.
The MOSFET on-resistance is chosen based on the
required load current. The maximum average output cur-
rent I
O(MAX)
is equal to the peak inductor current less half
the peak-to-peak ripple current
I
L
. The peak inductor
current is inherently limited in a current mode controller
by the current threshold I
TH
range. The corresponding
maximum V
DS
sense voltage is about 300mV under nor-
mal conditions. The LTC1775 will not allow peak inductor
current to exceed 300mV/R
DS(ON)(TOP)
. The following
equation is a good guide for determining the required
R
DS(ON)(MAX)
at 25
°
C (manufacturer’s specification), al-
lowing some margin for ripple current, current limit and
variations in the LTC1775 and external component values:
R
mV
)
( )
I
DS ON MAX
(
O MAX
(
T
)(
)
)
(
240
ρ
The
ρ
T
is a normalized term accounting for the significant
variation in R
DS(ON)
with temperature, typically about
0.4%/
°
C as shown in Figure 2. Junction to ambient tem-
perature T
JA
is around 20
°
C in most applications. For a
maximum ambient temperature of 70
°
C, using
ρ
90
°
C
1.3
in the above equation is a reasonable choice. This equation
is plotted in Figure 3 to illustrate the dependence of
maximum output current on R
DS(ON)
. Some popular
MOSFETs are shown as data points.
Figure 2. R
DS(ON)
vs Temperature
Figure 3. Maximum Output Current vs R
DS(ON)
at V
GS
= 4.5V
The 300mV maximum sense voltage of the LTC1775
allows a large current to be obtained from power MOSFET
switches. It also causes a significant amount of power
dissipation in those switches and careful attention must be
JUNCTION TEMPERATURE (
°
C)
–50
ρ
T
1.0
1.5
150
1775 F02
0.5
0
0
50
100
2.0
R
DS(ON)
(
)
0
M
15
20
25
0.08
1775 F03
10
5
0
0.02
0.04
0.06
0.10
IRL3803
SUD50N03-10
FDS8936A
Si9936
APPLICATIOU
W
U
U
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| LTC1775CGN | 功能描述:IC REG CTRLR BUCK PWM CM 16-SSOP RoHS:否 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:4,500 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 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 ~ 125°C 封裝/外殼:6-WDFN 裸露焊盤 包裝:帶卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名稱:LM1771SSDX |
| LTC1775CGN#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 16-SSOP RoHS:否 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:4,500 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 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 ~ 125°C 封裝/外殼:6-WDFN 裸露焊盤 包裝:帶卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名稱:LM1771SSDX |
| LTC1775CGN#TR | 功能描述:IC REG CTRLR BUCK PWM CM 16-SSOP RoHS:否 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:4,500 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 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 ~ 125°C 封裝/外殼:6-WDFN 裸露焊盤 包裝:帶卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名稱:LM1771SSDX |
| LTC1775CGN#TRPBF | 功能描述:IC REG CTRLR BUCK PWM CM 16-SSOP 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:4,500 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 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 ~ 125°C 封裝/外殼:6-WDFN 裸露焊盤 包裝:帶卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名稱:LM1771SSDX |
| LTC1775CS | 功能描述:IC REG CTRLR BUCK PWM CM 16-SOIC RoHS:否 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:4,500 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 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 ~ 125°C 封裝/外殼:6-WDFN 裸露焊盤 包裝:帶卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名稱:LM1771SSDX |
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