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参数资料
| 型号： | LTC1909-8EG |
| 厂商： | Linear Technology |
| 文件页数： | 18/32页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM CM 28-SSOP |
| 标准包装： | 47 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 200kHz |
| 占空比： | 90% |
| 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： | 管件 |
| 其它名称： | LTC19098EG |
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LTC1909-8
APPLICATIO S I FOR ATIO
one must carefully choose the MOSFET on-resistance as
discussed below.
Power MOSFET Selection
The power dissipated by the top and bottom MOSFETs
strongly depends upon their respective duty cycles and
the load current. When the LTC1909-8 is operating in
continuous mode, the duty cycles for the MOSFETs are:
The LTC1909-8 requires two external N-channel power
MOSFETs, one for the top (main) switch and one for the
bottom (synchronous) switch. Important parameters for
D TOP =
V OUT
V IN
= IN OUT
thepowerMOSFETsarethebreakdownvoltageV (BR)DSS ,
threshold voltage V (GS)TH , on-resistance R DS(ON) , reverse
transfer capacitance C RSS and maximum current I DS(MAX) .
The gate drive voltage is set by the 5V INTV CC supply.
Consequently, logic-level threshold MOSFETs must be
used in LTC1909-8 applications. If the input voltage is
expected to drop below 5V, then sub-logic level threshold
MOSFETs should be considered.
When the bottom MOSFET is used as the current sense
element, particular attention must be paid to its on-
resistance. MOSFET on-resistance is typically specified
with a maximum value R DS(ON)(MAX) at 25 ° C. In this case,
additional margin is required to accommodate the rise in
MOSFET on-resistance with temperature:
V – V
D BOT
V IN
The resulting power dissipation in the MOSFETs at maxi-
mum output current are:
P TOP = D TOP I OUT(MAX)2 ρ T(TOP) R DS(ON)(MAX)
+ k V IN2 I OUT(MAX) C RSS f
P BOT = D BOT I OUT(MAX)2 ρ T(BOT) R DS(ON)(MAX)
Both MOSFETs have I 2 R losses and the top MOSFET
includes an additional term for transition losses, which are
largest at high input voltages. The constant K = 1.7A –1 can
be used to estimate the amount of transition loss. The
bottom MOSFET losses are greatest when the bottom duty
cycle is near 100%, during a short-circuit or at high input
R DS ( ON )( MAX ) =
R SENSE
ρ T
voltage.
Operating Frequency
The ρ T term is a normalization factor (unity at 25 ° C)
accounting for the significant variation in on-resistance
with temperature, typically about 0.4%/ ° C as shown in
Figure 2. For a maximum temperature of 100 ° C, using a
value ρ T = 1.3 is reasonable.
2.0
1.5
The choice of operating frequency is a tradeoff between
efficiency and component size. Low frequency operation
improves efficiency by reducing MOSFET switching losses
but requires larger inductance and/or capacitance in order
to maintain low output ripple voltage.
The operating frequency of LTC1909-8 applications is
determined implicitly by the one-shot timer that controls
the on-time t ON of the top MOSFET switch. The on-time is
set by the current into the I ON pin according to:
1.0
t ON =
V VON
I ION
( 10 pF )
0.5
Tying a resistor R ON from V IN to the I ON pin yields an on-
0
– 50
0
50
100
150
time inversely proportional to V IN . For a step-down
converter, this results in approximately constant fre-
JUNCTION TEMPERATURE ( ° C)
quency operation as the input supply varies:
19098 F02
Figure 2. R DS(ON) vs. Temperature
19098f
18
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相关代理商/技术参数 |
参数描述 |
|---|---|
| 74HC273DB | 功能描述:触发器 OCTAL D-TYPE RoHS:否 制造商:Texas Instruments 电路数量:2 逻辑系列:SN74 逻辑类型:D-Type Flip-Flop 极性:Inverting, Non-Inverting 输入类型:CMOS 输出类型: 传播延迟时间:4.4 ns 高电平输出电流:- 16 mA 低电平输出电流:16 mA 电源电压-最大:5.5 V 最大工作温度:+ 85 C 安装风格:SMD/SMT 封装 / 箱体:X2SON-8 封装:Reel |
| 74HC273DB,112 | 功能描述:触发器 OCTAL D-TYPE RoHS:否 制造商:Texas Instruments 电路数量:2 逻辑系列:SN74 逻辑类型:D-Type Flip-Flop 极性:Inverting, Non-Inverting 输入类型:CMOS 输出类型: 传播延迟时间:4.4 ns 高电平输出电流:- 16 mA 低电平输出电流:16 mA 电源电压-最大:5.5 V 最大工作温度:+ 85 C 安装风格:SMD/SMT 封装 / 箱体:X2SON-8 封装:Reel |
| 74HC273DB,118 | 功能描述:触发器 OCTAL D-TYPE RoHS:否 制造商:Texas Instruments 电路数量:2 逻辑系列:SN74 逻辑类型:D-Type Flip-Flop 极性:Inverting, Non-Inverting 输入类型:CMOS 输出类型: 传播延迟时间:4.4 ns 高电平输出电流:- 16 mA 低电平输出电流:16 mA 电源电压-最大:5.5 V 最大工作温度:+ 85 C 安装风格:SMD/SMT 封装 / 箱体:X2SON-8 封装:Reel |
| 74HC273DBT | 制造商:NXP Semiconductors 功能描述:HC/UH SERIES, POSITIVE EDGE TRIGGERED D FLIP-FLOP, TRUE OUTPUT, 20 Pin Plastic SMT |
| 74HC273DB-T | 功能描述:触发器 OCTAL D-TYPE RoHS:否 制造商:Texas Instruments 电路数量:2 逻辑系列:SN74 逻辑类型:D-Type Flip-Flop 极性:Inverting, Non-Inverting 输入类型:CMOS 输出类型: 传播延迟时间:4.4 ns 高电平输出电流:- 16 mA 低电平输出电流:16 mA 电源电压-最大:5.5 V 最大工作温度:+ 85 C 安装风格:SMD/SMT 封装 / 箱体:X2SON-8 封装:Reel |
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