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参数资料
| 型号： | LTC1909-8EG#TRPBF |
| 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： | 2,000 |
| 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： | 带卷 (TR) |
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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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| LTC1911EMS8-1.5#PBF | 功能描述:IC REG BUCK 1.5V 0.25A 8MSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 标准包装:2,500 系列:- 类型:升压（升压） 输出类型:可调式 输出数:1 输出电压:1.24 V ~ 30 V 输入电压:1.5 V ~ 12 V PWM 型:电流模式，混合 频率 - 开关:600kHz 电流 - 输出:500mA 同步整流器:无 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:8-SOIC（0.154"，3.90mm 宽） 包装:带卷 (TR) 供应商设备封装:8-SOIC |
| LTC1911EMS8-1.5#TR | 功能描述:IC REG BUCK 1.5V 0.25A 8MSOP RoHS:否 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 标准包装:2,500 系列:- 类型:升压（升压） 输出类型:可调式 输出数:1 输出电压:1.24 V ~ 30 V 输入电压:1.5 V ~ 12 V PWM 型:电流模式，混合 频率 - 开关:600kHz 电流 - 输出:500mA 同步整流器:无 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:8-SOIC（0.154"，3.90mm 宽） 包装:带卷 (TR) 供应商设备封装:8-SOIC |
| LTC1911EMS8-1.5#TRPBF | 功能描述:IC REG BUCK 1.5V 0.25A 8MSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 标准包装:2,500 系列:- 类型:升压（升压） 输出类型:可调式 输出数:1 输出电压:1.24 V ~ 30 V 输入电压:1.5 V ~ 12 V PWM 型:电流模式，混合 频率 - 开关:600kHz 电流 - 输出:500mA 同步整流器:无 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:8-SOIC（0.154"，3.90mm 宽） 包装:带卷 (TR) 供应商设备封装:8-SOIC |
| LTC1911EMS8-1.8 | 功能描述:IC REG BUCK 1.8V 0.25A 8MSOP RoHS:否 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 标准包装:2,500 系列:- 类型:升压（升压） 输出类型:可调式 输出数:1 输出电压:1.24 V ~ 30 V 输入电压:1.5 V ~ 12 V PWM 型:电流模式，混合 频率 - 开关:600kHz 电流 - 输出:500mA 同步整流器:无 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:8-SOIC（0.154"，3.90mm 宽） 包装:带卷 (TR) 供应商设备封装:8-SOIC |
| LTC1911EMS8-1.8#PBF | 功能描述:IC REG BUCK 1.8V 0.25A 8MSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 标准包装:250 系列:- 类型:降压（降压） 输出类型:固定 输出数:1 输出电压:1.2V 输入电压:2.05 V ~ 6 V PWM 型:电压模式 频率 - 开关:2MHz 电流 - 输出:500mA 同步整流器:是 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:6-UFDFN 包装:带卷 (TR) 供应商设备封装:6-SON（1.45x1） 产品目录页面:1032 (CN2011-ZH PDF) 其它名称:296-25628-2 |
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