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| 型号： | LTC1909-8EG |
| 厂商： | Linear Technology |
| 文件页数： | 21/32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
0.8V threshold forces continuous synchronous operation,
allowing current to reverse at light loads and maintaining
high frequency operation.
V IN
+
V IN
C IN
1N4148
V SEC
In addition to providing a logic input to force continuous
operation, the FCB pin provides a means to maintain a
flyback winding output when the primary is operating in
OPTIONAL
EXTV CC
CONNECTION
5V < V SEC < 7V
R4
TG
LTC1909-8
EXTV CC SW
FCB SENSE +
T1
1:N
? +
+
C SEC
1 μ F
V OUT
C OUT
discontinuous mode. The secondary output V SEC is nor-
mally set as shown in Figure 4 by the turns ratio N of the
transformer. However, if the controller goes into discon-
R3
SGND
BG
PGND
19098 F04
tinuous mode and halts switching due to a light primary
load current, then V SEC will droop. An external resistor
divider from V SEC to the FCB pin sets a minimum voltage
V SEC(MIN) below which continuous operation is forced
until V SEC has risen above its minimum.
Figure 4. Secondary Output Loop and EXTV CC Connection
reasonable assumption is that the minimum R DS(ON) lies
the same amount below the typical value as the maximum
lies above it. Consult the MOSFET manufacturer for further
V SEC ( MIN ) = 0 . 8 V ? 1 +
?
?
?
R 4 ?
R 3 ?
guidelines.
To further limit current in the event of a short circuit to
ground, the LTC1909-8 includes foldback current limiting.
Fault Conditions: Current Limit and Foldback
The maximum inductor current is inherently limited in a
current mode controller by the maximum sense voltage. In
the LTC1909-8, the maximum sense voltage is controlled
by the voltage on the V RNG pin. With valley current control,
the maximum sense voltage and the sense resistance
determine the maximum allowed inductor valley current.
The corresponding output current limit is:
If the output falls by more than 25%, then the maximum
sense voltage is progressively lowered to about one sixth
of its full value.
Minimum Off-time and Dropout Operation
The minimum off-time t OFF(MIN) is the smallest amount of
time that the LTC1909-8 is capable of turning on the
bottom MOSFET, tripping the current comparator and
+ ? I L
I LIMIT =
V SNS ( MAX )
R DS ( ON ) ρ T
1
2
turning the MOSFET back off. This time is generally about
300ns. The minimum off-time limit imposes a maximum
duty cycle of t ON /(t ON + t OFF(MIN) ). If the maximum duty
t ON + t OFF ( MIN )
The current limit value should be checked to ensure that
I LIMIT(MIN) > I OUT(MAX) . The minimum value of current limit
generally occurs with the largest V IN at the highest ambi-
ent temperature, conditions that cause the largest power
loss in the converter. Note that it is important to check for
self-consistency between the assumed MOSFET junction
temperature and the resulting value of I LIMIT which heats
the MOSFET switches.
Caution should be used when setting the current limit
based upon the R DS(ON) of the MOSFETs. The maximum
current limit is determined by the minimum MOSFET on-
resistance. Data sheets typically specify nominal and
maximum values for R DS(ON) , but not a minimum. A
cycle is reached, due to a dropping input voltage for
example, then the output will drop out of regulation. The
minimum input voltage to avoid dropout is:
V IN ( MIN ) = V OUT
t ON
INTV CC Regulator
An internal P-channel low dropout regulator produces the
5V supply that powers the drivers and internal circuitry
within the LTC1909-8. The INTV CC pin can supply up to
50mA RMS and must be bypassed to ground with a
minimum of 4.7 μ F tantalum or other low ESR capacitor.
Good bypassing is necessary to supply the high transient
19098f
21
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相关代理商/技术参数 |
参数描述 |
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| LTC1909-8EG#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 28-SSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 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 |
| LTC1909-8EG#TR | 功能描述:IC REG CTRLR BUCK PWM CM 28-SSOP RoHS:否 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 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 |
| LTC1909-8EG#TRPBF | 功能描述:IC REG CTRLR BUCK PWM CM 28-SSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 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 |
| 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 |
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