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| 型号： | LTC1909-8EG |
| 厂商： | Linear Technology |
| 文件页数： | 23/32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
INTV CC
shown in Figure 6a or 6c is simple, but slightly increases
3.3V OR 5V
V IN
RUN/SS
R SS *
D2*
RUN/SS
shutdown current. Connecting a resistor to INTV CC as
shown in Figure 6b and 6d eliminates the additional
D1
R SS *
shutdown current, but requires a diode to isolate C SS . Any
C SS
*OPTIONAL TO OVERRIDE OVERCURRENT LATCHOFF
C SS
pull-up network must be able to maintain RUN/SS above
the 4.2V maximum latchoff threshold and overcome the
4 μ A maximum discharge current.
(6a)
(6b)
Efficiency Considerations
V IN
RUN/SS
R SS *
INTV CC
R SS *
D2*
RUN/SS
The percent efficiency of a switching regulator is equal to
the output power divided by the input power times 100%.
It is often useful to analyze individual losses to determine
CPUON
C SS
CPUON
C SS
what is limiting the efficiency and which change would
produce the most improvement. Although all dissipative
19098 F06
*OPTIONAL TO OVERRIDE OVERCURRENT LATCHOFF
(6c) (6d)
Figure 6. RUN/SS Pin Interfacing with Latchoff Defeated
controller turns off both power MOSFETs, shutting down
the converter permanently. The RUN/SS pin must be
actively pulled down to ground in order to restart opera-
tion. If the RUN/SS pin is tied to the CPUON pin, this is
achieved by pulling the VRON pin low or by sending two
Off protocols to the SMBus VID programmer to force the
CPUON pin low.
The overcurrent protection timer requires that the soft-
start timing capacitor C SS be made large enough to guar-
antee that the output is in regulation by the time C SS has
reached the 4V threshold. In general, this will depend upon
the size of the output capacitance, output voltage and load
current characteristic. A minimum soft-start capacitor can
be estimated from:
C SS > C OUT V OUT R SENSE (10 – 4 [F/V s])
Generally 0.1 μ F is more than sufficient.
Overcurrent latchoff operation is not always needed or
desired. Load current is already limited during a short-
circuit by the current foldback circuitry and latchoff opera-
tion can prove annoying during troubleshooting. The
feature can be overridden by adding a pull-up current
greater than 5 μ A to the RUN/SS pin. The additional current
prevents the discharge of C SS during a fault and also
shortens the soft-start period. Using a resistor to V IN as
elements in the circuit produce losses, four main sources
account for most of the losses in LTC1909-8 circuits:
1. DC I 2 R losses. These arise from the resistances of the
MOSFETs, inductor and PC board traces and cause the
efficiency to drop at high output currents. In continuous
mode the average output current flows through L, but is
chopped between the top and bottom MOSFETs. If the two
MOSFETs have approximately the same R DS(ON) , then the
resistance of one MOSFET can simply be summed with the
resistances of L and the board traces to obtain the DC I 2 R
loss. For example, if R DS(ON) = 0.01 ? and R L = 0.005 ? , the
loss will range from 15mW to 1.5W as the output current
varies from 1A to 10A.
2. Transition loss. This loss arises from the brief amount
of time the top MOSFET spends in the saturated region
during switch node transitions. It depends upon the input
voltage, load current, driver strength and MOSFET
capacitance, among other factors. The loss is significant
at input voltages above 20V and can be estimated from:
Transition Loss ? (1.7A –1 ) V IN2 I OUT C RSS f
3. INTV CC current. This is the sum of the MOSFET driver
and control currents. This loss can be reduced by supply-
ing INTV CC current through the EXTV CC pin from a high
efficiency source, such as an output derived boost net-
work or alternate supply if available.
4. C IN loss. The input capacitor has the difficult job of
filtering the large RMS input current to the regulator. It
must have a very low ESR to minimize the AC I 2 R loss and
19098f
23
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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 |
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