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参数资料
| 型号： | LTC3789EUFD#TRPBF |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 稳压器 |
| 英文描述： | 0.1 A SWITCHING CONTROLLER, 710 kHz SWITCHING FREQ-MAX, PQCC28 |
| 封装： | 4 X 5 MM, LEAD FREE, PLASTIC, MO-220, QFN-28 |
| 文件页数： | 13/28页 |
| 文件大小： | 486K |
| 代理商： | LTC3789EUFD#TRPBF |
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LTC3789
20
3789f
applicaTions inForMaTion
Significant efficiency and thermal gains can be realized by
powering INTVCC from the output, since the VIN current
resultingfromthedriverandcontrolcurrentswillbescaled
by a factor of (Duty Cycle)/(Switcher Efficiency).
Tying the EXTVCC pin to a 12V output reduces the junc-
tion temperature in the previous example from 125°C
to 97°C:
TJ = 70°C + (28mA)(12V)(80°C/W) = 97°C
Powering INTVCC from the output can also provide
enough gate drive when VIN drops below 5V. This allows
a wider operating range for VIN after the controller start
into regulation.
The following list summarizes the three possible connec-
tions for EXTVCC:
1. EXTVCC left open (or grounded). This will cause INTVCC
to be powered from the internal 5.5V regulator at the
cost of a small efficiency penalty.
2. EXTVCCconnecteddirectlytoVOUT(4.7V<VOUT<14V).
This is the normal connection for the 5.5V regulator and
provides the highest efficiency.
3. EXTVCC connected to an external supply. If an external
supply is available in the 4.7V to 14V range, it may be
used to power EXTVCC provided it is compatible with
the MOSFET gate drive requirements.
Note that there is an internal body diode from INTVCC to
VIN. When INTVCC is powered from EXTVCC and VIN drops
lower than 4.5V, the diode will create a back-feeding path
from EXTVCC to VIN. To limit this back-feeding current, a
10Ω ~ 15Ω resistor is recommended between the system
VIN voltage and the chip VIN pin.
Output Voltage
The LTC3789 output voltage is set by an external feedback
resistivedividercarefullyplacedacrosstheoutputcapacitor.
Theresultantfeedbacksignaliscomparedwiththeinternal
precision 0.8V voltage reference by the error amplifier. The
output voltage is given by the equation:
VOUT = 0.8V 1+
R2
R1
where R1 and R2 are defined in Figure 13.
Topside MOSFET Driver Supply (CA, DA, CB, DB)
Referring to Figure 13, the external bootstrap capacitors
CA and CB connected to the BOOST1 and BOOST2 pins
supply the gate drive voltage for the topside MOSFET
switches A and D. When the top switch A turns on, the
switch node SW2 rises to VIN and the BOOST2 pin rises
to approximately VIN + INTVCC. When the bottom switch
B turns on, the switch node SW2 drops to low and the
boost capacitor CB is charged through DB from INTVCC.
When the top switch D turns on, the switch node SW1
rises to VOUT and the BOOST1 pin rises to approximately
VOUT + INTVCC. When the bottom switch C turns on, the
switch node SW1 drops to low and the boost capacitor CA
is charged through DA from INTVCC. The boost capacitors
CA and CB need to store about 100 times the gate charge
required by the top switches A and D. In most applica-
tions, a 0.1F to 0.47F, X5R or X7R dielectric capacitor
is adequate.
Undervoltage Lockout
The LTC3789 has two functions that help protect the
controller in case of undervoltage conditions. A precision
UVLO comparator constantly monitors the INTVCCvoltage
to ensure that an adequate gate-drive voltage is present. It
locks out the switching action when INTVCC is below 3.4V.
To prevent oscillation when there is a disturbance on the
INTVCC, the UVLO comparator has 400mV of precision
hysteresis.
Anotherwaytodetectanundervoltageconditionistomoni-
tor the VIN supply. Because the RUN pin has a precision
turn-on reference of 1.22V, one can use a resistor divider
to VIN to turn on the IC when VIN is high enough. An extra
5A of current flows out of the RUN pin once its voltage
passes 1.22V. One can program the hysteresis of the run
comparator by adjusting the values of the resistive divider.
Soft-Start Function
When a capacitor is connected to the SS pin, a soft-start
current of 3A starts to charge the capacitor. A soft-start
function is achieved by controlling the output ramp volt-
age according to the ramp rate on the SS pin. Current
foldback is disabled during this phase to ensure smooth
soft-start. When the chip is in the shutdown state with its
RUN pin voltage below 1.22V, the SS pin is actively pulled
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LTC3789IGN#PBF | 功能描述:IC REG CTRLR BST 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 |
| LTC3789IGN#TRPBF | 功能描述:IC REG CTRLR BST 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 |
| LTC3789IUFD#PBF | 功能描述:IC REG CTRLR BST PWM CM 28-QFN 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 |
| LTC3789IUFD#TRPBF | 功能描述:IC REG CTRLR BST PWM CM 28-QFN 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 |
| LTC3789IUFDPBF | 制造商:Linear Technology 功能描述:4-Switch Buck-Boost Controller QFN28EP |
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