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LTC3810 参数 Datasheet PDF下载

LTC3810图片预览
型号: LTC3810
PDF下载: 下载PDF文件 查看货源
内容描述: 60V低IQ ,双通道,两相同步降压型 [60V Low IQ, Dual, 2-Phase Synchronous Step-Down]
分类和应用:
文件页数/大小: 40 页 / 464 K
品牌: Linear Systems [ Linear Systems ]
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LTC3890  
applicaTions inForMaTion  
TheTypicalApplicationonthefirstpageisabasicLTC3890  
application circuit. LTC3890 can be configured to use  
either DCR (inductor resistance) sensing or low value  
resistor sensing. The choice between the two current  
sensing schemes is largely a design trade-off between  
cost, power consumption and accuracy. DCR sensing  
is becoming popular because it saves expensive current  
sensing resistors and is more power efficient, especially  
in high current applications. However, current sensing  
resistors provide the most accurate current limits for the  
controller. Other external component selection is driven  
by the load requirement, and begins with the selection of  
Filter components mutual to the sense lines should be  
placed close to the LTC3890, and the sense lines should  
run close together to a Kelvin connection underneath the  
current sense element (shown in Figure 3). Sensing cur-  
rent elsewhere can effectively add parasitic inductance  
and capacitance to the current sense element, degrading  
the information at the sense terminals and making the  
programmed current limit unpredictable. If inductor DCR  
sensing is used (Figure 4b), sense resistor R1 should be  
TO SENSE FILTER,  
NEXT TO THE CONTROLLER  
C
OUT  
R
(if R  
is used) and inductor value. Next, the  
SENSE  
SENSE  
3890 F03  
powerMOSFETsandSchottkydiodesareselected. Finally,  
input and output capacitors are selected.  
INDUCTOR OR R  
SENSE  
Figure 3. Sense Lines Placement with Inductor or Sense Resistor  
Current Limit Programming  
V
V
IN  
IN  
INTV  
CC  
The ILIM pin is a tri-level logic input which sets the maxi-  
mumcurrentlimitofthecontroller.WhenILIM isgrounded,  
the maximum current limit threshold voltage of the cur-  
rent comparator is programmed to be 30mV. When ILIM  
is floated, the maximum current limit threshold is 75mV.  
When ILIM is tied to INTVCC, the maximum current limit  
threshold is set to 50mV.  
BOOST  
TG  
R
SENSE  
SW  
V
OUT  
LTC3890  
BG  
R1*  
+
SENSE  
PLACE CAPACITOR NEAR  
SENSE PINS  
C1*  
SENSE  
SGND  
+
SENSE and SENSE Pins  
+
*R1 AND C1 ARE OPTIONAL.  
3890 F04a  
The SENSE and SENSE pins are the inputs to the cur-  
rent comparators. The common mode voltage range on  
these pins is 0V to 28V (abs max), enabling the LTC3890  
to regulate output voltages up to a nominal 24V (allowing  
margin for tolerances and transients).  
(4a) Using a Resistor to Sense Current  
V
V
IN  
IN  
INTV  
CC  
INDUCTOR  
BOOST  
TG  
+
The SENSE pin is high impedance over the full common  
L
DCR  
mode range, drawing at most 1µA. This high impedance  
allows the current comparators to be used in inductor  
DCR sensing.  
SW  
V
OUT  
LTC3890  
BG  
R1  
C1* R2  
+
The impedance of the SENSE pin changes depending on  
SENSE  
the common mode voltage. When SENSE is less than  
SENSE  
INTV – 0.5V, a small current of less than 1µA flows out  
CC  
SGND  
of the pin. When SENSE is above INTV + 0.5V, a higher  
CC  
3890 F04b  
R2  
R1 + R2  
L
||  
(R1 R2) C1 =  
*PLACE C1 NEAR  
SENSE PINS  
R
= DCR  
SENSE(EQ)  
current (~700µA) flows into the pin. Between INTV  
DCR  
CC  
0.5V and INTV + 0.5V, the current transitions from the  
CC  
(4b) Using the Inductor DCR to Sense Current  
Figure 4. Current Sensing Methods  
smaller current to the higher current.  
3890fb  
15