参数资料
型号: LTC3789EGN#PBF
厂商: Linear Technology
文件页数: 16/30页
文件大小: 0K
描述: IC REG CTRLR BST PWM CM 28-SSOP
标准包装: 49
PWM 型: 电流模式
输出数: 1
频率 - 最大: 710kHz
占空比: 98%
电源电压: 4 V ~ 38 V
降压:
升压:
回扫:
反相:
倍增器:
除法器:
Cuk:
隔离:
工作温度: -40°C ~ 125°C
封装/外壳: 28-SSOP(0.154",3.90mm 宽)
包装: 管件
LTC3789
APPLICATIONS INFORMATION
R SENSE(MAX) =
I OUT(MAX,BOOST) = ?
? 140mV ? I L ? V IN(MIN)
2 ? ?
I OUT(MAX,BUCK) =
90mV ? I L
+
The Typical Application on the first page is a basic
LTC3789 application circuit. External component selec-
tion is driven by the load requirement, and begins with
the selection of R SENSE and the inductor value. Next, the
power MOSFETs are selected. Finally, C IN and C OUT are
selected. This circuit can be configured for operation up
to an input voltage of 38V.
R SENSE Selection and Maximum Output Current
R SENSE is chosen based on the required output current.
The current comparator threshold sets the peak of the
inductor current in the boost region and the maximum
inductor valley current in the buck region. In the boost
region, the maximum average load current at V IN(MIN) is:
– ?
? R SENSE V OUT
where ?I L is peak-to-peak inductor ripple current. In the
buck region, the maximum average load current is:
R SENSE 2
Figure 6 shows how I LOAD(MAX) ? R SENSE varies with in-
put and output voltage.
The maximum current sensing R SENSE value for the boost
region is:
R SENSE(MAX) =
2 ? 140mV ? V IN(MIN)
2 ? I OUT(MAX,BOOST) ? V OUT + ? I L,BOOST ? V IN(MIN)
The maximum current sensing R SENSE value for the buck
region is:
2 ? 90mV
2 ? I OUT(MAX,BUCK) – ? I L,BUCK
The final R SENSE value should be lower than the calculated
R SENSE(MAX) in both the boost and buck regions. A 20%
to 30% margin is usually recommended.
Programming Input/Output Current Limit
As shown in Figures 7 and 8, input/output current sense
resistor R SENSE2 should be placed between the bulk capaci-
tor for V IN /V OUT and the decoupling capacitor. A lowpass
filter formed by R F and C F is recommended to reduce the
switching noise and stabilize the current loop. The input/
output current limit is set by the I LIM pin for 50mV, 100mV
or 140mV with I LIM pulled to the GND, floating, or tied to
INTV CC , respectively. If input/output current limit is not
desired, the I OSENSE+ and I OSENSE– pins should be shorted
to either V OUT or V IN .
160
150
FROM
CONTROLLER
V OUT
R F
100
R SENSE2
C F
R F
100
+
TO
SYSTEM
V OUT
140
130
2
I OSENSE+
LTC3789
1
I OSENSE–
120
110
100
3789 F07
Figure 7. Programming Output Current Limit
90
0.1
1
V IN /V OUT (V)
10
3789 F06
FROM DC
POWER INPUT
+
R F
100
R SENSE2
C F
R F
100
TO DRAIN OF
SWITCH A
Figure 6. Load Current vs V IN /V OUT
2
I OSENSE+
1
I OSENSE–
LTC3789
3789 F08
Figure 8. Programming Input Current Limit
3789fa
16
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