參數(shù)資料
型號: LTC3700
廠商: Linear Technology Corporation
英文描述: Constant Frequency Step-Down DC/DC Controller with LDO Regulator
中文描述: 恒頻降壓DC / DC控制器LDO穩(wěn)壓器
文件頁數(shù): 14/16頁
文件大?。?/td> 209K
代理商: LTC3700
14
LTC3700
3700f
Figure 4. Setting Output Voltage (Buck Controller)
9
V
FB
V
OUT1
LTC3700
R1
3700 F04
R2
Figure 5. Foldback Current Limiting
V
FB
I
TH
/RUN
V
OUT1
LTC3700
R1
3700 F05
R2
9
10
D
FB1
D
FB2
+
Setting Output Voltage (Buck Controller)
The buck develops a 0.8V reference voltage between the
feedback (Pin 9) terminal and ground (see Figure 4). By
selecting resistor R1, a constant current is caused to flow
through R1 and R2 to set the overall output voltage. The
regulated output voltage is determined by:
V
R
R
OUT1
0 8 1
.
2
1
=
+
For most applications, an 80k resistor is suggested for R1.
To prevent stray pickup, locate resistors R1 and R2 close
to LTC3700.
Foldback Current Limiting
As described in the Output Diode Selection, the worst-
case dissipation occurs with a short-circuited output
when the diode conducts the current limit value almost
continuously. To prevent excessive heating in the diode,
3
V
OUT2
R3
3700 F06
R4
V
FB2
2
LDO
LTC3700
Figure 6. Setting Output Voltage (LDO Regulator)
APPLICATIO
S I
FOR
ATIO
U
W
U
U
foldback current limiting can be added to reduce the
current in proportion to the severity of the fault.
Foldback current limiting is implemented by adding di-
odes D
FB1
and D
FB2
between the output and the I
TH
/RUN
pin as shown in Figure 5. In a hard short (V
OUT
= 0V), the
current will be reduced to approximately 50% of the
maximum output current.
Setting Output Voltage (LDO Regulator)
The LDO develops a 0.8V reference voltage between V
FB2
(Pin 3) and ground (see Figure 6), similar to the buck
controller. The regulated output voltage V
OUT2
is given by:
V
R
R
OUT2
0 8 1
.
4
3
=
+
For most applications, an 80k resistor is suggested for R3.
To prevent stray pickup, locate resistors R3 and R4 close
to LTC3700.
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