參數(shù)資料
型號: LTC1871-7
廠商: Linear Technology Corporation
英文描述: Quadruple 2-Input Positive-AND Gate 14-SOIC -40 to 85
中文描述: 2相升壓型DC / DC控制器
文件頁數(shù): 12/36頁
文件大?。?/td> 411K
代理商: LTC1871-7
12
LTC1871
APPLICATIOU
caused by the current flowing into the FB pin during
normal operation is less than 1% (this translates to a
maximum value of R1 of about 250k).
W
U
U
Programming Turn-On and Turn-Off Thresholds
with the RUN Pin
The LTC1871 contains an independent, micropower volt-
age reference and comparator detection circuit that re-
mains active even when the device is shut down, as shown
in Figure 8. This allows users to accurately program an
input voltage at which the converter will turn on and off.
The falling threshold voltage on the RUN pin is equal to the
internal reference voltage of 1.248V. The comparator has
100mV of hysteresis to increase noise immunity.
The turn-on and turn-off input voltage thresholds are
programmed using a resistor divider according to the
following formulas:
V
V
R
R
R
R
V
V
IN OFF
(
IN ON
(
)
)
.
.
=
+
=
+
1 248
1
2
1
2
1
1 348
1
The resistor R1 is typically chosen to be less than 1M.
For applications where the RUN pin is only to be used as
a logic input, the user should be aware of the 7V
Absolute Maximum Rating for this pin!
The RUN pin can
be connected to the input voltage through an external 1M
resistor, as shown in Figure 8c, for “always on” operaton.
+
RUN
COMPARATOR
V
IN
RUN
R2
R1
INPUT
SUPPLY
OPTIONAL
FILTER
CAPACITOR
+
GND
1871 F8a
BIAS AND
START-UP
CONTROL
1.248V
μ
POWER
REFERENCE
6V
Figure 8b. On/Off Control Using External Logic
Figure 8c. External Pull-Up Resistor On
RUN Pin for “Always On” Operation
Figure 8a. Programming the Turn-On and Turn-Off Thresholds Using the RUN Pin
+
RUN
COMPARATOR
1.248V
1871 F08b
RUN
6V
EXTERNAL
LOGIC CONTROL
+
RUN
COMPARATOR
V
IN
RUN
R2
1M
INPUT
SUPPLY
+
GND
1.248V
1871 F08c
6V
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