參數(shù)資料
型號(hào): LTC3835IUFD#TR
廠商: LINEAR TECHNOLOGY CORP
元件分類(lèi): 穩(wěn)壓器
英文描述: 3 A SWITCHING CONTROLLER, 580 kHz SWITCHING FREQ-MAX, PQCC20
封裝: 4 X 5 MM, PLASTIC, MO-220, QFN-20
文件頁(yè)數(shù): 8/30頁(yè)
文件大?。?/td> 1775K
代理商: LTC3835IUFD#TR
LTC3835
16
3835fd
APPLICATIONS INFORMATION
Tracking and Soft-Start (TRACK/SS Pin)
The start-up of VOUT is controlled by the voltage on the
TRACK/SS pin. When the voltage on the TRACK/SS pin is
lessthantheinternal0.8Vreference,theLTC3835regulates
the VFB pin voltage to the voltage on the TRACK/SS pin
instead of 0.8V. The TRACK/SS pin can be used to program
an external soft-start function or to allow VOUT to “track”
another supply during start-up.
Figure 3. Using the TRACK/SS Pin to Program Soft-Start
LTC3835
TRACK/SS
CSS
SGND
3835 F03
Soft-start is enabled by simply connecting a capacitor
from the TRACK/SS pin to ground, as shown in Figure 3.
An internal 1A current source charges up the capacitor,
providing a linear ramping voltage at the TRACK/SS pin.
The LTC3835 will regulate the VFB pin (and hence VOUT)
according to the voltage on the TRACK/SS pin, allowing
VOUT to rise smoothly from 0V to its final regulated value.
The total soft-start time will be approximately:
tSS = CSS
0.8V
1
A
Alternatively, the TRACK/SS pin can be used to track two
(or more) supplies during start-up, as shown qualitatively
in Figures 4a and 4b. To do this, a resistor divider should
be connected from the master supply (VX) to the TRACK/
SS pin of the slave supply (VOUT), as shown in Figure 5.
During start-up VOUT will track VX according to the ratio
set by the resistor divider:
VX
VOUT
=
RA
RTRACKA
RTRACKA + RTRACKB
RA + RB
For coincident tracking (VOUT = VX during start-up),
RA = RTRACKA
RB = RTRACKB
TIME
(4a) Coincident Tracking
VX(MASTER)
VOUT(SLAVE)
OUTPUT
VOLTAGE
3835 F04A
VX(MASTER)
VOUT(SLAVE)
TIME
3835 F04B
(4b) Ratiometric Tracking
OUTPUT
VOLTAGE
Figure 5. Using the TRACK/SS Pin for Tracking
LTC3835
VOUT
Vx
VFB
TRACK/SS
3835 F05
RB
RA
RTRACKA
RTRACKB
Figure 4. Two Different Modes of Output Voltage Tracking
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