參數(shù)資料
型號(hào)： LT3508IUF#TR
廠商： LINEAR TECHNOLOGY CORP
元件分類： 穩(wěn)壓器
英文描述： 3.2 A DUAL SWITCHING CONTROLLER, 1060 kHz SWITCHING FREQ-MAX, PQCC24
封裝： 4 X 4 MM, PLASTIC, MO-220WGGD-X, QFN-24
文件頁(yè)數(shù)： 7/24頁(yè)
文件大?。?/td> 365K
代理商： LT3508IUF#TR
LT3508
15
3508f
is much lower than the switching frequency. A phase-lead
capacitor (CPL) across the feedback divider may improve
the transient response.
Shutdown and Undervoltage Lockout
Figure 7 shows how to add undervoltage lockout (UVLO)
to the LT3508. Typically, UVLO is used in situations where
the input supply is current limited, or has a relatively high
source resistance. A switching regulator draws constant
power from the source, so source current increases as
source voltage drops. This looks like a negative resistance
load to the source and can cause the source to current limit
or latch low under low source voltage conditions. UVLO
prevents the regulator from operating at source voltages
where the problems might occur.
An internal comparator will force the part into shutdown
below the minimum VIN1 of 3.7V. This feature can be
used to prevent excessive discharge of battery-operated
systems.
If an adjustable UVLO threshold is required, the
SHDN
pin can be used. The threshold voltage of the
SHDN pin
comparator is 2.63V. Current hysteresis is added above the
SHDNthreshold.Thiscanbeusedtosetvoltagehysteresis
of the UVLO using the following:
R
VV
A
R
V
VV
R
A
HL
H
3
75
4
263
3
8
=
–
.
–.
–
Example: switching should not start until the input is above
4.75V and is to stop if the input falls below 4V.
VV V
V
R
VV
A
k
R
HL
==
=
475
40
3
475
4
75
100
4
2
.,
.
.–
.
.6
63
475
263
100
8
200
V
VV
k
A
k
.– .
–
=
Keep the connection from the resistor to the
SHDN pin
short and make sure the interplane or surface capacitance
to switching nodes is minimized. If high resistor values are
used, the
SHDNpinshouldbebypassedwitha1nFcapacitor
to prevent coupling problems from the switch node.
Soft-Start
The output of the LT3508 regulates to the lowest voltage
present at either the TRACK/SS pin or an internal 0.8V
reference. A capacitor from the TRACK/SS pin to ground
is charged by an internal 1.2μA current source resulting
in a linear output ramp from 0V to the regulated output
whose duration is given by:
t
CV
A
RAMP
SS
=
.
08
12
At power up, internal open-collector ouputs discharge
both TRACK/SS pins. The pins clamp at 1.3V.
APPLICATIONS INFORMATION
–
+
0.8V
VSW
VC
LT3508
GND
3508 F06
R1
OUTPUT
ESR
CF
CC
RC
2M
ERROR
AMPLIFIER
FB
R2
C1
CURRENT MODE
POWER STAGE
gm = 2.5S
gm =
300
S
+
POLYMER
OR
TANTALUM
CERAMIC
CPL
Figure 6. Model for Loop Response
Figure 7. Undervoltage Lockout
2.6V
7.5
A
8
A
R3
R4
C1
SHDN
LT3508
VIN
TRACK/SS
VC
3508 F07
–
+
相關(guān)PDF資料
PDF描述
LT3508IUF 3.2 A DUAL SWITCHING CONTROLLER, 1060 kHz SWITCHING FREQ-MAX, PQCC24
LT3508IFE#TR 3.2 A DUAL SWITCHING CONTROLLER, 1060 kHz SWITCHING FREQ-MAX, PDSO16
LT3508EUF 3.2 A DUAL SWITCHING CONTROLLER, 1060 kHz SWITCHING FREQ-MAX, PQCC24
LT3509HMSE#TRPBF 1.2 A DUAL SWITCHING CONTROLLER, 2500 kHz SWITCHING FREQ-MAX, PDSO16
LT3509IMSE#PBF 1.2 A DUAL SWITCHING CONTROLLER, 2500 kHz SWITCHING FREQ-MAX, PDSO16
相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
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