參數(shù)資料
型號: LT3694-1EUFD#PBF
廠商: LINEAR TECHNOLOGY CORP
元件分類: 穩(wěn)壓器
英文描述: 2.6 A SWITCHING REGULATOR, 2500 kHz SWITCHING FREQ-MAX, PQCC28
封裝: 4 X 5 MM, LEAD FREE, PLASTIC, MO-220, QFN-28
文件頁數(shù): 6/28頁
文件大小: 276K
代理商: LT3694-1EUFD#PBF
LT3694/LT3694-1
14
36941fa
Diode Selection
The catch diode (D1 from Figure 1) conducts current only
during switch off time. Average forward current in normal
operation can be calculated from:
I
D(AVG) = IOUT
V
IN VOUT
V
IN
Consider a diode with a larger current rating than ID(AVG)
when the part must survive a shorted output. The DA pin
monitors the current in the diode and prevents the switch
from turning on at the beginning of a charge cycle if the
diode current is above the DA limit. Therefore, under
overload conditions, the average diode current will in-
crease to the average of the switch current limit and the
DA current limit.
Peak reverse voltage is equal to the regulator input voltage,
so use a diode with a reverse voltage rating greater than
the maximum input voltage. The internal OVLO can protect
the diode from excessive reverse voltage by shutting down
the regulator if the input voltage exceeds 38V. Table 4 lists
several Schottky diodes and their manufacturers.
Table 4. Schottky Diodes (40V, 3A)
PART NUMBER
Vf at 3A (V)
OUTLINE
MANUFACTURER
MBRS340
MBRD340
0.5
0.6
SMC
D-PAK
ON Semiconductor
www.onsemi.com
B340
SMB340
0.5
SMC
Powermite 3
Diodes, Inc.
www.diodes.com
CMSH3-40
CSHD3-40
0.5
0.65
SMC
D-PAK
Central Semiconductor
www.centralsemi.com
Frequency Compensation
The LT3694 uses current mode control to regulate the
output. This simplifies loop compensation. In particular, the
LT3694 does not require the ESR of the output capacitor for
stability, so the user is free to employ ceramic capacitors to
achieve low output ripple and small circuit size. Frequency
compensation is provided by the components tied to the
VC pin, as shown in Figure 2. Generally a capacitor (CC)
and a resistor (RC) in series to ground are used. In addi-
tion, there may be lower value capacitor in parallel. This
capacitor (CF) is not part of the loop compensation but
is used to filter noise at the switching frequency, and is
required only if a phase-lead capacitor (CPL) is used or if
the output capacitor (C1) has high ESR.
APPLICATIONS INFORMATION
+
0.75V
SW
VC
gm =
350μS
GND
3M
LT3694
36941 F02
R1
OUTPUT
ESR
CF
CC
RC
ERROR
AMPLIFIER
FB
R2
C1
CURRENT MODE
POWER STAGE
gm = 7.5S
+
POLYMER
OR
TANTALUM
CERAMIC
CPL
Figure 2. Model for Loop Response
Loop compensation determines the stability and transient
performance. The best values for the compensation net-
work depend on the application and in particular the type
of output capacitor. A practical approach is to start with
one of the circuits in this data sheet that is similar to your
application and tune the compensation network to optimize
the performance. Stability should then be checked across all
operating conditions, including load current, input voltage
and temperature. The LT1375 data sheet contains a more
thorough discussion of loop compensation and describes
how to test the stability using a transient load. Figure 2
shows an equivalent circuit for the LT3694 control loop.
The error amplifier is a transconductance amplifier with
finite output impedance.
相關PDF資料
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LT3694-1EUFD#TRPBF 2.6 A SWITCHING REGULATOR, 2500 kHz SWITCHING FREQ-MAX, PQCC28
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