LT3682 LINER [Linear Technology], LT3682 Datasheet - Page 16

• Manufacturer Part Number: LT3682
• Description: 1A Micropower Step-Down
• Manufacturer: LINER [Linear Technology]

APPLICATIONS INFORMATION
LT3682
Table 3. Schottky Diodes
PART NUMBER
On Semiconducor
MBR0520L
MBR0540
MBRM120E
MBRM140
Diodes Inc.
B0530W
B0540W
B120
B130
B140
B150
B220
B230
B140HB
DFLS240L
DFLS140
B240
Central Semiconductor
CMSH1 – 40M
CMSH1 – 60M
CMSH1 – 40ML
CMSH2 – 40M
CMSH2 – 60M
CMSH2 – 40L
CMSH2 – 40
CMSH2 – 60
Frequency Compensation
The LT3682 uses current mode control to regulate the
output. This simplifi es loop compensation. In particular,
the LT3682 does not require the ESR of the output capacitor
for stability, so you are free to use ceramic capacitors to
achieve low output ripple and small circuit size. Frequency
16
V
R
20
40
20
40
30
40
20
30
40
50
20
30
40
40
40
40
40
60
40
40
60
40
40
60
(V)
I
AVE
0.5
0.5
0.5
0.5
1.1
1
1
1
1
1
1
2
2
1
2
2
1
1
1
2
2
2
2
2
(A)
V
F
at 1A (mV) V
620
530
550
620
500
500
500
700
510
500
700
400
F
at 2A (mV)
595
500
500
500
500
550
700
400
500
700
compensation is provided by the components tied to the V
pin, as shown in Figure 2. Generally a capacitor (C
resistor (R
may be a lower value capacitor in parallel. This capacitor
(C
is required only if a phase-lead capacitor (C
if the output capacitor has high ESR.
Loop compensation determines the stability and transient
performance. Optimizing the design of the compensation
network depends on the application and 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 LT3682 control loop.
The error amplifi er is a transconductance amplifi er with
fi nite output impedance. The power section, consisting
of the modulator, power switch and inductor, is modeled
as a transconductance amplifi er generating an output
current proportional to the voltage at the V
the output capacitor integrates this current, and that the
F
) is used to fi lter noise at the switching frequency, and
LT3682
CURRENT MODE
POWER STAGE
C
g
F
V
m
C
= 1.25S
C
) in series to ground are used. In addition, there
R
C
C
Figure 2. Model for Loop Response
C
3Meg
g
m
= 420μS
–
+
GND
0.8V
SW
FB
R1
R2
ELECTROLITIC
TANTALUM
POLYMER
C
PL
3682 F02
OR
OR
+
C
ESR
PL
OUTPUT
C1
pin. Note that
) is used or
CERAMIC
C
) and a
C1
3682f
C