LTC3586-1 Linear Technology, LTC3586-1 Datasheet - Page 30

• Manufacturer Part Number: LTC3586-1
• Description: High Effi ciency USB Power Manager
• Manufacturer: Linear Technology

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LTC3586/LTC3586-1
APPLICATIONS INFORMATION
Table 7. Recommended Inductors for Buck-Boost Regulator
INDUCTOR
TYPE
LPS4018
D53LC
7440430022 2.2
CDRH4D22/
HP
SD14
Buck-Boost Regulator Input/Output Capacitor
Selection
Low ESR ceramic capacitors should be used at both the
buck-boost regulator output (V
boost regulator input supply (V
X7R ceramic capacitors should be used because they
retain their capacitance over wider voltage and temperature
ranges than other ceramic types. A 22μF output capacitor is
suffi cient for most applications. The buck-boost regulator
input supply should be bypassed with a 2.2μF capacitor.
Refer to Table 6 for recommended ceramic capacitor
manufacturers.
Buck-Boost Regulator Output Voltage Programming
The buck-boost regulator can be programmed for output
voltages greater than 2.75V and less than 5.5V. The full
scale output voltage is programmed using a resistor divider
from the V
where V
30
V
OUT
3
FB3
=
(μH)
3.3
2.2
2.0
2.2
2.0
OUT3
L
V
is 0.8V. See Figure 8 or 9.
FB
MAX
3.25
2.56 0.045
3
2.2
2.5
2.5
2.4
I
(A)
pin connected to the FB3 pin such that:
DC
⎛
⎝ ⎜
R
R
2
1
0.028 4.8 × 4.8 × 2.8 Würth-Elektronik
0.044 4.7 × 4.7 × 2.4 Sumida
MAX
DCR
0.08
0.07
0.02
(Ω)
+
1
⎞
⎠ ⎟
3.9 × 3.9 × 1.7
3.9 × 3.9 × 1.7
5.0 × 5.0 × 3.0 Toko
SIZE IN mm
(L × W × H)
5.2 × 5.2 ×
1.45
OUT3
IN3
). Again, only X5R or
) as well as the buck-
MANUFACTURER
Coilcraft
www.coilcraft.com
www.toko.com
www.we-online.com
www.sumida.com
Cooper
www.cooperet.com
Closing the Feedback Loop
The LTC3586/LTC3586-1 incorporate voltage mode PWM
control. The control to output gain varies with operation
region (buck, boost, buck-boost), but is usually no greater
than 20. The output fi lter exhibits a double pole response
given by:
where C
The output fi lter zero is given by:
where R
A troublesome feature in boost mode is the right-half plane
zero (RHP), and is given by:
The loop gain is typically rolled off before the RHP zero
frequency.
A simple Type I compensation network (as shown in
Figure 8) can be incorporated to stabilize the loop but
at the cost of reduced bandwidth and slower transient
response. To ensure proper phase margin, the loop must
cross unity-gain decade before the LC double pole.
The unity-gain frequency of the error amplifi er with the
Type I compensation is given by:
Most applications demand an improved transient response
to allow a smaller output fi lter capacitor. To achieve a higher
bandwidth, Type III compensation is required. Two zeros
are required to compensate for the double-pole response.
Type III compensation also reduces any V
seen during a startup condition.
f
f
f
f
FILTER POLE
FILTER ZERO
RHPZ
UG
=
OUT
ESR
2
=
_
_
• •
2 • •
is the capacitor equivalent series resistance.
is the output fi lter capacitor.
π
π
R CP
1
=
=
1
I
OUT
•
2 π
2 π
V
• •
• •
IN
• •
1
2
L V
Hz
R
1
L C
ESR
1
OUT
•
•
OUT
C
Hz
OUT
Hz
Hz
OUT3
overshoot
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