LTC3589_1 Datasheet, PDF (24/46 Pages) Linear Technology – 8-Output Regulator with Sequencing and I2C

LTC3589
OPERATION
Table 8. Inductors for Step-Down Switching Regulators 2 and 3
MANUFACTURERS
PART NUMBER
VALUE
(µH) DCR (Ω)
Coilcraft
XPL4020-102ML
XPL4020-152ML
XPL4020-472ML
1.0
0.029
1.5
0.036
4.7
0.130
Cooper
SD14-1R2-R
SD14-3R2-R
SD25-3R3-R
1.2
0.034
3.2
0.066
3.3
0.038
Sumida
CDRH5D16NP-4R7N
4.7
CDRH38D16RHPNP-3R3M 3.3
0.064
0.059
TDK
VLF5014ST-2R2N2R3
2.2
0.073
VLCF5020T-2R7N2R2-1
2.7
0.083
VLCF5020T-3R3N2R0-1
3.3
0.096
TOKO
1124BS-2R4N
1124BS-3R3N
2.4
0.065
3.3
0.074
Tokin
H-DI-0520-3R3
H-DI-0520-4R7
H-DI-0630-3R8
H-DI-0630-4R7
3.3
0.062
4.7
0.090
3.8
0.040
4.7
0.043
Wurth
744043004
744052002
7440530047
744042003
7440430022
4.7
0.052
2.5
0.030
4.7
0.030
3.3
0.055
2.2
0.023
MAX DC
CURRENT (A)
4.00
3.60
1.90
3.35
2.00
2.21
2.05
1.46
2.3
2.2
2
2.30
2.10
2.00
1.80
2.00
1.90
1.55
2.4
2.4
1.95
2.5
SIZE (mm) W × L × H
4.2 × 4.2 × 2.0
4.2 × 4.2 × 2.0
4.2 × 4.2 × 2.0
5.2 × 5.2 × 1.45
5.2 × 5.2 × 1.45
4.8 × 4.8 × 2.5
5.6 × 5.6 × 1.8
4.2 × 4.2 × 1.8
4.8 × 4.6 × 1.4
5.0 × 5.0 × 2.0
5.0 × 5.0 × 2.0
4.5 × 4.7 × 1.8
4.5 × 4.7 × 1.8
5.3 × 5.3 × 2.0
5.3 × 5.3 × 2.0
6.3 × 6.3 × 3.0
6.3 × 6.3 × 3.0
5.0 × 5.0 × 3.0
5.8 × 5.8 × 1.8
5.8 × 5.8 × 2.8
4.8 × 4.8 × 1.8
4.8 × 4.8 × 2.8
The value of R1 plays a role in setting the dynamics of
the buck-boost voltage mode control loop. In general, a
larger value for R1 will increase stability but reduce the
speed of the transient response. A good starting point is
to choose R1 equal to 1MΩ and calculate the value of R2
needed to set the target output voltage. If a large output
capacitor is used, the bandwidth of the converter is reduced
and R1 may be reduced to improve transient response. If
a large inductor or small output capacitor is used then a
larger R1 should be used to bring the loop toward more
stable operation.
Operating Modes
Table 9 shows the I²C command registers used to control
the operating modes of the LTC3589 buck-boost converter.
When command register SCR1 bit 6 is LOW, the LTC3589
buck-boost switching regulator operates in a fixed fre-
quency pulse width modulation mode using voltage mode
feedback control. A proprietary switching algorithm allows
the converter to transition between buck, buck-boost, and
boost modes without discontinuity in inductor current or
loop characteristics. The switch topology is shown in the
application circuit in Figure 4.
Table 9. Buck-Boost Command Register Settings
COMMAND
VALUE SETTING
REGISTER[BIT]
SCR1[6]
0* Continuous Mode
1 Burst Mode Operation
OVEN[3]
0* Disable
1 Enable
SCR2[3]
0* Wait for Output Below 300mV Before Enable
1 Enable Immediately
* Denotes Default Power-On Value
When the input voltage is significantly greater than the
output voltage, the buck-boost converter operates in
buck mode. Switch D turns on continuously and switch C
remains off. Switches A and B are pulse width modulated
to produce the required duty cycle to support the output
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