LTC3586_15 Datasheet, PDF (32/36 Pages) Linear Technology – High Efficiency USB Power Manager with Boost, Buck-Boost and Dual Bucks

LTC3586/LTC3586-1
Applications Information
0.8V
ERROR
AMP
FB3
V_OUT3
R1
V_C3 ^CP1
R2
3586 F08
Figure 8. Error Amplifier with Type I Compensation
V_OUT3
ERROR
AMP
0.8V
FB3
V_C3
C2
R2
C1
R3
R1
C3
R_FB
3586 F09
Figure 9. Error Amplifier with Type III Compensation
L
V_IN4
SW4
LTC3586/
LTC3586-1
V_OUT4
C_PL
FB4
R1
C_OUT
R2
3586 F10
Figure 10. Boost Converter Application Circuit
Boost Regulator Output Voltage Programming
The boost regulator can be programmed for output volt-
ages up to 5V. The output voltage is programmed using a
resistor divider from the V_OUT4 pin connected to the FB4
pin such that:
V_OUT
4
=
V_FB4


R1
R2
+
1^{}
where V_FB4 is 0.8V. See Figure 10.
Typical values for R1 are in the range of 40k to 1M. Too
small a resistor will result in a large quiescent current
in the feedback network and may hurt efficiency at low
current. Too large a resistor coupled with the FB4 pin ca-
pacitance will create an additional pole which may result
in loop instability. If large values are chosen for R1 and
R2, a phase-lead capacitor, C_PL, across resistor R1 can
improve the transient response. Recommended values
for C_PL are in the range of 2pF to 10pF.
Printed Circuit Board Layout Considerations
In order to be able to deliver maximum current under all
conditions, it is critical that the Exposed Pad on the backside
of the LTC3586/LTC3586-1 packages be soldered to the PC
board ground. Failure to make thermal contact between
the Exposed Pad on the backside of the package and the
copper board will result in higher thermal resistances.
3586fb
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