Datasheet
Table Of Contents
- FEATURES
- APPLICATIONS
- CONTENTS
- DESCRIPTION
- DEVICE RATINGS
- ABSOLUTE MAXIMUM RATINGS
- RECOMMENDED OPERATING CONDITIONS
- ELECTROSTATIC DISCHARGE (ESD) PROTECTION
- PACKAGE DISSIPATION RATINGS
- ELECTRICAL CHARACTERISTICS
- TYPICAL CHARACTERISTICS
- DEVICE INFORMATION
- BLOCK DIAGRAM
- APPLICATION INFORMATION
- FUNCTIONAL DESCRIPTION
- Voltage Reference
- Oscillator
- Input Undervoltage Lockout (UVLO) and Startup
- Enable and Timed Turn On of the Outputs
- Output Voltage Sequencing
- Soft Start
- Output Voltage Regulation
- Feedback Loop and Inductor-Capacitor (L-C) Filter Selection
- Inductor-Capacitor (L-C) Selection
- Maximum Output Capacitance
- Minimum Output Capacitance
- Modifying The Feedback Loop
- Example: TPS54386 Buck Converter Operating at 12-V Input, 3.3-V Output and 400-mA(P-P) Ripple Current
- Bootstrap for the N-Channel MOSFET
- Light Load Operation
- SW Node Ringing
- Output Overload Protection
- Operating Near Maximum Duty Cycle
- Dual Supply Operation
- Cascading Supply Operation
- Multiphase Operation
- Bypass and FIltering
- Over-Temperature Protection and Junction Temperature Rise
- Power Derating
- PowerPAD Package
- PCB Layout Guidelines
- FUNCTIONAL DESCRIPTION
- DESIGN EXAMPLES
- ADDITIONAL REFERENCES
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C =
OUTmax
t
SS
V
REF
I
CLx
V-
REF
(1
+ )
R1
R2
V
REF
(1
+ ) ´ T
S
R1
R2
2 V
IN
´ ´ L
R
LOAD
1
+
(1 -
)
(3)
Minimum Output Capacitance
Modifying The Feedback Loop
1
2
3
4
14
13
12
11
PVDD2
BOOT2
SW2
BP
PVDD1
BOOT1
SW1
GND
TPS5438x
5
6
7
10
9
8
SEQ
ILIM2
FB2
EN1
EN2
FB1
R1
OUTPUT1
R2
C1
R3
UDG-07013
C2
TPS54383 , , TPS54386
SLUS774B – AUGUST 2007 – REVISED OCTOBER 2007
Ensure the value of capacitance selected for closed loop stability is compatible with the requirements of Soft
Start .
Within the limits of the internal compensation, there is flexibility in the selection of the inductor and output
capacitor values. A smaller inductor increases ripple current, and raises the resonant frequency, thereby
incerasing the required amount of output capacitance. A smaller capacitor could also be used, increasing the
resonant frequency, and increasing the overall loop bandwidth — perhaps at the expense of adequate phase
margin.
The internal compensation of the TPS54x8x is designed for capacitors with an ESR zero frequency between
20kHz and 60kHz. It is possible, with additional feedback compensation components, to use capacitors with
higher or lower ESR zero frequencies. For either case, the components C1 and R3 (ref.Figure 30 ) are added to
re-compensate the feedback loop for stability. In this configuration a low frequency pole is followed by a higher
frequency zero. The placement of this pole-zero pair is dependent on the type of output capacitor used, and the
desired closed loop frequency response.
Figure 30. Optional Loop Compensation Components
NOTE:
Once the filter and compensation components have been established, laboratory
measurements of the physical design should be performed to confirm converter
stability.
Using High-ESR Output Capacitors
If a high ESR capacitor is used in the output filter, a zero appears in the loop response that could lead to
instability. To compensate, a small R-C series connected network is placed in parallel with the lower voltage
setting divider resistor (Ref Figure 30 ). The values of the components are determined such that a pole is placed
at the same frequency as the ESR zero and a new zero is placed at a frequency location conducive to good loop
stability.
20 Submit Documentation Feedback Copyright © 2007, Texas Instruments Incorporated
Product Folder Link(s): TPS54383 TPS54386