Datasheet
R5 + R6
ƪ
V
out
V
FB
* 1
ƫ
+ R6 ƪ
V
out
1.214
* 1ƫ
V
out
+ 1.214
ƪ
1 )
R5
R6
ƫ
TPS65140, TPS65141
TPS65145
www.ti.com
SLVS497E –SEPTEMBER 2003–REVISED NOVEMBER 2012
Voltage doubler:
V
O
3
max
= 2 x V
O
1 - (2 V
D
+ 2 x I
O
x (2 x r
DS(on)Q5
+ r
DS(on)Q3
+ r
DS(on)Q4
+ X
C1
))
Voltage tripler:
V
O
3
max
= 3 x V
O
- (3 x V
D
+ 2 x I
O
x (3 x r
DS(on)Q5
+ r
DS(on)Q3
+ r
DS(on)Q4
+ X
C1
+ X
C2
))
The output voltage is set by the external resistor divider and is calculated as:
Linear Regulator Controller
The TPS6514x includes a linear regulator controller to generate a 3.3-V rail when the system is powered from a
5-V supply. Because an external npn transistor is required, the input voltage of the TPS6514x applied to VIN
needs to be higher than the output voltage of the regulator. To provide a minimum base drive current of 13.5 mA,
a minimum internal voltage drop of 500 mV from V
in
to V
base
is required. This can be translated into a minimum
input voltage on VIN for a certain output voltage as the following calculation shows:
V
I(min)
= V
O
4 + V
BE
+ 0.5 V
The base drive current together with the h
FE
of the external transistor determines the possible output current.
Using a standard npn transistor like the BCP68 allows an output current of 1 A and using the BCP54 allows a
load current of 337 mA for an input voltage of 5 V. Other transistors can be used as well, depending on the
required output current, power dissipation, and PCB space. The device is stable with a 4.7-μF ceramic output
capacitor. Larger output capacitor values can be used to improve the load transient response when higher load
currents are required.
Thermal Information
An influential component of the thermal performance of a package is board design. To take full advantage of the
heat dissipation abilities of the PowerPAD or QFN package with exposed thermal die, a board that acts similar to
a heatsink and allows for the use of an exposed (and solderable) deep downset pad should be used. For further
information. see Texas Instrumens application notes (SLMA002) PowerPAD Thermally Enhanced Package, and
(SLMA004) Power Pad Made Easy. For the QFN package, see the application report (SLUA271) QFN/SON PCB
Attachement. Especially for the QFN package it is required to solder down the Thermal Pad to achieve the
required thermal resistance.
Layout Considerations
For all switching power supplies, the layout is an important step in the design, especially at high-peak currents
and switching frequencies. If the layout is not carefully designed, the regulator might show stability and EMI
problems. Therefore, the traces carrying high-switching currents should be routed first using wide and short
traces. The input filter capacitor should be placed as close as possible to the input pin VIN of the IC. See the
evaluation module (EVM) for a layout example.
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Product Folder Links: TPS65140 TPS65141 TPS65145