Datasheet

TPS65735
SLVSAI6–JUNE 2011 www.ti.com
Table 3-1. Recommended R
FB1
and R
FB2
Values (for I
Q(FB)
= 5 µA)
Targeted V
BST_OUT
R
FB1
(1)
R
FB2
(1)
8 V 1.3 MΩ 240 kΩ
10 V 1.8 MΩ 240 kΩ
12 V 2.2 MΩ 240 kΩ
14 V 2.4 MΩ 240 kΩ
16 V 3.0 MΩ 240 kΩ
(1) Resistance values given in closest standard value (5% tolerance, E24 grouping).
These resistance values can also be calculated using the following information. To start, it is helpful to
target a quiescent current through the boost feedback network while the device is operating (I
Q(FB)
). When
the boost output voltage and this targeted quiescent current is known, the total feedback network
resistance can be found.
The value for R
FB2
can be found by using the boost feedback pin voltage (V
FB
= 1.2 V, see "Electrical
Characteristics" in Section 2) and I
Q(FB)
in the following equation:
R
FB1
+ R
FB2
= V
BST_OUT
/ I
Q(FB)
R
FB2
= (1.2 V) / I
Q(FB)
To find R
FB1
, simply subtract the R
FB2
from R
FB(TOT)
:
R
FB1
= R
FB(TOT)
- R
FB2
3.3.2 Boost Inductor Selection
The selection of the boost inductor and output capacitor is very important to the performance of the boost
converter. The boost has been designed for optimized operation when a 10 µH inductor is used. Smaller
inductors, down to 4.7 µH, may be used but there will be a slight loss in overall operating efficiency. A few
inductors that have been tested and found to give good performance can be found in the list below:
Recommended 10 µH inductors
• TDK VLS201612ET-100M (10 µH, I
MAX
= 0.53 A, R
DC
= 0.85 Ω)
• Taiyo Yuden CBC2016B100M (10 µH, I
MAX
= 0.41 A, R
DC
= 0.82 Ω)
3.3.3 Boost Capacitor Selection
The recommended minimum value for the capacitor on the boost output, BST_OUT pin, is 4.7 µF. Values
that are larger can be used with the measurable impact being a slight reduction in the boost converter
output voltage ripple while values smaller than this will result in an increased boost output voltage ripple.
Note that the voltage rating of the capacitor should be sized for the maximum expected voltage at the
BST_OUT pin.
3.4 Bypassing Default Push-Button SWITCH Functionality
If the SWITCH pin functionality is not required to power on and off the device because of different system
requirements (when the SWITCH timing requirements of system will be controlled by an external
microcontroller), then the feature can be bypassed. The following diagram shows the connections required
for this configuration, note that INT. I/O refers to an interruptible I/O on the microcontroller.
28 APPLICATION INFORMATION Copyright © 2011, Texas Instruments Incorporated
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