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TPS61236 Datasheet(PDF) 17 Page - Texas Instruments

No. de Pieza. TPS61236
Descripción  TPS6123x 8-A Valley Current Synchronous Boost Converters with Constant Current Output Feature
Descarga  38 Pages
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Fabricante  TI1 [Texas Instruments]
Página de inicio  http://www.ti.com
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TPS61236 Datasheet(HTML) 17 Page - Texas Instruments

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TPS61235P, TPS61236P
www.ti.com
SLVSCK4A – SEPTEMBER 2015 – REVISED MAY 2016
Product Folder Links: TPS61235P TPS61236P
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Copyright © 2015–2016, Texas Instruments Incorporated
(1)
See Third-party Products Disclaimer
9.2.1.2 Detailed Design Procedure
The following sections describe the selection process of the external components. The following table summaries
the final component selections.
Table 2. List of Components for TPS61236P 5-V Output with 3-A Constant Output Current Application
REFERENCE
DESCRIPTION
MANUFACTURER(1)
L1
1.0 μH, Power Inductor, XAL7030
Coilcraft
C1
10 μF 6.3 V, 0603, X5R ceramic, GRM188R60J106ME84
Murata
C2
3 × 22 μF 10 V, 0805, X5R ceramic, GRM21BR61A226ME44
Murata
C3
10 nF, 50 V, 0603, X5R ceramic, GRM188R61H103KA01D
Murata
C4
1 µF, 6.3 V, 0402, X5R ceramic, GRM152R60J105ME15
Murata
R1
1 MΩ, Resistor, Chip, 1/10W, 1%
Rohm
R2
332 kΩ, Resistor, Chip, 1/10W, 0.5%
Rohm
R3
41.2 kΩ, Resistor, Chip, 1/10W, 0.5%
Rohm
R4
1 MΩ, Resistor, Chip, 1/10W, 1%
Rohm
R5
1 MΩ, Resistor, Chip, 1/10W, 1%
Rohm
9.2.1.2.1
Programming the Output Voltage
The TPS61236P's output voltage needs to be programmed via an external voltage divider at the FB pin, as
shown in Figure 16.
By selecting R1 and R2, the output voltage is programmed to the desired value. When the output voltage is
regulated, the typical voltage at the FB pin is VFB. The following equation can be used to calculate R1 and R2.
(6)
For the best accuracy, the current following through R2 should be 100 times larger than FB pin leakage current.
Changing R2 towards a lower value increases the robustness against noise injection. Changing R2 towards
higher values reduces the FB divider current for achieving the highest efficiency at low load currents.
For the fixed output voltage version, TPS61235P, the FB pin must be tied to the output directly.
In this example, 1-MΩ and 332-kΩ resistors are selected for R1 and R2. High accuracy like 0.5% resistors are
recommended for better output voltage accuracy.
9.2.1.2.2
Program the Constant Output Current
The TPS6123x's constant output current can be programmed via an external resistor RCC at the CC pin.
Because the TPS6123x has an internal current limit function to protect the IC from over load situations, a user
should make sure the constant output current is set within the device's maximum load capability. If the constant
current is set too high, the output current will be limited by internal protection circuitry and cannot reach the set
value.
The maximum output capability is determined by the input to output voltage ratio and the internal current limit
ILIM. Refer to Equation 3, Equation 4, and Equation 5 for the maximum output current calculation. The minimum
input voltage, minimum current limit value, and maximum switching frequency value shall be used for the worst
case calculation.
In this example, the minimum input voltage is 3-V and output voltage is 5-V. The efficiency η can be estimated as
85% for the worst case condition. By checking the specification table, the minimum ILIM value is 6.5-A, and
maximum switching frequency fSW is 1250-kHz, so the calculation result of the maximum output current under the
worse case condition is 3.6-A.
After calculation, the 3-A constant current target is within the maximum output current range, so the user can set
it. Equation 2 can be used to select RCC (R3 in Figure 16). In this example, the calculation result of R3 is 41.47-
kΩ. A 1% accuracy 41.2-kΩ resistor is selected. By using it, the constant output current can be regulated at 3-A
typically.


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