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TPS61040-Q1 Fiches technique(PDF) 10 Page - Texas Instruments |
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TPS61040-Q1 Fiches technique(HTML) 10 Page - Texas Instruments |
10 / 24 page fSmax + Vin min (Vout–Vin) I P L Vout fS I load + 2 I load (Vout–Vin ) Vd) I 2 P L I load max + h I 2 P L fSmax 2 (Vout * Vin) TPS61040-Q1 TPS61041-Q1 SGLS276C – JANUARY 2005 – REVISED APRIL 2012 www.ti.com APPLICATION INFORMATION INDUCTOR SELECTION, MAXIMUM LOAD CURRENT Since the PFM peak current control scheme is inherently stable, the inductor value does not affect the stability of the regulator. The selection of the inductor together with the nominal load current, input and output voltage of the application determines the switching frequency of the converter. Depending on the application, inductor values between 2.2 µH up to 47 µH are recommended. The maximum inductor value is determined by the maximum on time of the switch, typically 6 µs. The peak current limit of 400 mA/250 mA (typically) should be reached within this 6-µs period for proper operation. The inductor value determines the maximum switching frequency of the converter. Therefore, select the inductor value that ensures the maximum switching frequency at the converter maximum load current is not exceeded. The maximum switching frequency is calculated by the following formula: Where: IP = Peak current as described in the previous peak current control section L = Selected inductor value Vinmin = The highest switching frequency occurs at the minimum input voltage (2) If the selected inductor value does not exceed the maximum switching frequency of the converter, the next step is to calculate the switching frequency at the nominal load current using the following formula: Where: IP = Peak current as described in the previous peak current control section L = Selected inductor value Iload = Nominal load current Vd = Rectifier diode forward voltage (typically 0.3 V) (3) A smaller inductor value gives a higher converter switching frequency, but lowers the efficiency. The inductor value has less effect on the maximum available load current and is only of secondary order. The best way to calculate the maximum available load current under certain operating conditions is to estimate the expected converter efficiency at the maximum load current. This number can be taken out of the efficiency graphs shown in Figure 1, Figure 2, Figure 3, and Figure 4. The maximum load current can then be estimated as follows: Where: IP = Peak current as described in the previous peak current control section L = Selected inductor value fSmax = Maximum switching frequency as calculated previously η = Expected converter efficiency. Typically 70% to 85%. (4) 10 Copyright © 2005–2012, Texas Instruments Incorporated |
Numéro de pièce similaire - TPS61040-Q1_15 |
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Description similaire - TPS61040-Q1_15 |
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