Os motores de busca de Datasheet de Componentes eletrônicos |
|
BD9778HFP Folha de dados(PDF) 9 Page - Rohm |
|
BD9778HFP Folha de dados(HTML) 9 Page - Rohm |
9 / 17 page 9/16 Technical Note Description of external components Design procedure Calculation example Vo = Output voltage, Vin (Max.) = Maximum input voltage Io (Max.) = Maximum load current, f = Oscillation frequency 1. Setting or output voltage Output voltage can be obtained by the formula shown below. VO=1 x (1+R1/R2) Use the formula to select the R1 and R2. Furthermore, set the R2 to 30 kΩ or less. Select the current passing through the R1 and R2 to be small enough for the output current. 2. Selection of coil (L) The value of the coil can be obtained by the formula shown below: L=(VIN-VO) x VO / (VIN x f x ∆IO) ∆IO: Output ripple current f = Operating frequency ∆Io should typically be approximately 20 to 30% of Io. 3. Selection of output capacitor (Co) The output capacitor can be determined according to the output ripple voltage ∆Vo (p-p) required. Obtain the required ESR value by the formula shown below and then select the capacitance. When VIN = 13.2 V, Vo = 5 V, Io = 2 A, and f = 100 kHz, L=(13.2-5) x 5/13.2 x 1/100k x 1/(2 x 0.3) =51.8µH 47µ VIN=13.2V, Vo=5V, L=100µH, f=100kHz ∆IL=(13.2-5) x 5/(100 x 10-6 x 100 x 103 x 13.2) 0.31 When Vo = 5 V and R2 = 10 kΩ, 5=1 x (1+R1/10kΩ) R1=40kΩ L=47 µH Fig.30 VIN RT SS SW INV FB GND CT Cin Di CO + VO VIN CC RC C L R1 R2 RT CSS 3.5m x (ILimit-Io(Max)) Vo CMax= CMax=3.5m x (2-1)/5 =700µ ∆IL=0.31A CMax=700µF If this coil is not set to the optimum value, normal (continuous) oscillation may not be achieved. Furthermore, set the value of the coil with an adequate margin so that the peak current passing through the coil will not exceed the rated current of the coil. ILimit:2A(BD9778F/HFP,BD9001F), 4A(BD9781HFP) If this capacitance is not optimum, faulty startup may result. ( 3.5m is soft start time(min.)) When ILimit: 2 A, Io (Max) = 1 A, and Vo = 5V, ∆IL=(VIN-VO) x VO/(L x f x VIN) ∆Vpp=∆IL x ESR+(∆IL x Vo)/(2 x Co x f x VIN) Set the rating of the capacitor with an adequate margin to the output voltage. Also, set the maximum allowable ripple current with an adequate margin to ∆IL. Furthermore, the output rise time should be shorter than the soft start time. Select the output capacitor having a value smaller than that obtained by the formula shown below. 2010.02 - Rev. B www.rohm.com © 2010 ROHM Co., Ltd. All rights reserved. BD9778F, BD9778HFP, BD9001F, BD9781HFP |
Nº de peça semelhante - BD9778HFP |
|
Descrição semelhante - BD9778HFP |
|
|
Ligação URL |
Privacy Policy |
ALLDATASHEETPT.COM |
ALLDATASHEET é útil para você? [ DONATE ] |
Sobre Alldatasheet | Publicidade | Contato conosco | Privacy Policy | roca de Link | Lista de Fabricantes All Rights Reserved©Alldatasheet.com |
Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
Family Site : ic2ic.com |
icmetro.com |