Os motores de busca de Datasheet de Componentes eletrônicos |
|
ML4790ES Folha de dados(PDF) 8 Page - Micro Linear Corporation |
|
ML4790ES Folha de dados(HTML) 8 Page - Micro Linear Corporation |
8 / 10 page 8 ML4790 The boost capacitor‘s Equivalent Series Resistance (ESR) and Equivalent Series Inductance (ESL), also contribute to the ripple due to the inductor discharge current waveform. Just after the NMOS transistor turns off, the output current ramps quickly to match the peak inductor current. This fast change in current through the boost capacitor‘s ESL causes a high frequency (5ns) spike that can be over 1V in magnitude. After the ESL spike settles, the boost voltage still has a ripple component equal to the inductor discharge current times the ESR. This component will have a sawtooth waveshape and can be calculated using the following formula: ESR V I in BOOST L PEAK ≤Ω ∆ () () (4) For example, a 2.4V input, a 22 µH inductor, and an allowance of 100mV of ripple on the boost capacitor results in a maximum ESR of 200m Ω. Therefore, a boost capacitor with a capacitance of 22 µF or 33µF, an ESR of less than 200m Ω, and an ESL of less than 5nH is a good choice. Tantalum capacitors which meet these requirements can be obtained from the following suppliers: AVX (207) 282-5111 Sprague (207) 324-4140 OUTPUT CAPACITOR The LDO stage output capacitor (C1) is required for stability and to provide a high frequency filter. An output capacitor with a capacitance of 100 µF, an ESR of less than 100m Ω, and an ESL of less than 5nH is a good general purpose choice. INPUT CAPACITOR Unless the input source is a very low impedance battery, it will be necessary to decouple the input with a capacitor with a value of between 47 µF and 100µF. This filtering prevents the input ripple from affecting the ML4790 control circuitry, and it also improves efficiency by reducing I-squared R losses during the charge and discharge cycles of the inductor. Again, a low ESR capacitor (such as tantalum) is recommended. SETTING THE OUTPUT VOLTAGE The adjustable output can be set to any voltage between 2.5V and 5.5V by connecting a resistor divider to the SENSE pin as shown in the block diagram. The resistor values R1 and R2 can be calculated using the following equation: V RR R OUT =× + 02 12 2 . () (5) The value of R2 should be 40kΩ or less to minimize bias current errors. R1 is then found by rearranging the equation: RR VOUT 12 02 1 =× − . (6) It is important to note that the accuracy of these resistors directly affects the accuracy of the output voltage. The SENSE pin threshold variation is ±3%, and the tolerances of R1 and R2 will add to this to determine the total output variation. Input noise may cause output ripple to become excessive due to “pulse grouping,” where the charge-discharge pulses are not evenly spaced in time. In such cases it may be necessary to add a small 500pF to 1000pF ceramic feedback capacitor (CFB) from the VOUT pin to the SENSE pin. |
Nº de peça semelhante - ML4790ES |
|
Descrição semelhante - ML4790ES |
|
|
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 |