Electronic Components Datasheet Search |
|
LT1307 Datasheet(PDF) 9 Page - Linear Technology |
|
LT1307 Datasheet(HTML) 9 Page - Linear Technology |
9 / 20 page 9 LT1307/LT1307B 1307fa quite evident, as is this particular device’s 575kHz switch- ing frequency (nominal switching frequency is 600kHz). Note, however, the absence of significant energy at 455kHz. Figure 7’s plot reduces the frequency span from 255kHz to 655kHz with a 455kHz center. Burst Mode low frequency ripple creates sidebands around the 575kHz switching fundamental. These sidebands have low signal amplitude at 455kHz, measuring – 55dBmVRMS. As load current is further reduced, the Burst Mode frequency decreases. This spaces the sidebands around the switching fre- quency closer together, moving spectral energy further Trace B. Similarly, Figure 4 details the two circuits with a load step from 5mA to 45mA with a 1.5V input. The LT1307B also can be used in lower current applica- tions where a clean, low ripple output is needed. Figure 5 details transient response of a single cell to 3.3V con- verter, using an inductor value of 100 µH. This high induc- tance minimizes ripple current, allowing the LT1307B to regulate without skipping cycles. As the load current is stepped from 5mA to 10mA, the output voltage responds cleanly. Note that the VC pin loop compensation has been made more conservative (increased C, decreased R). Figure 5. Increasing L to 100 µH, Along with RC = 36k, CC = 20nF and COUT = 10µF, Low Noise Performance of LT1307B Can Be Realized at Light Loads of 5mA to 10mA 10mA 5mA IL VIN = 1.25V 1ms/DIV 1307 F05 VOUT = 3.3V IL 20mA/DIV VOUT 100mV/DIV AC COUPLED At light loads, the LT1307B will begin to skip alternate cycles. The load point at which this occurs can be de- creased by increasing the inductor value. However, output ripple will continue to be significantly less than the LT1307 output ripple. Further, the LT1307B can be forced into micropower mode, where IQ falls from 1mA to 50µA by pulling down VC to 0.3V or less externally. DC/DC CONVERTER NOISE CONSIDERATIONS Switching regulator noise is a significant concern in many communications systems. The LT1307 is designed to keep noise energy out of the sensitive 455kHz band at all load levels while consuming only 60 µW to 100µW at no load. At light load levels, the device is in Burst Mode, causing low frequency ripple to appear at the output. Figure 6 details spectral noise directly at the output of Figure 1’s circuit in a 1kHz to 1MHz bandwidth. The converter supplies a 5mA load from a 1.25V input. The Burst Mode fundamental at 5.1kHz and its harmonics are FREQUENCY (kHz) 1 40 30 20 10 0 –10 –20 –30 –40 –50 –60 10 100 1000 1307 F06 RBW = 100Hz Figure 6. Spectral Noise Plot of 3.3V Converter Delivering 5mA Load. Burst Mode Fundamental at 5.1kHz is 23dBmVRMS or 14mVRMS FREQUENCY (kHz) 255 –20 –25 –30 –35 –40 –45 –50 –55 –60 –65 –70 455 1307 F07 655 RBW = 100Hz Figure 7. Span Centered at 455kHz Shows – 55dBmVRMS (1.8 µVRMS) at 455kHz. Burst Mode Creates Sidebands 5.1kHz Apart Around the Switching Frequency Fundamental of 575kHz APPLICATIO S I FOR ATIO |
Similar Part No. - LT1307_15 |
|
Similar Description - LT1307_15 |
|
|
Link URL |
Privacy Policy |
ALLDATASHEET.COM |
Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | Datasheet Upload | Contact us | Privacy Policy | Link Exchange | Manufacturer List 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 |