Electronic Components Datasheet Search |
|
LT1249IN8 Datasheet(PDF) 6 Page - Linear Technology |
|
LT1249IN8 Datasheet(HTML) 6 Page - Linear Technology |
6 / 12 page 6 LT1249 PIN FUNCTIONS VSENSE (Pin 6): This is the inverting input to the voltage amplifier. VCC (Pin 7): This is the supply of the chip. The LT1249 has a very fast gate driver required to fast charge high power MOSFET gate capacitance. High current spikes occur during charging. For good supply bypass, a 0.1 µF ceramic capacitor in parallel with a low ESR electrolytic capacitor, 56 µF or higher is required in close proximity to IC GND. GTDR (Pin 8): The MOSFET gate driver is a 1.5A fast totem pole output. It is clamped at 15V. Capacitive loads like MOSFET gates may cause overshoot. A gate series resis- tor of at least 5 Ω will prevent the overshoot. APPLICATIONS INFORMATION Error Amplifier The error amplifier has a 100dB DC gain and 1.5MHz unity- gain frequency. It is internally clamped at 12V. The nonin- verting input is tied to the 7.5V reference. Current Amplifier The multiplier output current IM flows out of the MOUT pin through the 4k resistor RMOUT and develops the reference signal to the current loop that is controlled by the current amplifier. Current gain is the ratio of RMOUT to line current sense resistor. The current amplifier is a transconductance amplifier. Typical gm is 320µmho and gain is 60dB with no load. The inverting input is internally tied to GND. The noninverting input is tied to the multiplier output. The output is internally clamped at 8V. Output resistance is about 4M; DC loading should be avoided because it will lower the gain and introduce offset voltage at the inputs which becomes a false reference signal to the current loop and can distort line current. Note that in the current averaging operation, high gain at twice the line frequency is necessary to minimize line current distortion. Because CAOUT may need to swing 5V over one line cycle at high line condition, 11mV will be present at the inputs of the current amplifier if gain is rolled off to 450 at 120Hz (1nF in series with 10k at CAOUT). At light load, when (IM)(RMOUT) can be less than 100mV, lower gain will distort the current loop reference signal and line current. If signal gain at the 100kHz switching frequency is too high, the system behaves more like a current mode system and can cause subharmonic oscillation. Therefore, the current amplifier should be compensated to have a gain of less than 15 at 100kHz and more than 300 at 120Hz. Multiplier The multiplier is a current multiplier with high noise immunity in a high power switching environment. The current gain is: IM = (IAC)(IEA2)/(200µA)2, and IEA = (VAOUT – 1.5V)/25k With a square function, because of the lower gain at light power load, system stability is maintained and line current distortion caused by the AC ripple fed back to the error amplifier is minimized. Note that switching ripple on the high impedance lines could get into the multiplier from the IAC pin and cause instability. The LT1249 provides an internal 25k resistor in series with the low impedance multiplier current input so that only a capacitor from the IAC pin to GND is needed to filter out the noise. Maximum multiplier output current is limited to 250 µA. Figure 1 shows the multiplier transfer curves. Figure 1. Multiplier Current IM vs IAC and VAOUT IAC (µA) 0 300 150 0 1249 G04 250 500 VAOUT = 6.5V VAOUT = 6V VAOUT = 5.5V VAOUT = 5V VAOUT = 4.5V VAOUT = 4V VAOUT = 3.5V VAOUT = 3V VAOUT = 2.5V VAOUT = 2V |
Similar Part No. - LT1249IN8 |
|
Similar Description - LT1249IN8 |
|
|
Link URL |
Privacy Policy |
ALLDATASHEET.NET |
Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | 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 |