数据搜索系统,热门电子元器件搜索 |
|
TPS40077PWPR 数据表(PDF) 28 Page - Texas Instruments |
|
|
TPS40077PWPR 数据表(HTML) 28 Page - Texas Instruments |
28 / 43 page www.ti.com P CON + RDS(on) 1 * V OUT V IN * t1 ) t2 f S Iout 2 ) I RIPPLE 2 12 (31) P BD + Vf I OUT t 1 ) t2 f S (32) P GATE + Qg(TOTAL) Vg f S (33) R T + 1 f S 17.82 10*6 * 23 (34) R KFF + 0.131 R T V UVLO(on) * 1.61 10*3 V UVLO(on) 2 ) 1.886 V UVLO * 1.363 * 0.02 R T * 4.87 10*5 R T 2 TPS40077 SLUS714 – JANUARY 2007 where PBD = body diode losses t1 = body diode conduction prior to turnon of channel = 12 ns for PGD t2 = body diode conduction after turnoff of channel = 12 ns for PGD Vf = body diode forward voltage Estimating the body diode losses based on a forward voltage of 1 V gives 0.072 W. The gate losses are unknown at this time, so assume 0.1-W gate losses. This leaves 0.428 W for conduction losses. Using this figure, a target RDS(on) of 5 mΩ was calculated. The Si7336ADP from Vishay was chosen. Using the parameters from its data sheet, the actual expected power losses are calculated. Conduction loss is 0.317 W, body diode loss is 0.072 W, and the gate loss is 0.136W. This totals 0.525 W associated with the rectifier MOSFET. Two other criteria should be verified before finalizing on the rectifier MOSFET. One is the requirement to ensure that predictive gate drive functions correctly. The turnoff delay of the Si7336ADP is 97 ns. The minimum turnoff delay of the Si7860DP is 25 ns. Together these devices meet the 130-ns requirement. Secondly, the ratio between Cgs and Cgd should be greater than 1. The Si7336ADP easily meets this criterion. This helps reduce the risk of dv/dt-induced turnon of the rectifier MOSFET. If this is likely to be a problem, a small resistor may be added in series with the boost capacitor, CBOOST. Component Selection for TPS40077 Timing Resistor, RT The timing resistor is calculated using the following equation. This gives a resistor value of 165 k Ω. The nominal frequency using this resistor is 300 kHz. Feed-Forward and UVLO Resistor, RKFF A resistor connected to the KFF pin of the IC feeds into the ramp generator. This resistor provides current into the ramp generator proportional to the input voltage. The ramp is then adjusted to compensate for different input voltages. This provides the voltage feed-forward feature of the TPS40077. The same resistor also sets the undervoltage lockout point. The input start voltage should be used to calculate a value for RKFF. For this module, the minimum input voltage is 8 V; however, due to tolerances in the IC, a start voltage of 10% less than the minimum input voltage is selected. The start voltage for RKFF calculation is 7.2 V. Using Equation 35, RKFF can be selected. (35) where RKFF and RT are in kΩ. This equation gives an RKFF value of 156 kΩ. The closest lower standard value of 154 kΩ should be selected. This gives a minimum start voltage of 7.1 V. 28 Submit Documentation Feedback |
类似零件编号 - TPS40077PWPR |
|
类似说明 - TPS40077PWPR |
|
|
链接网址 |
隐私政策 |
ALLDATASHEETCN.COM |
ALLDATASHEET是否为您带来帮助? [ DONATE ] |
关于 Alldatasheet | 广告服务 | 联系我们 | 隐私政策 | 链接交换 | 制造商名单 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 |