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SC4525ASETRT датащи(PDF) 14 Page - Semtech Corporation |
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SC4525ASETRT датащи(HTML) 14 Page - Semtech Corporation |
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14 / 19 page ![]() (3) Place the compensator zero, F Z, between 0% and 20% of the crossover frequency, F C. (4) Use the compensator pole, F P, to cancel the ESR zero, F Z. (5) Then, the parameters of the compensation network can be calculated by where g m=0.28mA/V is the EA gain of the SC4525A. Example: Determine the voltage compensator for an 800kHz, 2V to 3.3V/3A converter with 47uF ceramic output capacitor. Choose a loop gain crossover frequency of 80kHz, and place voltage compensator zero and pole at F Z=6kHz (20% of F C), and FP=600kHz. From Equation (9), the required compensator gain at F C is Then the compensator parameters are Select R 7=3.4k, C5=0.33nF, and C8=0pF for the design. Compensator parameters for various typical applications are listed in Table 5. A MathCAD program is also available upon request for detailed calculation of the compensator parameters. CESAT D IN D O V V V V V D − + + = − = 1 V 0 . 1 V R R O 6 4 1 SW D O L L F ) D 1 ( ) V V ( I ⋅ − ⋅ + = D SW O D O 1 F I % 20 ) D 1 ( ) V V ( L ⋅ ⋅ − ⋅ + = ) D 1 ( D I I O CIN _ RMS − ⋅ ⋅ = ⋅ ⋅ + ⋅ D = D O SW L O C F 8 1 ESR I V SW IN O IN F V 4 I C ⋅ D ⋅ > , R G R G S CA PWM ⋅ ≈ ) / s Q / s 1 () / s 1 ( ) C R s 1 ( G V V 2 n 2 n p O ESR PWM c o ω + ω + ω + + = 7 1 Z 5 R F 2 1 C π = 7 1 P 8 R F 2 1 C π = , C R 1 O p ≈ ω , C R 1 O ESR Z = ω k 3 . 22 10 28 . 0 10 R 3 7 20 9 . 15 = ⋅ = − nF 45 . 0 10 1 . 22 10 16 2 1 C 3 3 5 = ⋅ ⋅ ⋅ ⋅ π = pF 12 10 1 . 22 10 600 2 1 C 3 3 8 = ⋅ ⋅ ⋅ ⋅ π = ⋅ π ⋅ ⋅ − = O FB O C S CA C V V C F 2 1 R G 1 log 20 A dB 9 . 15 3 . 3 0 . 1 10 22 10 80 2 1 10 1 . 6 28 1 log 20 A 6 3 3 C = ⋅ ⋅ ⋅ ⋅ ⋅ π ⋅ ⋅ ⋅ ⋅ − = − − m 7 g 10 R 20 C A = CESAT D IN D O V V V V V D − + + = − = 1 V 0 . 1 V R R O 6 4 1 SW D O L L F ) D 1 ( ) V V ( I ⋅ − ⋅ + = D SW O D O 1 F I % 20 ) D 1 ( ) V V ( L ⋅ ⋅ − ⋅ + = ) D 1 ( D I I O CIN _ RMS − ⋅ ⋅ = ⋅ ⋅ + ⋅ D = D O SW L O C F 8 1 ESR I V SW IN O IN F V 4 I C ⋅ D ⋅ > , R G R G S CA PWM ⋅ ≈ ) / s Q / s 1 () / s 1 ( ) C R s 1 ( G V V 2 n 2 n p O ESR PWM c o ω + ω + ω + + = 7 1 Z 5 R F 2 1 C π = 7 1 P 8 R F 2 1 C π = , C R 1 O p ≈ ω , C R 1 O ESR Z = ω k 3 . 22 10 28 . 0 10 R 3 7 20 9 . 15 = ⋅ = − nF 45 . 0 10 1 . 22 10 16 2 1 C 3 3 5 = ⋅ ⋅ ⋅ ⋅ π = pF 12 10 1 . 22 10 600 2 1 C 3 3 8 = ⋅ ⋅ ⋅ ⋅ π = ⋅ π ⋅ ⋅ − = O FB O C S CA C V V C F 2 1 R G 1 log 20 A dB 9 . 15 3 . 3 0 . 1 10 22 10 80 2 1 10 1 . 6 28 1 log 20 A 6 3 3 C = ⋅ ⋅ ⋅ ⋅ ⋅ π ⋅ ⋅ ⋅ ⋅ − = − − m 7 g 10 R 20 C A = CESAT D IN D O V V V V V D − + + = − = 1 V 0 . 1 V R R O 6 4 1 SW D O L L F ) D 1 ( ) V V ( I ⋅ − ⋅ + = D ) D 1 ( D I I O CIN _ RMS − ⋅ ⋅ = ⋅ ⋅ + ⋅ D = D O SW L O C F 8 1 ESR I V SW IN O IN F V 4 I C ⋅ D ⋅ > , R G R G S CA PWM ⋅ ≈ ) / s Q / s 1 () / s 1 ( ) C R s 1 ( G V V 2 n 2 n p O ESR PWM c o ω + ω + ω + + = 7 1 Z 5 R F 2 1 C π = 7 1 P 8 R F 2 1 C π = , C R 1 O p ≈ ω , C R 1 O ESR Z = ω ⋅ π ⋅ ⋅ − = O FB O C S CA C V V C F 2 1 R G 1 log 20 A m 7 g 10 R 20 C A = SW O D O 1 F I % 35 ) D 1 ( ) V V ( L ⋅ ⋅ − ⋅ + = dB 19 3 . 3 0 . 1 10 47 10 80 2 1 10 1 . 4 28 1 log 20 A 6 3 3 C = ⋅ ⋅ ⋅ ⋅ ⋅ π ⋅ ⋅ ⋅ ⋅ − = − − k 8 . 31 10 28 . 0 10 R 3 7 20 19 = ⋅ = − nF 31 . 0 10 4 . 31 10 16 2 1 C 3 3 5 = ⋅ ⋅ ⋅ ⋅ π = pF 5 . 8 10 4 . 31 10 600 2 1 C 3 3 8 = ⋅ ⋅ ⋅ ⋅ π = CESAT D IN D O V V V V V D − + + = − = 1 V 0 . 1 V R R O 6 4 1 SW D O L L F ) D 1 ( ) V V ( I ⋅ − ⋅ + = D ) D 1 ( D I I O CIN _ RMS − ⋅ ⋅ = ⋅ ⋅ + ⋅ D = D O SW L O C F 8 1 ESR I V SW IN O IN F V 4 I C ⋅ D ⋅ > , R G R G S CA PWM ⋅ ≈ ) / s Q / s 1 () / s 1 ( ) C R s 1 ( G V V 2 n 2 n p O ESR PWM c o ω + ω + ω + + = 7 1 Z 5 R F 2 1 C π = 7 1 P 8 R F 2 1 C π = , C R 1 O p ≈ ω , C R 1 O ESR Z = ω ⋅ π ⋅ ⋅ − = O FB O C S CA C V V C F 2 1 R G 1 log 20 A m 7 g 10 R 20 C A = SW O D O 1 F I % 35 ) D 1 ( ) V V ( L ⋅ ⋅ − ⋅ + = dB 19 3 . 3 0 . 1 10 47 10 80 2 1 10 1 . 4 28 1 log 20 A 6 3 3 C = ⋅ ⋅ ⋅ ⋅ ⋅ π ⋅ ⋅ ⋅ ⋅ − = − − k 8 . 31 10 28 . 0 10 R 3 7 20 19 = ⋅ = − nF 31 . 0 10 4 . 31 10 16 2 1 C 3 3 5 = ⋅ ⋅ ⋅ ⋅ π = pF 5 . 8 10 4 . 31 10 600 2 1 C 3 3 8 = ⋅ ⋅ ⋅ ⋅ π = CESAT D IN D O V V V V V D − + + = − = 1 V 0 . 1 V R R O 6 4 1 SW D O L L F ) D 1 ( ) V V ( I ⋅ − ⋅ + = D ) D 1 ( D I I O CIN _ RMS − ⋅ ⋅ = ⋅ ⋅ + ⋅ D = D O SW L O C F 8 1 ESR I V SW IN O IN F V 4 I C ⋅ D ⋅ > , R G R G S CA PWM ⋅ ≈ ) / s Q / s 1 () / s 1 ( ) C R s 1 ( G V V 2 n 2 n p O ESR PWM c o ω + ω + ω + + = 7 1 Z 5 R F 2 1 C π = 7 1 P 8 R F 2 1 C π = , C R 1 O p ≈ ω , C R 1 O ESR Z = ω ⋅ π ⋅ ⋅ − = O FB O C S CA C V V C F 2 1 R G 1 log 20 A m 7 g 10 R 20 C A = SW O D O 1 F I % 35 ) D 1 ( ) V V ( L ⋅ ⋅ − ⋅ + = dB 19 3 . 3 0 . 1 10 47 10 80 2 1 10 1 . 4 28 1 log 20 A 6 3 3 C = ⋅ ⋅ ⋅ ⋅ ⋅ π ⋅ ⋅ ⋅ ⋅ − = − − k 8 . 31 10 28 . 0 10 R 3 7 20 19 = ⋅ = − nF 31 . 0 10 4 . 31 10 16 2 1 C 3 3 5 = ⋅ ⋅ ⋅ ⋅ π = pF 5 . 8 10 4 . 31 10 600 2 1 C 3 3 8 = ⋅ ⋅ ⋅ ⋅ π = CESAT D IN D O V V V V V D − + + = − = 1 V 0 . 1 V R R O 6 4 1 SW D O L L F ) D 1 ( ) V V ( I ⋅ − ⋅ + = D ) D 1 ( D I I O CIN _ RMS − ⋅ ⋅ = ⋅ ⋅ + ⋅ D = D O SW L O C F 8 1 ESR I V SW IN O IN F V 4 I C ⋅ D ⋅ > , R G R G S CA PWM ⋅ ≈ ) / s Q / s 1 () / s 1 ( ) C R s 1 ( G V V 2 n 2 n p O ESR PWM c o ω + ω + ω + + = 7 1 Z 5 R F 2 1 C π = 7 1 P 8 R F 2 1 C π = , C R 1 O p ≈ ω , C R 1 O ESR Z = ω ⋅ π ⋅ ⋅ − = O FB O C S CA C V V C F 2 1 R G 1 log 20 A m 7 g 10 R 20 C A = SW O D O 1 F I % 35 ) D 1 ( ) V V ( L ⋅ ⋅ − ⋅ + = dB 19 3 . 3 0 . 1 10 47 10 80 2 1 10 1 . 4 28 1 log 20 A 6 3 3 C = ⋅ ⋅ ⋅ ⋅ ⋅ π ⋅ ⋅ ⋅ ⋅ − = − − k 8 . 31 10 28 . 0 10 R 3 7 20 19 = ⋅ = − nF 31 . 0 10 4 . 31 10 16 2 1 C 3 3 5 = ⋅ ⋅ ⋅ ⋅ π = pF 5 . 8 10 4 . 31 10 600 2 1 C 3 3 8 = ⋅ ⋅ ⋅ ⋅ π = Thermal Considerations For the power transistor inside the SC4525A, the conduction loss P C, the switching loss PSW, and bootstrap circuit loss P BST, can be estimated as follows: (0) whereV BST is the BST supply voltage and tS is the equivalent switching time of the NPN transistor (see Table 4). Table 4. Typical switching time In addition, the quiescent current loss is () The total power loss of the SC4525A is therefore (2) The temperature rise of the SC4525A is the product of the total power dissipation (Equation (2)) and q JA (36 o C/W), which is the thermal impedance from junction to ambient for the SOIC-8 EDP package. It is not recommended to operate the SC4525A above 25oC junction temperature. In the applications with high input voltage and high output current, the switching frequency may need to be reduced to meet the thermal requirement. O CESAT C I V D P ⋅ ⋅ = 40 I V D P O BST BST ⋅ ⋅ = DC 2 O IND R I ) 3 . 1 ~ 1 . 1 ( P ⋅ ⋅ = O D D I V ) D 1 ( P ⋅ ⋅ − = SW O IN S SW F I V t 2 1 P ⋅ ⋅ ⋅ ⋅ = Q BST SW C TOTAL P P P P P + + + = mA 2 V P IN Q ⋅ = O CESAT C I V D P ⋅ ⋅ = 40 I V D P O BST BST ⋅ ⋅ = DC 2 O IND R I ) 3 . 1 ~ 1 . 1 ( P ⋅ ⋅ = O D D I V ) D 1 ( P ⋅ ⋅ − = SW O IN S SW F I V t 2 1 P ⋅ ⋅ ⋅ ⋅ = Q BST SW C TOTAL P P P P P + + + = mA 2 V P IN Q ⋅ = 1A 2A 3A 12V 12.5ns 15.3ns 18ns 24V 22ns 25ns 28ns 28V 25.3ns 28ns 31ns Load Current Input Voltage 1A 2A 3A 12V 12.5ns 15.3ns 18ns 24V 22ns 25ns 28ns 28V 25.3ns 28ns 31ns Load Current Input Voltage O CESAT C I V D P ⋅ ⋅ = 40 I V D P O BST BST ⋅ ⋅ = DC 2 O IND R I ) 3 . 1 ~ 1 . 1 ( P ⋅ ⋅ = O D D I V ) D 1 ( P ⋅ ⋅ − = SW O IN S SW F I V t 2 1 P ⋅ ⋅ ⋅ ⋅ = Q BST SW C TOTAL P P P P P + + + = mA 2 V P IN Q ⋅ = O CESAT C I V D P ⋅ ⋅ = 40 I V D P O BST BST ⋅ ⋅ = DC 2 O IND R I ) 3 . 1 ~ 1 . 1 ( P ⋅ ⋅ = O D D I V ) D 1 ( P ⋅ ⋅ − = SW O IN S SW F I V t 2 1 P ⋅ ⋅ ⋅ ⋅ = Q BST SW C TOTAL P P P P P + + + = mA 2 V P IN Q ⋅ = O CESAT C I V D P ⋅ ⋅ = 40 I V D P O BST BST ⋅ ⋅ = DC 2 O IND R I ) 3 . 1 ~ 1 . 1 ( P ⋅ ⋅ = O D D I V ) D 1 ( P ⋅ ⋅ − = SW O IN S SW F I V t 2 1 P ⋅ ⋅ ⋅ ⋅ = Q BST SW C TOTAL P P P P P + + + = mA 2 V P IN Q ⋅ = O CESAT C I V D P ⋅ ⋅ = 40 I V D P O BST BST ⋅ ⋅ = DC 2 O IND R I ) 3 . 1 ~ 1 . 1 ( P ⋅ ⋅ = O D D I V ) D 1 ( P ⋅ ⋅ − = SW O IN S SW F I V t 2 1 P ⋅ ⋅ ⋅ ⋅ = Q BST SW C TOTAL P P P P P + + + = mA 2 V P IN Q ⋅ = SC4525A 4 Applications Information (Cont.) |
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