12. OUTPUT OVLO
Solve for R OV2 :
SNVS574E – JULY 2008 – REVISED MAY 2013
R OV2 =
V HYSO
23 P A
=
10V
23 P A
= 435 k :
(144)
The closest standard resistor is 432 k ? therefore V HYSO is:
V HYSO = R OV 2 x 23 P A = 432 k : x 23 P A = 9.94V
Solve for R OV1 :
(145)
R OV1 =
1.24V x R OV2
V TURN - OFF - 0.62V
=
1.24V x 432 k :
40V - 0.62V
= 13.6 k :
(146)
The closest standard resistor is 13.7 k ? making V TURN-OFF :
V TURN - OFF =
1.24V x ( 0.5 x R OV1 + R OV2 )
R OV1
V TURN- OFF =
1.24V x ( 0.5 x 13. 7 k : + 432 k : )
13 . 7 k :
= 39.7 V
(147)
The chosen components from step 12 are:
R OV1 = 13.7 k :
R OV2 = 432 k :
(148)
DESIGN #1 Bill of Materials
Qty
1
1
1
1
4
4
1
1
1
1
1
1
1
1
2
1
1
1
1
1
1
1
Part ID
LM3421
C BYP
C CMP
C FS
C IN
C O
C OV
C T
D1
L1
Q1
Q2
R CSH
R FS
R HSP , R HSN
R LIM
R OV1
R OV2
R SNS
R T
R UV1
R UV2
Part Value
Buck-boost controller
2.2 μF X7R 10% 16V
0.33 μF X7R 10% 25V
0.27 μF X7R 10% 25V
4.7 μF X7R 10% 100V
10 μF X7R 10% 50V
47 pF COG/NPO 5% 50V
1000 pF COG/NPO 5% 50V
Schottky 100V 12A
33 μH 20% 6.3A
NMOS 100V 32A
PNP 150V 600 mA
12.4 k ? 1%
10 ? 1%
1.0 k ? 1%
0.04 ? 1% 1W
13.7 k ? 1%
432 k ? 1%
0.1 ? 1% 1W
49.9 k ? 1%
18.2 k ? 1%
130 k ? 1%
Manufacturer
TI
MURATA
MURATA
MURATA
TDK
TDK
AVX
MURATA
VISHAY
COILCRAFT
FAIRCHILD
FAIRCHILD
VISHAY
VISHAY
VISHAY
VISHAY
VISHAY
VISHAY
VISHAY
VISHAY
VISHAY
VISHAY
Part Number
LM3421MH
GRM21BR71C225KA12L
GRM21BR71E334KA01L
GRM21BR71E274KA01L
C5750X7R2A475K
C4532X7R1H106K
08055A470JAT2A
GRM2165C1H102JA01D
12CWQ10FNPBF
MSS1278-333MLB
FDD3682
MMBT5401
CRCW080512K4FKEA
CRCW080510R0FKEA
CRCW08051K00FKEA
WSL2512R0400FEA
CRCW080513K7FKEA
CRCW0805432KFKEA
WSL2512R1000FEA
CRCW080549K9FKEA
CRCW080518K2FKEA
CRCW0805130KFKEA
Copyright ? 2008–2013, Texas Instruments Incorporated
45
Product Folder Links: LM3421 LM3421-Q1 LM3423 LM3423-Q1
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