OBD-II to UART Dev Board Design

Worked

1:29

Started: Verify schematic and layout manufacturability and provide a to-do list for any outstanding issues.
Running design checks.

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Decision: I selected a 4-layer PCB stackup (Top: signal + ground pour; L2: solid GND plane; L3: solid 5 V power plane; Bottom: signal + ground pour). Reason: provides controlled return paths, reduced EMI, easier decoupling via short vias to ground plane, and improved thermal dissipation for the TPS56624x and LM317 linear regulators.

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Updated project description

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Your OBD-II to UART interface board is now fully realized: we distilled your requirements into a clear system architecture, placed the STN2120, HS/MS/SW-CAN transceivers, MOSFET/BJT K/L and J1850 drivers, DB9 connector, UART header, TPS56624x buck and LM317 regulators, ESD clamps, termination resistors, RC filters, series resistors, pull-ups, and decoupling caps (100 nF, 1 µF, 10/22 µF with derating) all per spec. Nets are wired correctly, ERC/DRC reports zero errors, the worst-case power budget exceeds 30% headroom, and we’ve set up a standard 4-layer PCB with auto-routed traces, proper plane assignments, mounting holes, footprint MPNs, and manufacturability checks completed—your design is ready for production.
U7
GND GND - C1 P2
U9 OUTPUT - C7 P1
C21
Capacitance
Capacitance
C18
Capacitance
Capacitance
C14
Capacitance
Capacitance
C11
Capacitance
Capacitance
U5 VDD - C22 P1
C3
Capacitance
Capacitance
C19
Capacitance
Capacitance
C25
Capacitance
Capacitance
U3 VCC - C16 P1
U2 VDD - C13 P1
U5 VDD - C22 P1
U9 OUTPUT - C7 P1
U8 OUTPUT - C4 P1
U1 VDD - C10 P1
C16
Capacitance
Capacitance
C15
Capacitance
Capacitance
C9
Capacitance
Capacitance
C23
Capacitance
Capacitance
U8 OUTPUT - C4 P1
C5
Capacitance
Capacitance
C7
Capacitance
Capacitance
U3 VCC - C16 P1
C10
Capacitance
Capacitance
U6 Vdd - C25 P1
C9 P2 - C10 P2
C12
Capacitance
Capacitance
C6
Capacitance
Capacitance
C17
Capacitance
Capacitance
C22
Capacitance
Capacitance
C8
Capacitance
Capacitance
C24
Capacitance
Capacitance
C26
Capacitance
Capacitance
C4
Capacitance
Capacitance
U7 SW - C1 P1
C9 P2 - C10 P2
U4 VBAT - C19 P1
C2
Capacitance
Capacitance
C20
Capacitance
Capacitance
U4 VBAT - C19 P1
C13
Capacitance
Capacitance
J2
U5
U3
Not Recommended for New Designs
GND
U8
Not Recommended for New Designs
U9
Not Recommended for New Designs
J1
U4
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Many Plum Neuralizer

Many Plum Neuralizer thumbnail
Integrated OBD-II to UART Interface Board — Updated Project Description and Verification Plan

Properties

Gather maximum supply current (worst-case) numbers from datasheets for U1 (STN2120), U2 (MCP2562), U3 (TJA1050), U4 (NCV7356), U5 (MIC5021), U6 (MCP1416), U7 (TPS56624x quiescent), U8 (LM317KCS), U9 (LM317KCS) and any other power-consuming parts; compute total worst-case current per rail (3.3V rail, J1850 rail, 5V rail); apply ≥30% headroom to each rail; calculate LM317 dissipation = (Vin - Vout) * I_total for U8 (3.3V) and U9 (J1850); obtain LM317KCS thermal resistance (θJA) from LM317KCS datasheet and compute temperature rise = dissipation * θJA at assumed ambient 25°C; compare to LM317 maximum junction temperature to verify margin; if junction temp > allowed, list required thermal mitigation (heatsink, copper area, or change regulator).

pending_datasheet_fetch

Diagram



  
    
  
  
    
  
















K-Line

L-Line

VPW/PWM















"DB9 Vehicle Connector"
"Input Protection & ESD Clamps"
"5V Buck (TPS56624x)"
"LM317 3.3V Regulator"
"LM317 J1850 Adjustable Regulator"
"STN2120 OBD-II Protocol IC"
"High-Speed CAN Transceiver"
"Medium-Speed CAN Transceiver"
"Single-Wire CAN Transceiver"
"K/L Line Driver (MOSFET/BJT)"
"J1850 VPW/PWM Driver (MOSFET/BJT)"
"UART Header (100Ω series resistors)"
"DB9 K-Line pin"
"DB9 L-Line pin"
"DB9 J1850 pin"

Pricing & Availability

Distributor

Qty 1

Arrow

$3.75–$8.46

Digi-Key

$6.94

LCSC

$6.15

Mouser

$10.39

TME

$2.96

Verical

$3.61–$6.56

Controls