L7805ABD2T-TR - +5V Linear Regulator

Fixed positive voltage regulator providing stable +5V output in compact TO-263-2 (D2PAK) surface-mount package with excellent thermal performance.

• View on JLCPCB: C86206

• Download Datasheet (PDF)

Overview

The L7805ABD2T-TR is a three-terminal positive voltage regulator in TO-263-2 (D2PAK) package, designed to provide a fixed +5V output from a higher input voltage. This component serves as the final stage in the +5V power rail, converting the +7.5V DC-DC output to a clean, low-noise +5V suitable for modular synthesizer digital circuits and control voltage applications.

Key Specifications

Pin Configuration

         TO-263-2 (D2PAK) Package
              Top View

         ┌──────────────┐
         │              │
         │   L7805A     │
         │   BD2T-TR    │
         │              │
         │              │
         └──┬───────┬───┘
            │       │
          PIN1    PIN2
          INPUT    GND
         (+7.5V) (Common)

              TAB
           (OUTPUT)
            (+5V)

         Side View

         ┌──────────────┐
         │   Component  │ ← Surface mount IC
         └──┬───────┬───┘
            │       │
          PIN1    PIN2

    ════════════════════  ← Metal tab (OUTPUT)
                            soldered to PCB pad

Pin Descriptions

Note: Unlike TO-220 package, the TO-263-2 has the OUTPUT on the metal tab, not on pin 3.

Application Circuit

+7.5V (from DC-DC) ───┬─── C12: 470nF ───┬─── U7: L7805ABD2T ───┬─── C15: 100nF ───┬─→ +5V OUT
                      │                  │                      │                  │
                      │                  │    ┌──────────┐      │                  │
                      │                  └────│1  INPUT  │      │                  │
                      │                       │          │      │                  │
                      │                    ┌──│2   GND   │      │                  │
                      │                    │  │          │      │                  │
                      │                    │  │   TAB ───┴──────┴──────────────────┤
                      │                    │  └──────────┘                         │
                      │                    │     (OUTPUT)                          │
                      └─── C19: 470µF ─────┼─────────┬─── C20: 470µF ──────────────┤
                           (Input)         │         │    (Output)                 │
                                           │         │                             │
                                          GND       GND                            │
                                                                                   │
                                        ┌──────────────────────────────────────────┘
                                        │
                                  ┌─────┴─────┐
                                  │   LED3    │ Blue Status LED
                                  │  (Blue)   │ via R8: 1kΩ
                                  └─────┬─────┘
                                        │
                                       GND

Component Values

Input Capacitors

Output Capacitors

Status LED Circuit

Design Considerations

Input Voltage Requirements

The L7805ABD2T requires a minimum input voltage of approximately 7V for proper regulation (5V output + 2V dropout). In this design:

• Input voltage: +7.5V from LM2596S DC-DC converter

• Dropout margin: 7.5V - 5V = 2.5V

• Status: ✅ Excellent - well above minimum dropout voltage

The 2.5V margin provides:

1. Stable regulation across load variations

2. Tolerance for input voltage ripple

3. Reduced power dissipation compared to higher input voltages

4. Optimal efficiency for the linear regulator stage

Thermal Management

Power dissipation calculation:

P = (VIN - VOUT) × IOUT
P = (7.5V - 5V) × 0.5A
P = 2.5V × 0.5A
P = 1.25W

Temperature rise without additional heatsinking:

ΔT = P × θJA
ΔT = 1.25W × 35°C/W
ΔT = 43.75°C

At 25°C ambient, junction temperature = 68.75°C (well within 125°C maximum).

Thermal performance advantages of TO-263-2:

• Lower θJA than TO-220 (35°C/W vs 50°C/W)

• Large metal tab provides excellent heat spreading

• Direct thermal contact with PCB copper pour

• No additional heatsink required for this application

PCB copper area recommendations:

• Minimum: 2 cm² copper pour connected to tab

• Recommended: 5 cm² copper pour for better margin

• Thermal vias: 6-10 vias (0.3mm) under tab to bottom layer

Capacitor Placement

Critical for stability and noise rejection:

1. C12 (470nF ceramic): Place within 5mm of pin 1

• Purpose: Suppress high-frequency noise from DC-DC stage

• Type: X7R or better (maintains capacitance vs. temperature)

2. C19 (470µF electrolytic): Place within 10mm of pin 1

• Purpose: Stabilize input voltage during load transients

• Polarity: Positive terminal to input, negative to ground

3. C15 (100nF ceramic): Place within 5mm of output tab

• Purpose: High-frequency output decoupling

• Critical for preventing oscillation

• Must be ceramic for low ESR/ESL

4. C20 (470µF electrolytic): Place within 10mm of output tab

• Purpose: Improve load transient response

• ESR: <2Ω for best performance

• Helps with sudden current demands

Ground Plane Connection

The TO-263-2 package requires careful PCB layout:

• Pin 2 (GND): Connect directly to ground plane with wide trace

• Tab (OUTPUT): Large copper pour for both electrical and thermal connection

• Thermal vias: Essential for heat dissipation to inner/bottom layers

• Keep-out area: Maintain clearance around pins for solder inspection

Performance Characteristics

Regulation Performance

Noise Performance

Protection Features

Built-in Protections

1. Thermal Shutdown: Automatically shuts down if junction temperature exceeds 150°C

2. Short Circuit Protection: Current limiting prevents damage during output short

3. Safe Operating Area (SOA): Internal circuitry ensures operation within safe limits

4. Reverse Polarity: Input diode protects against reverse voltage

External Protection (This Design)

+5V (from U7) ───┬─── PTC2: 1.1A ───┬─── F2: 1.5A ──┬─── TVS2: SD05 ────────┬─→ +5V OUT
                 │  (Auto-Reset)    │   (Backup)    │   (5V Clamp)          │
                 │                  │               │      ↕                │
                 │                  │               └─────GND────────────────┤
                 │                  │                                       │
                 └─── LED3 (Blue) via R8 (1kΩ) ──────────────→ Power Status

Protection stages:

1. Overload (0.6A-1.5A): PTC2 trips → Auto-reset after cooling

2. Short circuit (>1.5A): F2 blows → Manual replacement required

3. Overvoltage: TVS2 clamps transients above 6V (unidirectional)

Note: The TVS2 (SD05) is unidirectional, optimized for positive DC power rail protection.

Bill of Materials

Alternative Parts

Direct Replacements (TO-263-2 Package)

Package Alternatives

Recommendation: Stick with TO-263-2 for SMD assembly and superior thermal performance.

PCB Layout Guidelines

Footprint Requirements

TO-263-2 (D2PAK) package footprint specifications:

         Top View (PCB Pad Layout)

    ┌──────────────────────────────┐
    │                              │
    │    Large Copper Pour         │  ← OUTPUT TAB
    │    (5cm² recommended)        │     thermal + electrical
    │                              │
    │         Thermal Vias         │
    │         (6-10 vias)          │
    │                              │
    └──────────────────────────────┘

         PIN1 ■        PIN2 ■
        (INPUT)        (GND)

    Pin spacing: 2.54mm (0.1")
    Pin pad: 1.5mm x 2.0mm
    Tab pad: 10mm x 10mm (minimum)
            15mm x 15mm (recommended)

Recommended Pad Dimensions

Layout Recommendations

1. Component placement:

• Orient IC with tab facing interior of PCB (away from edge)

• Maximize copper area under and around tab

• Keep input and output capacitors on same side as regulator

2. Copper pours:

• Create large copper pour (5cm² minimum) connected to output tab

• Top layer: Main output pad and distribution

• Bottom layer: Additional copper connected via thermal vias

• Inner layers (4-layer board): Additional ground/power planes

3. Thermal vias:

• Place 6-10 thermal vias (0.3mm diameter) under tab

• Arrange in grid pattern for even heat distribution

• Connect to bottom layer copper pour

• Do NOT use thermal relief on these vias (direct connection needed)

• Via spacing: ~2mm apart

4. Trace widths:

• Input trace (7.5V): 0.5mm minimum (0.5A current, low voltage drop)

• Output trace (5V): 1mm minimum (0.5A current)

• Ground: Maximum copper pour area

• High-current paths: 2mm or copper pour preferred

5. Capacitor placement:

   C12 ──┐  ┌── IC ──┐  ┌── C15
         │  │        │  │
   C19 ──┘  │  U7    │  └── C20
            │        │
            └────────┘
   
   Distance:
   - C12: <5mm from pin 1
   - C19: <10mm from pin 1
   - C15: <5mm from output tab
   - C20: <10mm from output tab

Thermal Via Pattern

    Recommended thermal via pattern
    under TO-263-2 tab:

    ┌─────────────────────────┐
    │  ●    ●    ●    ●    ●  │
    │                         │
    │  ●    ●    ●    ●    ●  │  ← 0.3mm vias
    │                         │     2mm spacing
    │  ●    ●    ●    ●    ●  │
    │                         │
    └─────────────────────────┘

    Total vias: 15 (aggressive cooling)
    Minimum: 6 vias
    Recommended: 10 vias

Assembly Considerations

Soldering Guidelines

Reflow soldering (recommended for production):

• Peak temperature: 260°C maximum

• Time above 220°C: 60-90 seconds

• Solder paste: SAC305 or similar lead-free

• Stencil thickness: 0.125mm (5 mil)

Hand soldering:

• Soldering iron: 350°C maximum

• Solder pin 1 and pin 2 first

• Apply solder to tab from component side

• Ensure good thermal contact between tab and PCB pad

• Use generous solder for tab connection

Inspection Points

After assembly, inspect:

1. Pin solder joints: Smooth fillet, no bridges

2. Tab solder joint: Good coverage, no voids visible

3. Component alignment: Centered on pads

4. No cold solder joints: Shiny, smooth finish

5. Thermal via filling: Solder should wick into vias

Testing and Validation

Input Voltage Test

1. Apply 7.5V to input with no load

2. Verify output voltage: 4.8V - 5.2V (5V ±4%)

3. Measure quiescent current: <10mA

Load Regulation Test

1. Connect variable load (0-1.0A)

2. Measure output voltage at different load currents:

• 0mA: Should be within 5V ±2%

• 250mA: Should be within 5V ±3%

• 500mA: Should be within 5V ±4%

3. Verify voltage drop <50mV from no-load to full-load

Thermal Test

1. Apply 0.5A load for 30 minutes

2. Measure case temperature with thermal camera or thermocouple

3. Verify case temperature <70°C at 25°C ambient

4. Compare to calculation: Should be ~69°C

5. Check for thermal shutdown (should not occur)

Ripple and Noise Test

1. Connect oscilloscope (AC coupling, 20MHz bandwidth limit)

2. Use short ground lead or coax probe

3. Measure output with 0.5A load

4. Verify peak-to-peak ripple <5mVp-p (target: <1mVp-p)

5. Check for oscillation or instability (should be stable)

Transient Response Test

1. Use electronic load with step function (0A → 0.5A)

2. Monitor output voltage on oscilloscope

3. Verify voltage dip <250mV during load step

4. Verify recovery time <100µs

5. Check for ringing or overshoot

Troubleshooting

Application Notes

Digital vs. Analog Loads

The +5V rail in modular synthesizers may power:

Digital circuits (microcontrollers, logic ICs):

• Characteristics: Switching loads, transient currents

• Decoupling: Add 100nF ceramic capacitor at each IC

• Distribution: Star topology from main filter cap

Analog circuits (op-amps, comparators):

• Characteristics: Steady loads, noise-sensitive

• Decoupling: 100nF ceramic + 10µF electrolytic per section

• Isolation: Consider RC filter if needed (10Ω + 100µF)

Low-Noise Operation

For ultra-low-noise applications:

1. Additional output filtering:

• Add 10Ω resistor + 100µF capacitor LC filter

• Creates additional pole at ~160Hz

• Reduces high-frequency noise

2. Separate analog/digital grounds:

• Split +5V distribution into analog and digital sections

• Join grounds at single star point

• Prevents digital switching noise coupling

3. Shielding:

• Route +5V traces away from high-frequency signals

• Use ground plane as shield

• Keep sensitive analog circuits away from digital sections

Related Components

• Upstream: LM2596S-ADJ #2 (U3) - Provides +7.5V input

• Downstream: Protection circuit (PTC2, F2, TVS2)

• Parallel regulators: L7812CV-DG (U6), CJ7912 (U8)

References

• L7805ABD2T-TR Datasheet - STMicroelectronics

• JLCPCB Part C86206

• TO-263 Package Thermal Design

• Related documentation: Diagram6 - +5V Linear Regulator