Input Protection for most of the board¶
Device Overview¶
- Part Number: TPS4800-Q1
- Package: DGX (VSSOP, 19-pin)
- Function: 100V Automotive Low IQ High Side Driver with Protection
- Operating Voltage Range: 6-60V (application specific)
- Typical Application Voltage: 12V automotive systems
- Key Features: Reverse polarity protection to -65V, integrated charge pump, comprehensive fault detection
Pin-by-Pin Configuration¶
EN/UVLO (Pin 1) - Enable/Undervoltage Lockout¶
- Threshold: 1.24V rising, 1.14V falling (±4% tolerance)
- Voltage Divider: R1=470kΩ, R2+R3=105kΩ (total 575kΩ)
- Turn-On Voltage: 6.8V battery minimum
- Turn-Off Voltage: 6.25V battery minimum
- At 12V Battery: EN/UVLO pin = 2.19V (well above 1.24V threshold)
- Current Draw: 12V / 575kΩ = 20.9µA
- Rationale: Provides undervoltage lockout protection, keeps device off during deep battery discharge
OV (Pin 2) - Overvoltage Protection¶
- Threshold: 1.225V rising ±2% (1.20V to 1.25V)
- Design Requirement: 58.8V overvoltage protection (48V lithium system)
- Voltage Divider: R_top=487kΩ, R_bottom=10.2kΩ (total 497.2kΩ)
- OVP Trigger Range: 58.8V to 61.5V (accounting for threshold tolerance)
- At 12V Battery: OV pin = 0.246V (well below 1.225V threshold)
- Current Draw: 12V / 497.2kΩ = 24.1µA
- At 60V Battery: Current = 120.7µA
- Component Values: Both 487kΩ and 10.2kΩ are standard 1% resistors
INP (Pin 3) - Input Control Signal [Modified for USB-C Power Option]¶
- Thresholds: 2V high, 0.8V low
- Configuration: Jumper-controlled connection to VIN (6-60V)
- Implementation: 2-pin jumper header between VIN and INP pin
- Battery Mode (Jumper Installed): INP = VIN, device enabled when battery voltage present
- USB Mode (Jumper Removed): INP floating → internal 100nA pull-down → device disabled
- At 12V Battery: INP = 12V (well above 2V HIGH threshold)
- Behavior: Manual control - MOSFET enabled only when jumper installed
- Absolute Maximum: 70V (our 60V max is within limits)
- Power Isolation: Complete battery power path disconnect when jumper removed
ISCP (Pin 8) - Short Circuit Protection Threshold¶
- Design Requirement: 15A overcurrent protection
- Sense Resistor: 2mΩ (HoLLR2010-1.5W-2mR-1%, 2W, AEC-Q200)
- Calculation: RISCP = (15A × 0.002Ω - 19mV) / 2µA = 5.5kΩ
- Selected Value: 5.6kΩ (1%, standard value)
- Actual Protection Level: 15.1A
- Voltage Across Sense Resistor at Trip: 30.2mV
- At 12V Normal Operation: No effect on ISCP pin (current dependent)
- Note: EVM demo board values appear inconsistent with datasheet formula
TMR (Pin 9) - Fault Timer¶
- Design Requirement: ~5 second auto-retry interval
- Selected Value: 220nF ceramic capacitor to GND
- Short-Circuit Response Time: tSC = (220nF × 1.1V) / 80µA = 3.0µs
- Auto-Retry Interval: tRETRY = 22.7 × 10⁶ × 220nF = 5.0 seconds
- Behavior:
- Fault detected → 3µs delay → FET turns OFF
- Auto-retry after 32 charge/discharge cycles (5 seconds)
- Continues retrying until fault clears
- At 12V Battery: Timer behavior independent of supply voltage
Power Source Integration¶
USB-C Power Mode (INP Jumper Removed)¶
- USB Power Selection: J17 jumper on USB-C board enables 5V from VBUS
- Battery Isolation: Remove INP jumper → TPS4800-Q1 disabled → complete battery power path isolation
- Power Flow: USB 5V → existing 3.3V buck (TLV62569DBV) → ESP32-S3 + peripherals
- Battery Current: ~45µA (only voltage divider leakage, TPS4800 disabled)
- USB Current: ~400mA @ 5V for full system operation
- 5V Buck Safety: Safe to apply USB 5V to LMR36510ADDA output when TPS4800 input isolated
Battery Power Mode (INP Jumper Installed)¶
- Battery Power Selection: Remove J17 jumper (isolate USB power from 5V rail)
- Battery Enable: Install INP jumper → TPS4800-Q1 enabled
- Power Flow: Battery → TPS4800-Q1 → LMR36510ADDA (5V buck) → TLV62569DBV (3.3V buck) → ESP32-S3
- Battery Current: 88µA quiescent + load current
- USB Current: 0mA (USB power isolated)
Jumper Control Summary¶
| Jumper | Location | Function | Installed | Removed |
|---|---|---|---|---|
| INP Jumper | TPS4800-Q1 board | Battery enable | Battery power ON | Battery power OFF |
| J17 Jumper | USB-C board | USB power | USB power ON | USB power OFF |
Power Source Selection Matrix: | INP Jumper | J17 Jumper | Result | Battery Current | USB Current | |------------|------------|---------|-----------------|-------------| | Installed | Removed | Battery only | 88µA + load | 0mA | | Removed | Installed | USB only | 45µA | ~400mA | | Removed | Removed | No power | 45µA | 0mA | | Installed | Installed | ⚠️ CONFLICT | AVOID | AVOID |
Input Protection Design¶
Transient Protection Strategy¶
The design implements a hierarchical protection approach to handle automotive transients while preserving proper overvoltage protection functionality:
- Primary Protection: TPS4800-Q1 OV pin triggers controlled shutdown at 58.8V-61.5V
- Secondary Protection: External TVS diodes clamp severe transients above 64V
- Energy Storage: Input capacitors absorb transient energy during brief spikes
TVS Diode Configuration (on TPS4800-Q1 input)¶
Bidirectional TVS Clamp Bridge (Cathodes Tied Together):
D1 (Positive Rail Protection): - SMBJ64A (64V unidirectional TVS) - Connection: Anode to GND, Cathode to shared node - Breakdown Range: 60.8V-67.2V - Soft Conduction: Begins ~65V (above OV protection range) - Function: Clamps positive transients >64V to ~76-103V range
D7 (Negative Rail Protection): - SMBJ75A (75V unidirectional TVS) - Connection: Anode to VIN, Cathode to shared node - Breakdown Range: 71.3V-83.3V - Redundant Protection: Backs up TPS4800-Q1's internal -65V protection - Function: Clamps negative transients <-75V to ~-90 to -121V range
Shared Cathode Node: Creates floating reference point for bidirectional clamping
Topology Benefits:
- Positive overvoltage: D1 avalanche breakdown clamps high VIN
- Negative overvoltage: D7 avalanche breakdown clamps low VIN
- Reverse polarity: Both diodes forward conduct (~1.4V drop), creating controlled short to trip upstream protection
- No interference: TVS breakdown voltages above TPS4800-Q1 OVP threshold
Protection Hierarchy Operation¶
- 6V-58V Normal: No protection active, normal operation
- 58.8V-61.5V: OV protection triggers, controlled MOSFET shutdown
- 64V+: TVS conducts, absorbs transient energy, prevents chip damage
- Negative spikes: TVS and internal protection both active
Component Summary¶
| Component | Value | Tolerance | Type | Function |
|---|---|---|---|---|
| R1 (EN/UVLO top) | 470kΩ | 1% | Resistor | UVLO voltage divider |
| R2+R3 (EN/UVLO bottom) | 105kΩ | 1% | Resistor | UVLO voltage divider |
| R_OV_top | 487kΩ | 1% | Resistor | OVP voltage divider |
| R_OV_bottom | 10.2kΩ | 1% | Resistor | OVP voltage divider |
| RISCP | 5.6kΩ | 1% | Resistor | Short-circuit threshold |
| CTMR | 220nF | - | Ceramic Cap | Fault timer |
| CBST | 100nF | - | Ceramic Cap | Bootstrap capacitor |
| RSNS | 2mΩ | 1% | Power Resistor | Current sensing (2W, AEC-Q200) |
| D_POS (TVS) | SMBJ64A | - | TVS Diode | Positive transient protection |
| D_NEG (TVS) | SMBJ75A | - | TVS Diode | Negative transient protection |
| C_INPUT | 11µF total | - | Capacitors | Input energy storage |
| INP Jumper | 2-pin header | - | Jumper | Battery power isolation control |
Performance Analysis¶
Battery Mode Operation (INP Jumper Installed)¶
| Parameter | Value | Notes |
|---|---|---|
| EN/UVLO Current | 20.9µA | Through voltage divider |
| OV Current | 24.1µA | Through voltage divider |
| Total Divider Current | 45.0µA | At 12V battery |
| Device Quiescent Current | 43µA typical | From datasheet |
| Total System Current | ~88µA | Excluding load current |
| Short-Circuit Protection | 15.1A | Fast 3µs response |
| Auto-Retry Interval | 5.0 seconds | If fault persists |
USB Power Mode (INP Jumper Removed)¶
| Parameter | Value | Notes |
|---|---|---|
| EN/UVLO Current | 20.9µA | Still through voltage divider |
| OV Current | 24.1µA | Still through voltage divider |
| Device Quiescent Current | 0µA | Device disabled (INP floating) |
| Total Battery Current | 45.0µA | Only voltage divider leakage |
| TPS4800 Output | High impedance | MOSFETs disabled |
| Battery Power Path | Isolated | No power delivery to 5V buck |
| Current Savings | 43µA | TPS4800 quiescent eliminated |
Protection Summary¶
| Protection Type | Threshold | Response | Active When |
|---|---|---|---|
| Undervoltage Lockout | 6.8V battery | Device shutdown | INP jumper installed |
| Overvoltage Protection | 58.8V - 61.5V battery | FET shutdown, FLT asserted | INP jumper installed |
| Overcurrent Protection | 15.1A load current | 3µs response, auto-retry | INP jumper installed |
| Reverse Polarity | -65V maximum | Built-in protection | INP jumper installed |
| USB Power Isolation | Manual | Complete battery disconnect | INP jumper removed |
Power Consumption Analysis¶
Battery Mode (INP Jumper Installed)¶
| Supply Voltage | EN/UVLO Current | OV Current | TPS4800 Quiescent | Total Current | Total Power | Equivalent @ 12V |
|---|---|---|---|---|---|---|
| 13V | 22.6µA | 26.1µA | 43µA | 91.7µA | 1.19mW | 0.099mA |
| 26V | 45.2µA | 52.3µA | 43µA | 140.5µA | 3.65mW | 0.304mA |
| 52V | 90.4µA | 104.6µA | 43µA | 238µA | 12.38mW | 1.032mA |
USB Mode (INP Jumper Removed)¶
| Supply Voltage | EN/UVLO Current | OV Current | TPS4800 Quiescent | Total Current | Total Power | Equivalent @ 12V |
|---|---|---|---|---|---|---|
| 13V | 22.6µA | 26.1µA | 0µA | 48.7µA | 0.63mW | 0.053mA |
| 26V | 45.2µA | 52.3µA | 0µA | 97.5µA | 2.54mW | 0.212mA |
| 52V | 90.4µA | 104.6µA | 0µA | 195µA | 10.14mW | 0.845mA |
Notes: - EN/UVLO divider: 575kΩ total (470kΩ + 105kΩ) - always active for monitoring - OV divider: 497.2kΩ total (487kΩ + 10.2kΩ) - always active for monitoring - TPS4800-Q1 quiescent current: 43µA typical when enabled, 0µA when INP disabled - Power excludes load current through MOSFETs - "Equivalent @ 12V" shows power consumption as current draw on a 12V system - USB mode power savings: 43µA reduction from TPS4800 shutdown
Further Optimization Potential¶
- Voltage divider jumpers: Could add jumpers to EN/UVLO and OV dividers for complete battery isolation (~0µA)
- Current implementation: Maintains monitoring capability even in USB mode
- Trade-off: 45µA monitoring current vs complete battery isolation
Design Notes¶
- INP control: Cleanest method for battery power path isolation without affecting protection monitoring
- All resistor values: Standard 1% E96 series for easy sourcing
- Low current draw: Design suitable for always-on automotive applications
- Fast overcurrent protection: 3µs response with reasonable 5-second retry intervals
- Conservative margins: All protection thresholds have adequate safety margins
- Production ready: Manual jumper control suitable for field service and development
- Power source safety: No possibility of conflicts with proper jumper management
- LMR36510ADDA compatibility: Safe to apply USB 5V to buck output when TPS4800 input isolated
- EVM discrepancy: Demo board documentation appears to contain calculation errors vs datasheet
- Reverse polarity behavior: Still not fully understood without back-to-back output MOSFETs. Will populate both TVS but DNP for initial testing. TI datasheet inadequate for this specific configuration.