The U3115 is a single-phase high- and low-side gate driver IC designed for half-bridge topologies, supporting a floating supply voltage up to 250V. It is ideal for medium-to-high power applications such as motor drives, inverters, and home appliances (e.g., air conditioners, washing machines). Featuring a bootstrap architecture, built-in shoot-through protection, under-voltage lockout (UVLO), high dV/dt immunity (±50 V/ns), and strong drive capability (1.2A source / 1.5A sink), the U3115 significantly simplifies half-bridge driver design.
1. Key Features Overview
Based on the U3115 datasheet:
Operating Voltage: High-side floating channel up to 250V (at VS pin)
Drive Strength: 1.2A source / 1.5A sink (pulse ≤10 μs)
Logic Input Compatibility: Supports 3.3V, 5V, and 15V CMOS/LSTTL levels
Dead Time: Built-in 200 ns shoot-through prevention dead time
Propagation Delay: Typical 150 ns (on) / 140 ns (off), with ≤50 ns matching
Noise Immunity:
dV/dt Immunity: ±50 V/ns
Negative VS Tolerance: –9 V (50 ns pulse)
Under-Voltage Lockout (UVLO):
Turn-on threshold: 5.5 V
Turn-off threshold: 5.0 V
Hysteresis prevents chatter during supply fluctuations
Operating Temperature: –40°C to +125°C
Packages: SOIC8 / DFN8 (2mm × 3mm)
2. Pin Functions (8-Pin)
| Pin | Name | Description |
|---|---|---|
| 1 | VCC | Supply for low-side and logic circuitry (6–20V) |
| 2 | HIN | High-side PWM input (3.3V+ compatible) |
| 3 | LIN | Low-side PWM input |
| 4 | VSS | Ground reference (low-side return) |
| 5 | LO | Low-side gate drive output (push-pull) |
| 6 | VS | High-side floating ground (connect to high-side MOSFET source) |
| 7 | HO | High-side gate drive output (push-pull) |
| 8 | VB | High-side floating supply (typically from bootstrap circuit) |
3. Critical Design Guidelines
(1) Bootstrap Circuit (Mandatory)
The high-side driver requires a bootstrap circuit consisting of a bootstrap diode (Dboot) and capacitor (Cboot).
Recommended values:
Cboot: 0.1–1 μF low-ESR ceramic capacitor (add electrolytic in parallel for long on-time)
Dboot: Fast-recovery or Schottky diode, reverse voltage rating > VCC (e.g., 100V)
⚠️ 100% duty cycle on the high-side is not allowed, as Cboot needs off-time to recharge.
(2) Dead Time & Shoot-Through Protection
Internal 200 ns dead time ensures safe switching.
If both HIN and LIN are high simultaneously, both HO and LO are forced low to prevent shoot-through.
Internal pull-down/pull-up resistors (800kΩ) allow floating inputs, but it’s recommended to tie HIN to VSS and LIN to VCC when unused.
(3) Gate Resistor Selection
Add a gate resistor (Rg = 20–120 Ω) between HO/LO and MOSFET gate.
Benefits:
Suppresses gate ringing (prevents MOSFET damage)
Controls dv/dt to reduce EMI
Balances switching loss vs. reliability
(4) Power Supply Decoupling
Place a ≥1 μF low-ESR ceramic capacitor between VCC and VSS, close to the IC.
Similarly, ensure low-ESR capacitance between VB and VS (i.e., Cboot).
(5) PCB Layout Best Practices
Minimize gate drive loop area: Keep traces from HO→Gate→Source→VS and LO→Gate→Source→VSS short and wide.
Isolate VS node: VS experiences high dV/dt; avoid routing near sensitive logic signals.
Thermal pad (DFN8): Solder the exposed pad to a large copper pour tied to VSS for optimal heat dissipation.
(6) Negative VS Tolerance
The VS pin can withstand –9V for 50 ns, accommodating inductive kickback without external clamping.
4. Typical Applications
Single-phase half/full-bridge motor drives (BLDC, PMSM)
Micro solar inverters
Inverter-driven compressors in ACs / washing machines
General-purpose DC-AC inverters
5. Summary
The U3115 delivers a robust, integrated solution for half-bridge applications with its high voltage rating, strong drive capability, built-in dead time, UVLO, and excellent noise immunity. By carefully designing the bootstrap circuit, selecting appropriate gate resistors, and following good PCB layout practices, engineers can achieve a compact, efficient, and highly reliable power stage for demanding industrial and consumer applications.
