30V/1.2A High‑dimming‑ratio Buck LED Constant‑Current Driver PT4115｜PT4115B89E / PT4115BSOH｜CRMICRO Authorized Level‑1 Distributor｜GSMicro

Keywords: PT4115B89E | PT4115BSOH | PT4115B89E‑B | PT4115BSOH‑B | 30V LED constant‑current driver | PWM dimming driver IC | CRMICRO

Product Overview: PT4115 Series (PT4115B89E/PT4115B89E‑B/PT4115BSOH/PT4115BSOH‑B) is CRMICRO buck LED constant‑current driver adopting continuous inductor conduction mode. 8‑30V input, max 1.2A output, supports analog / PWM high‑ratio dimming. Available in SOT89‑5 / ESOP8 packages for automotive lighting, commercial LED spotlights and industrial display applications. GSMicro is CRMICRO authorized level‑1 distributor with stock available. Samples, datasheets and hardware reference designs are provided.

⚡ Key Features

• Few external components required

• Wide input‑voltage range: 8V ~ 30V

• Maximum output current: 1.2A

• Multiplexed DIM pin: LED ON/OFF control, analog dimming, PWM high‑ratio dimming

• Output current accuracy ±5%

• Built‑in LED open‑circuit protection

• Conversion efficiency up to 97%

• Externally configurable constant‑current output

• ESOP8 package with enhanced thermal performance for high‑power LED driving

Typical Application Scenarios

• Low‑voltage LED spotlights (halogen lamp replacement)

• Automotive LED lamps

• LED backup lighting fixtures

• LED signal lights

PT4115 Full‑series Model Description

• PT4115B89E: SOT89‑5 package, standard industrial grade

• PT4115B89E‑B: SOT89‑5 package, enhanced / customized version

• PT4115BSOH: ESOP8 package with enhanced thermal dissipation for high‑power driving

• PT4115BSOH‑B: ESOP8 package, enhanced / customized version

Package‑Temperature‑Thermal Performance Table:

• PT4115B89E / PT4115B89E‑B｜SOT89‑5｜‑40℃~+85℃｜Standard thermal performance, suitable for compact PCB layout

• PT4115BSOH / PT4115BSOH‑B｜ESOP8｜‑40℃~+85℃｜Enhanced heat dissipation, supports higher‑power output

Typical Application Schematic

Pin Definition

Operating Principle

PT4115B89E / PT4115BSOH, together with inductor (L) and current‑sense resistor (RS), forms a self‑oscillating buck constant‑current LED controller with continuous inductor‑current mode. When VIN powers up, the initial current of inductor L and sense resistor RS equals zero, so LED output current is zero. The CS comparator outputs high level to turn on internal power switch, pulling SW pin low. Current flows through inductor L, sense resistor RS, LED string and internal power switch to GND.

Current rising slope is determined by VIN, inductor L and LED forward voltage drop. A differential voltage V_CSN is generated across RS. When (V_IN‑V_CSN)＞115mV, CS comparator outputs low to turn‑off internal power MOSFET. Inductor freewheeling current flows through L, RS, LED and Schottky diode D. When (V_IN‑V_CSN)＜85mV, power switch turns‑on again. This cycle repeats to stabilize average LED output current.

High‑side current‑sensing architecture reduces BOM components. With 1% precision sense resistor, LED output‑current accuracy reaches ±5%.

The DIM pin supports PWM dimming: output shuts off below 0.3V and fully enables above 2.5V. Supported PWM frequency ranges from 100Hz up to 20kHz+. Analog dimming can be implemented with DC voltage between 0.5V‑2.5V. DIM pin can be left floating. Pull DIM below 0.3V to enter standby mode with typical quiescent current of 95uA.

The IC integrates TSD thermal shutdown protection with 160℃ trigger threshold. ESOP8 package provides exposed thermal pad to improve reliability under high‑current operation. An external NTC thermistor can be connected to DIM pin to sense LED temperature and dynamically limit output current for LED thermal protection.

Application Notes

Setting Average LED Current via External Sense Resistor RS

Average LED output current is defined by sense resistor RS placed between VIN and CSN: I_OUT＝0.1/Rs (Rs≥0.082Ω). This formula is valid when DIM pin is floating or DIM voltage＞2.5V and less than 5V. RS sets maximum output current, while DIM pin can reduce actual output current.

Analog Dimming (DC‑voltage Dimming)

Applying DC V_DIM to DIM pin can decrease LED output current; maximum current is determined by RS.

Full‑scale output current I_OUT=0.1/Rs is maintained when V_DIM ranges from 2.5V to 5V.

PWM Signal Dimming

Maximum output current is set by RS. Brightness adjustment is achieved by feeding PWM signals with variable duty cycle to DIM pin. PWM dimming advantage: LED chromaticity will not shift. Recommended PWM frequency ≥100Hz to avoid visible flicker; maximum frequency can exceed 20kHz.

Shutdown Mode

Applying voltage below 0.3V to DIM pin activates shutdown mode, typical quiescent current is 95μA.

Soft‑Start Mode

Place an external capacitor from DIM pin to GND for slow voltage ramp‑up to realize LED‑current soft‑start. Approximate relation: 0.8ms/nF.

LED Open‑Circuit Protection

When LED load opens, SW pin floats and IC enters low‑power safe mode. Normal operation automatically resumes after load is reconnected.

Bypass Capacitor Selection

Place low‑ESR bypass capacitor close to VIN pin. Minimum value 4.7μF for DC input; 100μF tantalum capacitor is recommended for AC‑rectified input. X5R / X7R dielectric capacitors are preferred for stability over temperature and voltage range.

Inductor Selection

Recommended inductor value: 27uH ~ 100uH. Inductor saturation current must exceed actual output current by 30%‑50%. Larger inductance is preferred for lower output current. Mount inductor close to VIN and SW pins on PCB layout.

SW On‑Time / Off‑Time calculation formulas:

Diode Selection

Select fast‑recovery Schottky diode with low forward drop and low leakage current. Derate current and voltage ratings by more than 30%. Pay attention to reverse leakage under high‑temperature conditions.

Reducing Output Ripple

Parallel a capacitor across LED terminals to suppress output ripple; 1uF capacitor can reduce ripple by approx. 1/3. Output capacitor affects startup delay and dimming response speed.

Low‑voltage Input, Thermal Design, Thermal Compensation & PCB Layout Guidelines

• When input voltage is close to total LED forward voltage, duty ratio rises and power dissipation increases. Maintain sufficient voltage headroom to avoid frequent thermal‑shutdown events.

• The exposed thermal pad of ESOP8 package must be connected to large‑area PCB GND copper pour for better heat dissipation; ESOP8 is preferred for high‑power applications.

• NTC thermistor connected to DIM pin enables LED‑temperature‑based thermal compensation for output‑current adjustment.

• TSD thermal‑shutdown: IC junction temperature reaches 160℃ triggers shutdown; auto‑recovery occurs when temperature drops below 140℃.

• PCB layout: Keep SW trace as short as possible; place inductor and sense resistor RS close to IC pins; maximize copper area for thermal pad; locate bypass capacitor near power‑supply pin.

Q1: How to set maximum output current for PT4115B89E?
A: Constant‑current output is configured by sense resistor RS between VIN‑CSN. Formula Iout=0.1/Rs, minimum RS value 0.082Ω.

Q2: What dimming modes are supported by DIM pin?
A: DIM pin supports PWM digital dimming and 0.5V‑2.5V analog‑voltage dimming. DIM＜0.3V shuts down IC output and enters standby state.

Q3: What are the differences between SOT89‑5 and ESOP8 versions?
A: PT4115B89E uses SOT89‑5 standard package. PT4115BSOH uses ESOP8 package with exposed thermal pad for superior heat dissipation, suitable for high‑power LED‑driving applications.

Q4: How to handle thermal‑shutdown events of PT4115 series?
A: Check voltage headroom between input and output; optimize PCB thermal design, ensure ESOP8 exposed pad connects to large‑area GND copper pour; verify inductor and Schottky‑diode power ratings match application requirements.

Q5: Will IC get damaged if LED load is open‑circuited?
A: Built‑in LED open‑circuit protection. IC enters low‑power safe mode upon open‑circuit fault and resumes normal operation after load reconnection.