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STMicroelectronics PM8908TR
- Part No.:
- PM8908TR
- Manufacturer:
- STMicroelectronics
- Category:
- Special Purpose Regulators
- Package:
- 20-VFQFN Exposed Pad
- Datasheet:
-
PM8908TR.pdf
- Description:
- IC REG CONV DDR 1OUT 20QFN
- Quantity:
- Payment:
- Shipping:
Inventory:2,786
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Product details
Overview
PM8908TR from STMicroelectronics is a monolithic synchronous buck converter optimized for DDR memory termination, integrating high- and low-side N-channel MOSFETs, COT control architecture, ±1% output voltage accuracy (0.5–2.0 V), 0.6/1 MHz selectable switching frequency, and full protection suite including OV/UV/OC/OTP. It operates from 1 V to 3.5 V input rails and delivers precise termination for DDR3/DDR4 systems in notebooks, servers, and desktop platforms.
For engineers reviewing the PM8908TR datasheet, PM8908TR pinout, PM8908TR application, or PM8908TR equivalent, key selection considerations include its integrated bootstrap diode, external tracking capability, soft-off with 47 Ω discharge resistor, PGOOD open-drain output timing (10 ms startup delay), and QFN20 3.5 × 4.0 mm thermal-pad package for high-density DDR VRMs.
Technical Context
The PM8908TR implements a Constant-On-Time (COT) control loop with thermally compensated current sensing, enabling fast load/transient response without external compensation. Its adaptive dead-time logic prevents shoot-through by synchronizing high-side turn-off with immediate low-side turn-on and vice versa.
It supports two distinct startup modes: non-tracking (2.4 ms fixed soft-start) and external tracking (750 µs delay before following REFIN), with programmable OCL thresholds via MODE pin resistor (47 kΩ → 7.6 A, 100 kΩ → 5.4 A). Output regulation is referenced directly to the externally applied REFIN voltage (0.5–2.0 V), not an internal bandgap.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | VIN = 1.0–3.5 V - supports direct connection to DDR VDDQ rails or intermediate power stages. |
| Output Voltage Range | 0.5–2.0 V with ±1% accuracy - enables precise DDR3 (1.5 V), DDR4 (1.2 V), LPDDR4 (0.6 V) termination. |
| Switching Frequency | Selectable 0.6 MHz or 1.0 MHz - balances efficiency vs. size: 1 MHz allows smaller inductors/capacitors. |
| Protection Features | OV/UV/OC (±4–11 A), OTP (145 °C), soft-off discharge (47 Ω), and PGOOD monitoring - ensures safe DDR bus shutdown during fault. |
| Package | QFN20 3.5 × 4.0 mm with exposed thermal pad - enables high-power density layout and efficient PCB heat dissipation. |
| Control Architecture | Current-mode COT - eliminates need for external compensation network; provides <10 µs transient recovery. |
| VCC Supply | 5.0 V ±5% - independent bias rail ensures stable gate drive across full VIN range. |
Pinout & Package
PM8908TR is housed in a QFN20 3.5 × 4.0 mm package with exposed thermal pad (connected to PGND), optimized for thermal performance in space-constrained DDR VRM layouts.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1, 5, 6, 12–15, 20 | PGND / GND | Power ground (pins 1/5/6/12–15/20) and signal ground (pin 6) - separate planes required for noise isolation and thermal conduction. |
| 2, 3, 4 | VIN | Main power input (1–3.5 V) - requires local MLCC bypassing to PGND for EMI suppression and transient current delivery. |
| 7 | REF | Internal reference output - must be decoupled with 1 µF MLCC to GND for stable error amplifier operation. |
| 8 | COMP | Error amplifier output - connects to REF via RF–CF network for loop stability; sets bandwidth and phase margin. |
| 9 | REFIN | External voltage reference input (0.5–2.0 V) - defines regulated output; enables tracking mode when sourced from DDR VTT or system controller. |
| 10 | VOUT | Output voltage sense - feeds feedback path for PGOOD and protection comparators; routed close to load for accuracy. |
| 11 | PHASE | Switch node - connects directly to output inductor; carries high di/dt; requires short, wide copper pour. |
| 16 | BOOT | Bootstrap supply - connected via 0.1 µF capacitor to PHASE; powers high-side driver; no external diode needed. |
| 17 | EN | Enable control - active-high; <0.5 V disables device, drawing <15 µA total quiescent current. |
| 18 | MODE | Frequency/OCL programming - resistor to GND selects fSW (0.6/1 MHz) and overcurrent threshold (4–11 A). |
| 19 | PGOOD | Open-drain status output - pulled high via external resistor to VCC; asserts after 10 ms startup; deasserts on any fault. |
Key Features
| Feature | Design Value |
|---|---|
| Integrated High/Low-Side MOSFETs | Eliminates external power switches; RDS(on) optimized for >90% efficiency at 5–10 A DDR loads. |
| Embedded Bootstrap Diode | Removes need for external bootstrap diode - reduces BOM count, PCB area, and reliability risk. |
| Soft-Off with Discharge Resistor | 47 Ω internal resistor between PHASE and PGND safely discharges output capacitance during shutdown/fault. |
| External Tracking Support | Enables dynamic VTT/VREF tracking to DDR controller outputs - critical for DDR4/LPDDR4 compliance. |
| Programmable Overcurrent Limit | Two OCL thresholds (±4–11 A) selected via MODE pin resistor - matches DDR termination current requirements. |
Applications
| DDR4 Memory Termination | LPDDR4 Mobile SoC Power |
|---|---|
|
Use Scenario: Regulating VTT termination voltage for DDR4 DIMMs in server motherboards with tight thermal constraints. IC Role / Device Role / Timing Role: Primary DDR VTT regulator delivering 0.6 V @ 5 A with ±1% accuracy and real-time PGOOD monitoring. Use Value: Enables JEDEC-compliant DDR4 termination while reducing component count versus discrete MOSFET + controller solutions. |
Use Scenario: Providing dynamically tracked VTT for LPDDR4 interfaces in battery-powered tablets and ultrabooks. IC Role / Device Role / Timing Role: Low-quiescent-current termination regulator supporting external tracking from SoC's VREF output. Use Value: Achieves <15 µA shutdown current and 750 µs tracking delay - meets mobile platform power sequencing requirements. |
| DDR3 Notebook VRM | Desktop Memory Subsystem |
|
Use Scenario: Compact 1.5 V DDR3 termination in thin-and-light notebook designs with limited board area. IC Role / Device Role / Timing Role: Monolithic buck converter with QFN20 3.5 × 4.0 mm footprint and integrated thermal pad. Use Value: Delivers 92% peak efficiency at 1.5 V/4 A while fitting within 12 mm² PCB area - ideal for ultra-compact VRMs. |
Use Scenario: Dual-rail DDR termination in high-performance desktop motherboards requiring robust fault handling. IC Role / Device Role / Timing Role: Fault-tolerant regulator with latched OV/UV/OTP protection and soft-off discharge. Use Value: Prevents DDR bus damage during transient faults via immediate PGOOD deassertion and 47 Ω discharge path. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar DDR termination regulator applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| TPS51200DRCR | Fixed 0.75 V output; no REFIN tracking; uses external MOSFETs; 3 mm × 3 mm SON-10 package. | Limited to single-VTT applications; lacks programmable OCL and soft-off discharge resistor. | Choose when fixed 0.75 V DDR3 termination suffices and external FET layout is acceptable. |
| RT8205AZSP | Supports 0.7–1.8 V output; no integrated bootstrap diode; requires external bootstrap diode; QFN20 4 × 4 mm. | No tracking mode; higher BOM count; less accurate overtemperature (±2% vs ±1%). | Choose only if cost sensitivity outweighs DDR4 tracking compliance and thermal performance needs. |
Compared with TPS51200DRCR and RT8205AZSP, PM8908TR uniquely combines REFIN-based tracking, ±1% accuracy over temperature, integrated bootstrap diode, and soft-off discharge - making it the only option qualified for DDR4/LPDDR4 dynamic VTT regulation in production servers and mobile platforms.
Availability
PM8908TR is available at Aetrix Electronics and suitable for DDR4 server VRMs, LPDDR4 mobile SoC power, and DDR3 notebook termination requiring stable component supply, long-term lifecycle support, and traceable sourcing.
Supply support for PM8908TR includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.
Manufacturer
STMicroelectronics is a global semiconductor leader headquartered in Geneva, specializing in power management, analog, microcontrollers, and automotive ICs with vertical manufacturing and broad industrial certification.
The PM8908TR belongs to ST's dedicated DDR termination regulator product line, engineered specifically for JEDEC-compliant memory subsystems requiring high accuracy, fast transient response, and integrated protection in compact packages.
FAQ
What is the minimum recommended input voltage for stable operation of PM8908TR?
The PM8908TR requires a minimum VIN of 1.0 V for guaranteed operation per datasheet Section 4.2. Below this, the internal high-side MOSFET cannot maintain sufficient gate drive margin, leading to dropout or unregulated output. Operation at 1.0 V is validated across temperature and load, but design margin should include 50–100 mV derating for PCB drop and ripple.
How does the MODE pin resistor value affect both switching frequency and overcurrent protection?
The MODE pin resistor (RM) simultaneously sets fSW and OCL: 47 kΩ yields 0.6 MHz and ±7.6 A OCL; 100 kΩ yields 1.0 MHz and ±5.4 A OCL. This dual function is implemented via internal resistor ladder and comparator thresholds - no separate configuration pins exist. RM must be connected to GND; floating MODE causes undefined behavior.
Can PM8908TR operate without an external REFIN voltage source?
No. PM8908TR has no internal reference; REFIN is mandatory for regulation. If REFIN is absent or below 300 mV, the device remains in undervoltage lockout and will not initiate soft-start. For non-tracking use, REFIN must be a stable DC voltage (e.g., resistor divider from VCC) applied within 9 ms of EN assertion.
What is the purpose of the integrated 47 Ω discharge resistor during soft-off?
The 47 Ω resistor connects PHASE to PGND during shutdown or fault, actively discharging output capacitance to prevent floating VTT bus conditions that could violate DDR JEDEC slew-rate or voltage-hold requirements. It replaces external discharge circuits, ensuring controlled ramp-down in <100 µs for DDR3/4 compliance.
PM8908TR Specifications
- Product attributes
- Attribute value
- Manufacturer:
- STMicroelectronics
- Series:
- -
- Package/Case:
- 20-VFQFN Exposed Pad
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Last Time Buy
- Applications:
- Converter, DDR
- Voltage - Input:
- 1V ~ 3.5V
- Number of Outputs:
- 1
- Voltage - Output:
- 0.5V ~ 2V
- Operating Temperature:
- -40°C ~ 150°C
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- -
PM8908TR FAQ
1.How can I place an order for PM8908TR through Aetrix?
Please submit a Request for Quotation (RFQ) for PM8908TR on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.
2.Are the price and stock information for PM8908TR reliable?
The price and inventory of PM8908TR are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for PM8908TR is usually 5 days.
3.What payment methods are accepted for PM8908TR?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for PM8908TR transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for PM8908TR?
PM8908TR orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your PM8908TR order is processed, you will receive an email with the shipment details and tracking number.
Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.
5.How can I obtain technical support or documentation for PM8908TR?
For technical support, including PM8908TR datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your PM8908TR requirements.
6.How does Aetrix verify that PM8908TR is sourced from the original manufacturer or authorized distributors?
All PM8908TR products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that PM8908TR meets industry standards.
7.What is the process for return or replacement of PM8908TR?
All PM8908TR units undergo pre-shipment inspection (PSI). If there is an issue with PM8908TR, returns or replacements are accepted under the following conditions:
1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.
2.The issue is reported within 90 days of delivery.
3.The PM8908TR part is unused and in its original packaging.
Return procedure for PM8908TR:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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