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F29H850TU: Supply design

Patrick Ruf
Genius 5075 points

Part Number: F29H850TU
Other Parts Discussed in Thread: LP8758-E3, TPS3840

Hi,

Does TI has a recommendation for a supply design for the F29H850TU that is based on already available DC/DC converter?
I'm looking for a design for an industrial environment with 24V nominal input voltage (no functional safety requirements). Beside the needed voltages for the F29 (3.3V and 1.25V) with the mandatory sequence and slew rates we also need a +5V.
I had a look to the TPS650366 (TPS65036604RAYRQ1 or TPS65036605RAYRQ1) but it looks as this PMIC is not yet available or there are still some documentations missing (e.g. OTP parameter).

Thanks and best regards,
Patrick

  • 0
    TI__Mastermind 33873 points

    Hi Patrick,

    TI does not publish a specific reference design for powering the F29H850TU from a 24V industrial input. However, a workable architecture can be assembled from existing TI DC/DC converters. Here's what you need to know:

    F29H850TU Power Requirements

    From the datasheet 1:

    Parameter Min Max Unit
    VDDIO/VDDA (3.3V) slew rate 3 100 mV/µs
    VDD (1.25V) slew rate 2 100 mV/µs
    Total VDD decoupling 10 22 µF
    VDDIO decoupling per pin — 0.1 µF

    Sequencing requirement: VDDIO (3.3V) must ramp first, then VDD (1.25V) follows. The delay between the two ramps is specified with a minimum of 0 µs (i.e., VDD cannot lead VDDIO) 1.

    Recommended Architecture

    Since no single TI PMIC accepts 24V directly and provides all three rails with sequencing, a two-stage approach is practical:

    Stage 1: 24V → 5V (Wide-Input Buck)

    • LM5145 — Synchronous buck controller, 6–75V input, suitable for 24V industrial with wide transient tolerance. Generates your 5V system rail.
    • LM25145 — Similar wide-input buck controller, 6–42V input range.

    Either device handles the 24V input directly and produces a regulated 5V output.

    Stage 2: 5V → 3.3V + 1.25V (PMIC with Sequencing)

    From the 5V intermediate rail, use a multi-output PMIC with integrated sequencing:

    • TPS65220 — 3 buck converters + 4 LDOs, 2.5–5.5V input, integrated power sequencing. Can generate both 3.3V and 1.25V with proper startup order.
    • TPS65219 — 3 synchronous bucks with integrated sequencing, similar input range.
    • LP8758-E3 — 4 buck converters with adjustable slew rate control, which directly addresses the F29's slew rate requirements.

    The LP8758-E3 is particularly relevant given its explicit slew rate control feature.

    Additional Design Note

    The F29H850TU's internal VDD POR trips below the minimum recommended VDD (1.14V), so it cannot be relied upon for supply supervision. For robust operation, add an external voltage supervisor on the VDD rail 2. Since you have no functional safety requirements, a simple supervisor (e.g., TPS3840) monitoring VDD driving XRSn is sufficient.

    Follow up: What are your estimated current requirements on each rail (5V, 3.3V, 1.25V), and what is the expected input voltage range around the 24V nominal?

    1. F29H850TU Datasheet - Power Sequencing & Electrical Specs
    2. E2E: F29H850TU VDD POR Availability
    3. F29H850TU Migration Guide

    Best Regards,

    Zackary Fleenor