LTM4700 no-OS Driver

Supported Devices

Overview

The LTM4700 is a dual 50A or single 100A step-down µModule regulator featuring remote configurability and telemetry-monitoring of power management parameters over PMBus—an open standard I2C-based digital interface protocol.

The LTM4700 is comprised of fast analog control loops, precision mixed-signal circuitry, EEPROM, power MOSFETs, inductors and supporting components.

Key Features

  • Dual 50A or Single 100A Digitally Adjustable Outputs

  • Wide Input Voltage: 4.5V to 16V

  • Output Voltage Range: 0.5V to 1.8V

  • ±0.5% Maximum DC Output Error Over Temperature

  • ±3% Current Readback Accuracy (25°C to 125°C)

  • 400kHz PMBus-Compliant I2C Serial Interface

  • Integrated 16-Bit ∆Σ ADC for telemetry

  • Constant Frequency Current Mode Control

  • Internal EEPROM with Fault Logging and ECC

Supported Features

  • Device identification

  • Dual-channel voltage and current monitoring

  • LINEAR11/LINEAR16 data format conversion

  • Comprehensive status monitoring

  • PMBus command interface

  • NVM operations for configuration storage

  • Peak value tracking

  • IIO framework integration

Communication Interface

The device uses PMBus 1.3 compliant I2C interface:

  • Bus Speed: Up to 400kHz

  • Default Address: 0x5A (7-bit)

  • Data Formats: LINEAR11, LINEAR16

  • CRC Support: Optional polynomial 0x7

Device Variants

Device

Special ID

Description

LTM4700

0x4130

Dual 50A or Single 100A µModule

PMBus Commands

The driver supports standard PMBus commands and manufacturer-specific commands:

Standard Commands:

  • PAGE, OPERATION, CLEAR_FAULTS

  • VOUT_COMMAND, VOUT_MAX, VOUT_MARGIN_HIGH/LOW

  • STATUS_BYTE, STATUS_WORD, STATUS_VOUT, STATUS_IOUT

  • READ_VIN, READ_IIN, READ_VOUT, READ_IOUT

  • READ_TEMPERATURE_1/2, READ_POUT, READ_PIN

Manufacturer Commands:

  • MFR_SPECIAL_ID (device identification)

  • MFR_VOUT_PEAK, MFR_IOUT_PEAK, MFR_VIN_PEAK

  • MFR_CLEAR_PEAKS, MFR_ADC_CONTROL

  • MFR_PWM_MODE, MFR_PWM_COMP

  • Store/restore user settings

Data Formats

LINEAR11 Format:

  • 5-bit signed exponent + 11-bit signed mantissa

  • Used for: current, power, temperature, time values

LINEAR16 Format:

  • Fixed exponent (-12) + 16-bit mantissa

  • Used for: voltage values (VOUT_COMMAND, READ_VOUT)

Channel Configuration

The LTM4700 supports dual-channel operation:

  • Channel 0: VOUT0, IOUT0, POUT0

  • Channel 1: VOUT1, IOUT1, POUT1

  • Global: VIN, IIN, PIN, temperatures

Pages are used to select channels for PMBus commands.

IIO Integration

The driver provides comprehensive IIO (Industrial I/O) support:

IIO Channels:

  • vin: Input voltage monitoring

  • vout0/vout1: Output voltage monitoring and control

  • iin: Input current monitoring

  • iout0/iout1: Output current monitoring

  • pin: Input power monitoring

  • pout0/pout1: Output power monitoring

  • temp0/temp1: Temperature monitoring

  • frequency0/frequency1: Switching frequency

IIO Attributes:

  • raw: Read telemetry values

  • command: Set output voltage

  • operation: Control channel operation mode

  • clear_peaks: Reset peak value tracking

  • device_id: Device variant identification

Usage Example

Basic device initialization:

struct ltm4700_init_param init_param = {
    .i2c_init = &i2c_init_param,
    .crc_en = false
};

struct ltm4700_dev *dev;
int ret = ltm4700_init(&dev, &init_param);

Reading telemetry:

int vin_mv, vout0_mv, iout0_ma;

// Read input voltage in millivolts
ltm4700_read_value(dev, 0, LTM4700_VIN, &vin_mv);

// Read output voltage for channel 0
ltm4700_read_value(dev, 0, LTM4700_VOUT, &vout0_mv);

// Read output current for channel 0
ltm4700_read_value(dev, 0, LTM4700_IOUT, &iout0_ma);

Setting output voltage:

// Set VOUT0 to 1.2V (1200mV)
ltm4700_vout_value(dev, 0, 1200000, 1800000); // command, max

// Set operation mode
ltm4700_set_operation(dev, 0, LTM4700_OPERATION_ON);

IIO Usage:

struct ltm4700_iio_desc *iio_desc;
struct ltm4700_iio_desc_init_param iio_init_param = {
    .ltm4700_init_param = &ltm4700_init_param
};

ltm4700_iio_init(&iio_desc, &iio_init_param);

Status monitoring:

struct ltm4700_status status;
ltm4700_read_status(dev, 0, LTM4700_STATUS_ALL_TYPE, &status);

if (status.vout & VOUT_OV_FAULT)
    printf("Output overvoltage fault detected\n");

Design Considerations

Power Supply Design:

  • Provide adequate input capacitance for transient response

  • Follow recommended PCB layout guidelines

  • Consider thermal management for high current operation

I2C Interface:

  • Use appropriate pull-up resistors (1kΩ - 10kΩ)

  • Keep trace lengths short for high-speed operation

  • Consider CRC protection for noisy environments

Dual Channel Operation:

  • Channels can operate independently or in current sharing mode

  • Use PAGE command to select channel for configuration

  • Monitor both channels for fault conditions

Fault Management:

  • Implement appropriate fault handling in application

  • Use status registers to identify fault conditions

  • Consider automated recovery strategies

Build Configuration

Add the LTM4700 driver to your project by including in src.mk:

SRCS += $(DRIVERS)/power/ltm4700/ltm4700.c

For IIO support, also include:

SRCS += $(DRIVERS)/power/ltm4700/iio_ltm4700.c \
        $(LIBRARIES)/iio/iio.c
Dependencies:

  • I2C platform driver

  • no-OS utility functions

  • CRC8 library (if CRC enabled)

  • IIO framework (for IIO support)