LTM4644IY: Technical Guide to Analog Devices' Dual 4A μModule Step-Down Regulator

Introduction

The LTM4644IY is a dual-output switching regulator μModule from Analog Devices, integrating two complete 4A DC-DC step-down converters in 15mm × 15mm BGA package with inductors, compensation, and power MOSFETs, delivering up to 8A total from 4V-20V input for FPGA power, multi-rail systems, and point-of-load (POL) applications.

This complete power solution simplifies multi-rail power design with two independent regulators (0.6V-5.5V output, 4A each), requiring only input/output capacitors for operation, reducing design time, PCB area, and component count compared to discrete buck converter implementations.

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Technical Overview

Core Specifications

Parameter	Specification
Input Voltage	4V to 20V
Output Voltage	0.6V to 5.5V per channel
Output Current	4A per channel (8A total)
Efficiency	Up to 92%
Switching Frequency	250kHz to 780kHz (programmable)
Package	BGA-144 (15×15mm)
Operating Temp	-40°C to +125°C

Key Features

Dual Independent Outputs:

• Two complete 4A regulators
• Independent voltage setting (0.6-5.5V)
• Separate enable controls
• Shared input, independent outputs

Complete Integration:

• Power MOSFETs (high-side and low-side)
• Inductors embedded
• Compensation network internal
• Minimal external components

Advanced Control:

• Voltage tracking capability
• Accurate current sharing
• Programmable soft-start
• Power-good indicators

High Efficiency:

• Up to 92% efficiency
• Low quiescent current
• Enhanced light-load efficiency
• Thermal shutdown protection

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Complete Specifications

Electrical Specifications

Parameter	Min	Typ	Max	Unit
Input Voltage	4	-	20	V
Output Voltage Range	0.6	-	5.5	V
Output Current (each)	-	-	4	A
Output Voltage Accuracy	-2	-	+2	%
Line Regulation	-	0.1	-	%/V
Load Regulation	-	0.2	-	%

Switching Characteristics

Parameter	Value
Switching Frequency	250kHz to 780kHz
Soft-Start Time	Programmable (0.5-10ms)
Minimum On-Time	95ns typical
Current Limit	5.5A typical per channel

Protection Features

• Overcurrent Protection: Cycle-by-cycle current limit
• Short-Circuit Protection: Hiccup mode
• Thermal Shutdown: 165°C typical
• Input Undervoltage Lockout (UVLO)
• Output Overvoltage Protection

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Applications

FPGA/ASIC Power

Multi-Rail Requirements:

VIN (12V) ──┬──► LTM4644IY CH1 ──► VCCINT (1.0V, 4A)
            │                      FPGA Core
            │
            └──► LTM4644IY CH2 ──► VCCAUX (1.8V, 3A)
                                   Auxiliary

Total: Two voltages from single module

Advantages:

• Accurate voltage regulation for FPGA
• Fast transient response
• Small PCB footprint
• Tracking/sequencing capability

Telecom/Networking

Point-of-Load (POL):

• 48V/12V to multiple lower voltages
• Distributed power architecture
• Server power delivery
• Network switch power

High Efficiency:

• Reduces heat in dense systems
• Lowers cooling requirements
• Improves reliability

Industrial Systems

Multi-Voltage Systems:

• PLC power (3.3V, 5V)
• Motor control (logic + analog supplies)
• Sensor power (isolated and non-isolated)
• HMI displays (multiple rails)

Test Equipment

Precision Supplies:

• Dual adjustable outputs
• Low noise for ADC/DAC
• Fast load response
• Programmable operation

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Design Guide

Basic Application Circuit

Minimal Configuration:

Input:
VIN (12V) ──┬── 47μF ──┬── LTM4644IY VIN
            │          │
           GND        GND

Output CH1:
VOUT1 ──┬── 47μF ──┬── Load1 (1.0V, 4A)
        │          │
       GND        GND

Output CH2:
VOUT2 ──┬── 47μF ──┬── Load2 (3.3V, 3A)
        │          │
       GND        GND

Required External:
- Input cap: 47μF (25V, ceramic/polymer)
- Output caps: 47μF each (ceramic/polymer)
- Resistors: VOUT setting dividers

Output Voltage Setting

Resistor Divider:

VOUT ──┬──► FB pin
       │
      R1 (to VOUT)
       │
      R2 (to GND)
       │
      GND

VOUT = 0.6V × (1 + R1/R2)

Example for 3.3V:
R1 = 45kΩ, R2 = 10kΩ
VOUT = 0.6V × (1 + 45k/10k) = 3.3V

Tracking and Sequencing

Voltage Tracking:

• TRACK pin allows ratio-metric tracking
• Master-slave voltage relationship
• Useful for DDR memory power

Power Sequencing:

• Independent RUN pins per channel
• Control turn-on/turn-off order
• Critical for FPGA initialization

Thermal Management

Power Dissipation:

Pdiss ≈ (VIN - VOUT) × IOUT × (1 - η)

Example:
VIN = 12V, VOUT = 1.0V, IOUT = 4A, η = 90%
Pdiss = (12-1) × 4 × 0.1 = 4.4W per channel

Total module: ~8-9W at full load

Cooling:

• Exposed pad to PCB ground plane
• Thermal vias (minimum 9 vias, 0.3mm)
• Consider heatsink for >6A total load
• Maintain junction temp <125°C

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Comparison

LTM46xx Family

Part	Outputs	Current	VIN Range	Key Feature
LTM4644IY	Dual	4A each	4-20V	Dual 4A
LTM4643	Dual	3A each	4-20V	Lower current
LTM4646	Dual	5A each	4.5-20V	Higher current
LTM4644-1	Dual	4A each	4-20V	Extended temp

μModule vs Discrete

Aspect	LTM4644IY	Discrete Buck (×2)
Design Time	<2 hours	1-2 weeks
PCB Area	225mm²	600-800mm²
Component Count	~10 external	40-50 external
Inductor	Integrated	External (×2)
Performance	Optimized	Depends on design

When to Choose LTM4644IY:

• ✅ Dual rails needed (0.6-5.5V)
• ✅ Fast time-to-market
• ✅ Limited PCB space
• ✅ Lower engineering cost
• ✅ Proven performance required

Conclusion

The LTM4644IY delivers complete dual 4A step-down regulation in compact μModule, providing two independent 0.6-5.5V outputs from 4-20V input with up to 92% efficiency. With integrated inductors, MOSFETs, and compensation, it enables rapid multi-rail power design for FPGA, POL, telecom, and industrial applications.

Key Advantages:

✅ Dual 4A Outputs: Two independent regulators in one module
✅ Complete Integration: Inductors, MOSFETs, control embedded
✅ Fast Design: <2 hours vs weeks for discrete
✅ Flexible Outputs: 0.6-5.5V per channel, independently set
✅ High Efficiency: Up to 92% reduces thermal challenges
✅ Compact: 15×15mm BGA package saves PCB space

Designing multi-rail power? Visit AiChipLink.com for technical resources and power design consultation.

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Written by Jack Elliott from AIChipLink.

 

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