EMI Certified Step-Down Converter in 15mm × 9mm μModule Package Produces 1A, 0.8V_OUT – 10V_OUT from 3.6V_IN – 36V_IN

by David Ng

2009-12-01

570.72 K

Introduction

The LTM8031 is a low noise DC/DC step-down μModule regulator that operates from input voltages from 3.6V to 36V and is independently certified to be compliant with the stringent requirements of EN55022 class B. Its output can be programmed to provide voltages from 0.8V to 10V at up to 1A. A nearly complete converter solution is contained in the 15mm × 9mm × 2.82mm package. As seen in Figure 1, the LTM8031 just requires one resistor to set the output voltage, another resistor to set the operating frequency, and some input and output capacitance.

Figure 1. The LTM8031 needs just two resistors and some capacitance to get it running.

LTM8031 Features

The LTM8031 comes with many of the features often required in modern power supplies. It can be sequenced via its RUN/SS pin, which also serves to allow the user to control the output behavior at turn on. A PGOOD pin indicates when the output is within 10% of the target regulation voltage. The SYNC pin is used to synchronize the LTM8031 to a desired system frequency.

Through the incorporation of a high Q pi filter and electromagnetic interference reduction design techniques, the LTM8031 is purpose built with low radiated emissions in mind. It has been independently verified to be compliant with EN55022:2006 (Information Technology Equipment – Radio Disturbance Characteristics – Limits and Methods of Measurement). EN55022 has two classes, A and B. The LTM8031 is certified compliant with class B, the more stringent of the two. More than that, the LTM8031 beats the EN55022B limits by a wide margin, better than 20dB in some bands. This is shown in Figures 2, 3 and 4, where the LTM8031 is operated from 36V_IN to produce 10V_OUT, 5V_OUT and 2.5V_OUT at 1A, respectively. The 36V_IN, 10V_OUT at 1A configuration is a worst case radiated emissions scenario, because the LTM8031 is operating with both maximum rated switching voltage and output power.

Figure 2. The LTM8031 meets EN55022 Class B while producing 10V_OUT at 1A from 36V_IN.

Figure 3. The LTM8031 is EN55022 Class B compliant with 5V_OUT at 1A from 36V_IN.

Figure 4. The LTM8031 beats the EN55022 Class B limits by a wide margin with 2.5V_OUT at 1A from 36V_IN.

The LTM8031 is rated to provide 1A, but what about other load currents? Analog Devices offers three other EN55022 class B compliant μModule DC/DC converters, as well: the LTM8020 for 200mA loads, the LTM8021 for 500mA, and the LTM8032 for 2A loads. These are summarized in Table 1, and the worst case emissions for each are given in Figures 5, 6, and 7, respectively.

Table 1. Low noise μModule DC/DC step down converters
Product	V_IN Range	V_OUT Range	I_LOAD(MAX)
LTM8020	4V to 36V	1.25V to 5V	200mA
LTM8021	3.6V to 36V	0.8V to 5V	500mA
LTM8031	3.6V to 36V	0.8V to 10V	1A
LTM8032	3.6V to 36V	0.8V to 10V	2A

Figure 5. The LTM8020 is our quietest EMC μModule converter, providing 5V at 200mA from 36V_IN.

Figure 6. The LTM8021 is another EN55022B compliant device, capable of outputting 5V at 500mA from 36V_IN.

Figure 7. The LTM8032, weighing in at 10V_OUT at 2A from 36V_IN, meets EN55022 class B.

Conclusion

It is not uncommon to have to design a power system that requires numerous power rails at different load currents, low radiated emissions, and small size. For ease of design, take a look at the LTM8031 and its family of low noise μModule DC/DC step-down converters.