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Low EMC Charge Pump for Supply System

IP.com Disclosure Number: IPCOM000131955D
Published in the IP.com Journal: Volume 5 Issue 12A (2005-12-25)
Included in the Prior Art Database: 2005-Dec-25
Document File: 5 page(s) / 56K

Publishing Venue

Siemens

Related People

Juergen Carstens: CONTACT

Abstract

The problem to be solved is to reduce EMC (Electromagnetic Compatibility) caused by charge pump versus Battery (clean supply) in a supply system. In Figure1 is shown a typical supply system. The main input is IN1 where a battery (or a shared supply) is connected. A pre-regulator block generates the IN2 supply voltage. IN2 is the supply for most of the other parts of the system (i.e. some post regulators). Inside automotive supply systems, it becomes more and more important to switch on the entire system at battery voltages, which are continuously lower. Therefore a start up booster (i.e. a charge pump) is needed (as shown in Figure 2) to start-up at low battery the pre-regulator (and when needed also the post regulators Post-reg1 … Post-regn). Charge pumps are strong EMI (Electromagnetic Interference) emitters and the battery (or a shared supply that it is named IN1) needs during normal operation to be as clean as possible because of other devices are connected to that line. It is therefore mandatory reducing or, if possible, avoiding injection of disturbances into battery. It means that since efficient boost converter (e.g. a charge pump) is necessary inside the power system, because of the switching nature of those high efficiency converters, it becomes important to avoid or to limit injection of disturbances into Battery.

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Low EMC Charge Pump for Supply System

Idea: Christian Garbossa, IT-Padova; Marco Flaibani, IT-Padova; Emanuele Bodano, IT-Padova

The problem to be solved is to reduce EMC (Electromagnetic Compatibility) caused by charge pump versus Battery (clean supply) in a supply system. In Figure1 is shown a typical supply system. The main input is IN1 where a battery (or a shared supply) is connected. A pre-regulator block generates the IN2 supply voltage. IN2 is the supply for most of the other parts of the system (i.e. some post regulators). Inside automotive supply systems, it becomes more and more important to switch on the entire system at battery voltages, which are continuously lower. Therefore a start up booster (i.e. a charge pump) is needed (as shown in Figure 2) to start-up at low battery the pre-regulator (and when needed also the post regulators Post-reg1 ... Post-regn). Charge pumps are strong EMI (Electromagnetic Interference) emitters and the battery (or a shared supply that it is named IN1) needs during normal operation to be as clean as possible because of other devices are connected to that line.

It is therefore mandatory reducing or, if possible, avoiding injection of disturbances into battery. It means that since efficient boost converter (e.g. a charge pump) is necessary inside the power system, because of the switching nature of those high efficiency converters, it becomes important to avoid or to limit injection of disturbances into Battery.

In the past, EMI interferences caused by charge pumps used in supply systems have been solved with external filtering (e.g. PI filters, that means high cost for customer especially for high frequency) or with integrated solutions that complicate the design and require area overhead. For instance, in some previous works (see Figure 3) two different charge pumps have been employed: a low-current one CP1 (that inject low EMI to IN1) used only for startup reasons, and another one CP2 supplied for IN2 capable to deliver a higher current for normal operation. Disadvantage of this last approach is again area overhead and a residual EMI injection of the low current charge pump always active.

With the following idea the problem of EMI injection into Battery is solved using only one charge pump as shown in Figure 4, sensing the pre-regulated voltage IN2 (by comparator S) generated inside the overall system supply and controlling the input switches (SW1 and SW2) of the charge pump supply accordingly. It is possible, therefore, to limit EMI injection only during startup phase (when SW1 is closed and SW2 is open), while eliminating disturbances during normal operation (when SW2 is closed and SW2 is open). To do the job it is needed a comparator t...