Negative charge pump

• US 20050077950A1
• Filed: 10/14/2003
• Published: 04/14/2005
• Est. Priority Date: 10/14/2003
• Status: Abandoned Application

• Current Assignee: Monolithic Power Systems Incorporated
• Original Assignee: Monolithic Power Systems Incorporated
• Inventors: Robinson, Curtis B. Jr.
• Application Number:
  US10/685,132
• Publication Number:
  US 20050077950A1
• Time in Patent Office: Days
• US Class Current: 327/536
• CPC Class Codes: H02M 1/36 Means for starting or stopping converters
• CPC Class Codes: H02M 3/07 using capacitors charged and discharged alternately by semiconductor devices with control electrode , e.g. charge pumps
• CPC Class Codes: H02M 3/071 adapted to generate a negative voltage output from a positive voltage source

Abstract

A negative charge pump is disclosed. The negative charge pump may be used to drive white LEDs in one application. The negative charge pump uses predominantly n-channel transistor switches that enables a smaller integrated circuit area. Further, a soft start mechanism is used in starting the charge pump.

Claims

1. A negative charge pump formed on a semiconductor substrate comprising:

a power supply having a first terminal connected to said substrate and a second terminal connected to a high voltage rail;

a plurality of charging capacitors connected between said high voltage rail and said substrate, said charging capacitors connected to said high voltage rail by a first set of transistor switches and connected to said substrate by a second set of transistor switches;

an output capacitor connected between said high voltage rail and said charging capacitors, said output capacitor connected to at least one of the said charging capacitors by a third set of transistor switches;

wherein said second and third sets of switches are NMOS transistors and said first set of switches are PMOS switches.

2. The negative charge pump of claim 1 further including a supervisory circuit operative in a shutdown mode to catch the output voltage to said negative supply voltage.

3. The negative charge pump of claim 1 wherein at least one of said second set of switches is formed from a plurality of transistors that are staggered in switching on during a soft start mode.