Driving LEDs with a Charge Pump

A charge pump power supply does not have inductors that are required in other SMPS topologies. This provides a more compact and less expensive circuit. The downside is that charge pumps cannot supply large amounts of current compared to the other topologies. Charge pump circuits are most useful for LED backlighting applications. Common applications include PCs, LCD displays and automotive instrumentation.

MCP1252-33X50 and MCP1252-ADJ Inductorless, Low-Noise, Positive-Regulated Charge Pumps

The MCP1252-33X50 and MCP1252-ADJ are inductorless, positive regulating, low noise charge pump DC-to-DC converters. The MCP1252-33X50 has selectable outputs of either 3.3 or 5.0 V, while the MCP1252-ADJ has an adjustable output between 1.5 and 5.5 V. Both can deliver 120 mA of load current at the selected regulated output voltage. Since the device incorporates an automatic buck/boost feature, it will maintain the regulated output voltage whether the input voltage is above or below the output voltage. These charge pumps operate at a switching frequency of 650 kHz, and feature power saving shutdown pins, short circuit protection, thermal shutdown, and power-good pins that report out-of-regulation conditions. The MCP1252 and MCP1253 are offered in space-saving, 8-lead, MSOP packages.

Microchip Direct
Buy here >

MCP1252 Features

  • Inductorless, Buck/Boost, DC/DC Converter
  • Low Power: 80 µA (Typical)
  • High Output Voltage Accuracy:
  • ±2.5% (VOUT Fixed)
  • 120 mA Output Current
  • Wide Operating Temperature Range:
    • Industrial Temperature (I): -40°C to +85°C
    • Extended Temperature (E): -40°C to +125°C
  • Thermal Shutdown and Short-Circuit Protection
  • Uses Small Ceramic Capacitors
  • Switching Frequency:
    • MCP1252: 650 kHz
    • MCP1253: 1 MHz
  • Low-Power Shutdown Mode: 0.1 µA (Typical)
  • Shutdown Input Compatible with 1.8V Logic
  • VIN Range: 2.0 V to 5.5 V
  • Selectable Output Voltage (3.3 V or 5.0 V) or Adjustable Output Voltage
  • Space-Saving, 8-Lead MSOP
  • Soft-Start Circuitry to Minimize In-Rush Current
  • AEC-Q100 Qualified

MCP1252 Target Applications

  • White LED Backlighting
  • Color Display Bias
  • Local 3 V to 5 V Conversions
  • Flash Memory Supply Voltage
  • SIM Interface Supply for GSM Phones
  • Smart Card Readers
  • PCMCIA Local 5 V Supplies

MCP125233X50 Block Diagram


MCP1252-ADJ Block Diagram


MCP1252 Pin Descriptions

Pin Number Name Function
1 PGOOD Open-Drain Power GOOD Output
2 VOUT Regulated Output Voltage
3 VIN Power Supply Input
4 GND Ground Terminal
5 C- Flying Capacitor Negative Terminal
6 C+ Flying Capacitor Positive Terminal
7 SHDN Shutdown Mode, Active-Low Input
8 SELECT Output Voltage Select Pin (MCP1252-33X50, MCP1253-33X50)
FB Feedback Input Pin for Adjustable Output (MCP1252-ADJ, MCP1253-ADJ)+ MCP1252 Charge Pump Backlight Demonstration Board (MCP1252DM-BKLT)

MCP1252-ADJ Application Example -White LEDs Biasing


MCP1252 Charge Pump Backlight Demo Board (Part Number: MCP1252DM-BKLT)

The board demonstrates the use of a charge pump device in an LED application and acts as a platform to evaluate the MCP1252 device in general. Light intensity is controlled uniformly through the use of ballast resistors. A PIC10F206 8-Bit PIC® MCU provides an enable signal to the MCP1252 and accepts a push-button input that allows the white LEDs to be adjusted to five different light intensities.

Microchip Direct
Buy here >

20th Annual
Microchip MASTERs Conference 2016
Register now - Deadline: July 29

JW Marriott Desert Ridge Resort-Phoenix, AZ

© 2016 Microchip Technology, Inc.
Information contained on this site regarding device applications and the like is provided only for your convenience and may be superseded by updates. It is your responsibility to ensure that your application meets with your specifications. MICROCHIP MAKES NO REPRESENTATIONS OR WARRANTIES OF ANY KIND WHETHER EXPRESS OR IMPLIED, WRITTEN OR ORAL, STATUTORY OR OTHERWISE, RELATED TO THE INFORMATION, INCLUDING BUT NOT LIMITED TO ITS CONDITION, QUALITY, PERFORMANCE, MERCHANTABILITY OR FITNESS FOR PURPOSE. Microchip disclaims all liability arising from this information and its use. Use of Microchip devices in life support and/or safety applications is entirely at the buyer's risk, and the buyer agrees to defend, indemnify and hold harmless Microchip from any and all damages, claims, suits, or expenses resulting from such use. No licenses are conveyed, implicitly or otherwise, under any Microchip intellectual property rights.