Backup power supply circuits (DUL)

Info Box Applies to DUL

Introduction

The concept schematic here described provides some hints about possible implementations of backup power supply for DUL module.

Four different options are shown, based on capacitors or battery. These are briefly described in the following sections.

Two options are provided for main power supply (5V): it can be connected to USB VBUS (USB_VBUS) or to external power supply (EXT_5V) via J22 jumper.

Main power supply is used to charge auxiliary energy storage device via J23.

J24 is used to select which energy storage device is connected to backup power supply input of DUL.

J19 is reference of LCC-68 socket where DUL can be plugged. MOD1 is reference of DUL module when soldered on PCB directly. R25, R26, R28 and R31 allow to connect USB bus to socket or soldered-down DUL module.

DL5, DL6, DL7 and DL8 are staus LEDs connected rispectively to the following signals of DUL:

• STAT2#
• WARN#
• STAT1#
• LED_0

J18 and J20 are provided to enable read-only modes as described here.

Options #1: supercap

First option uses a couple of 2.5V supercap. The circuit is based on a Linear Technology LTC4425 (Linear SuperCap Charger with Current-Limited Ideal Diode and V/I Monitor) for the charge of the supercaps.

The circuit is configurable with some setting jumpers:

- J2 Enable/Disable the IC
- J3 Select Normal or LDO mode
- J4 Select the maximum charge voltage for the supercap stack
- J5 Select the maximum charge current

J1 is a connector for an external supercap. The resistors R2/R3 select the input Vin failure voltage. Led diode DL1 is a power-fail indicator. When Vin il lower then the supercap stack voltage or when the supercaps aren't charge the led is ON.

Suggested part number for supercaps: COOPER Bussmann B0810-2R5105-R

See Linear Technologt LTC4425 datasheet for any other information.

Schematics

http://www.dave.eu/download/restricted/ssd/dul/DUL-EVB-0.9.1.pdf