Backup power supply circuits (DUL)
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Contents
Introduction[edit | edit source]
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 respectively 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[edit | edit source]
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.
Options #2: bestcap[edit | edit source]
Second option use a Bestcap and a resistor/diode circuit for the charge. Resistor R12 limit the maximum charge current and D2 isolate the Bestcap when the Main PSU fails.
Suggested part number for Bestcap: AVX BZ015A104ZS
Options #3: NiMH/NiCd battery[edit | edit source]
Third option use a battery pack with 2 NiMH cell in series. The IC charger is a Linear Technologt LTC4060. J9 is a connector for an external NTC thermistor (10k) for temperature control of the battery during the charge.
Setup jumpers:
- J10 Set the time charge - J11 Select the battery type, NiMH or NiCd - J12 Select the maximum charge voltage (1.2V or 1.3V) - J13 Select the maximum charge current
Led diode DL2 indicate the battery charging and DL3 is ON when Vin is greater than the undervoltage lockout threshold.
See Linear Technologt LTC4060 datasheet for any other information.
Options #4: Li-ion/Li-Po battery[edit | edit source]
Microchip MCP73831 is a single Cell, fully integrated Li-Ion or Li-Polymer charger. J16 is a settings jumper, it regulates the maximum charge current. Led DL4 is ON when the battery is in charging.
See Microchip MCP73831 datasheet for any other information.
Schematics[edit | edit source]
Following link provides conceptual schematics of an evaluation board implementing some solutions for the auxiliary power supply. Please note that these schematics do not refer to an actual board that has been manufactured.
