232201 - EverTag Connectivity Module Base PCB Bat¶


Article Number	232201
Name	EverTag Connectivity Module Base PCB Bat
Base PCB	232200 Base Std
Added Feature	LiFePO4 battery backup
Status	Active

Delta Document

This document describes only the differences from the 232200 Base Std. For all shared functionality (MCU, NFC, SK6812MINI-E LED1 system status, LED2 gateway DNP, USB-C connector, service button, TC2030 debug, PCB design notes), refer to the base PCB documentation.

1. Overview¶

The 232201 adds LiFePO4 battery backup to the base 232200 connectivity module. When AC power is lost, the module automatically switches to battery power, maintaining Wirepas anchor operation for a defined hold-up period. When AC power returns, the battery is recharged automatically.

Key Features (Delta from 232200)¶

LiFePO4 battery (EEMB LP472040F) with JST-PHR-02 connector and 10cm cable
Internal voltage protection circuit (over-voltage, under-voltage, overcurrent)
Power-path management with automatic AC/battery switchover
Battery presence detection
Battery charger IC (MCP73123 -- LiFePO4 CC/CV, 3.6V cutoff)

2. Block Diagram (Delta)¶

graph TB
    subgraph power [Power Supply - Extended]
        VIN["5V Input from Power Base"] --> BUCK["TPS62160 Buck Converter"]
        BUCK --> RAIL["3.3V Rail"]

        VIN --> PPM["Power-Path Manager"]
        BAT["LiFePO4 Battery"] --> VPROT["Voltage Protection"]
        VPROT --> PPM
        PPM --> BUCK

        PPM --> CHRG["MCP73123 Charger"]
        CHRG --> VPROT
    end

    subgraph mcu_block [MCU / Radio Module]
        PAN611["PAN611 - nRF54L15"]
    end

    RAIL --> PAN611

    PAN611 -.->|"Battery presence"| PPM
    PAN611 -.->|"Battery voltage ADC"| BAT

Power-Path Operation¶

AC Power	Battery	Mode
Present	Absent	Direct 5V to regulator
Present	Present	5V powers system + charges battery
Lost	Present	Battery powers system through protection circuit
Lost	Absent	System off

3. Schematics (Delta)¶

3.1 Battery Circuit¶

EEMB LP472040F battery -- datasheet drawing with dimensions and JST connector

Battery (Article 232250)¶

Parameter	Value
Cell	EEMB LP472040F-PCM-LD
Chemistry	LiFePO4 (Lithium Iron Phosphate)
Nominal Voltage	3.2V
Capacity	330 mAh (typical, 0.2C @ 25C)
Connector	JST-PHR-02
Cable Length	10cm
Article Number	232250

Voltage Protection Circuit¶

An internal voltage protection circuit protects the battery from:

Over-voltage -- Prevents charging above safe limit
Under-voltage -- Disconnects load at minimum cell voltage
Overcurrent -- Protects against short circuit

Parameter	Value
Protection IC	Integrated in battery PCM (LP472040F-PCM-LD)
Additional board-level protection	MCP73123 OVP (6.5V input), reverse discharge

Charger IC -- MCP73123¶

Parameter	Value
IC	Microchip MCP73123-22SI/MF
Charge Voltage	3.6V (factory preset for LiFePO4)
Charge Current	Programmable via R_PROG: 130 mA to 1100 mA
Recommended I_charge	250 mA (0.5C for ~500 mAh cell, safe and fast enough)
R_PROG for 250 mA	4.0k (1%)
Input Voltage	4.15V -- 6.5V (OVP at 6.5V)
Input Source	5V from Power Base Module
End-of-Charge	10% of I_charge (25 mA)
Safety Timer	4 hours (configurable: 4/6/8 HR or disabled)
Voltage Accuracy	± 0.5%
Package	10-pin DFN (3 mm x 3 mm)
Quiescent Current	< 75 uA (standby, battery full)
Operating Temperature	-40 to +85 C
Est. Price	~$1.50 @ 10k

Charge profile: Constant Current (CC) at 250 mA until battery reaches 3.6V, then Constant Voltage (CV) at 3.6V until current drops to 25 mA (end-of-charge). The MCP73123 includes integrated reverse discharge protection, thermal regulation (junction temperature limiting), and automatic recharge at 95% of charge voltage.

graph LR
    VIN_5V["5V Input"] --> C_IN["C_IN: 4.7uF"]
    C_IN --> MCP["MCP73123"]
    MCP -->|"VBAT"| C_OUT["C_OUT: 4.7uF"]
    C_OUT --> BAT_CONN["JST S2B-PH"]

    MCP ---|"PROG pin"| R_PROG["R_PROG: 4.0k 1%"]
    R_PROG --> GND1["GND"]

    MCP -->|"STAT1"| R_LED["1k"]
    R_LED --> LED_CHG["Charge LED (optional)"]

    MCP -->|"STAT2"| MCU_STAT["nRF54 GPIO: CHARGE_STATUS"]
    MCP ---|"TE"| R_TE["Timer: 10k"]

Charge Current Programming¶

The charge current is set by a single resistor on the PROG pin:

R_PROG (1%)	Charge Current	Use Case
10k	100 mA	Slow charge, minimal heat
4.0k	250 mA	Recommended -- 0.5C for LP472040F
2.0k	500 mA	Fast charge, more heat
1.0k	1000 mA	Maximum rate (verify thermal)

Formula: I_charge = 1000V / R_PROG (where 1000V is the MCP73123 internal reference constant).

Status Pins¶

Pin	MCP73123 Pin	Direction	nRF54 GPIO	Function
STAT1	Pin 1	Output (open-drain)	P1.03 (CHARGE_ACTIVE)	Charging indicator (low = charging)
STAT2	Pin 10	Output (open-drain)	P2.04 (CHARGE_STATUS)	Charge complete (low = done)
PG	Pin 8	Output (open-drain)	P2.03 (BAT_PRESENT)	Power good (low = input valid)

Low-Cost Alternative: CN3058E

For cost-sensitive Asian production, the Consonance CN3058E ($0.13 @ 4k on LCSC, SOP-8 package) is a pin-compatible-in-function LiFePO4 charger with similar features (1A max, 3.6V cutoff, status output). However, the MCP73123 is preferred for Western production due to Microchip's long-term availability commitment and tighter voltage accuracy (± 0.5% vs ± 1.5%).

Thermal Considerations¶

At 250 mA charge current from 5V input to 3.2V battery: power dissipation = (5.0 - 3.2) x 0.25 = 0.45W
MCP73123 has internal thermal regulation -- it reduces charge current automatically if junction temperature exceeds 100C
Ensure adequate copper pour under the DFN pad (thermal pad) for heat sinking
At 0.45W, no external heatsink is needed in the enclosed design

Power-Path Management¶

The power-path circuit uses a simple ideal diode OR topology with the MCP73123 managing the charge path:

Parameter	Value
Function	Automatic switchover between AC (5V) and battery (3.2V)
AC present	5V powers TPS62160 directly; MCP73123 charges battery
AC lost	Battery 3.2V feeds TPS62160 via Schottky/ideal diode
Battery detection	MCP73123 PG pin (low = AC input valid) to nRF54 GPIO

graph LR
    VIN["5V AC"] -->|"Main path"| DIODE_AC["Ideal Diode / Schottky"]
    DIODE_AC --> V_SYS["V_SYS → TPS62160"]

    VIN --> MCP["MCP73123"]
    MCP -->|"VBAT"| BAT["Battery 3.2V"]

    BAT -->|"Backup path"| DIODE_BAT["Ideal Diode / Schottky"]
    DIODE_BAT --> V_SYS

TPS62160 Input Range

The TPS62160 operates from 3V to 17V input, so it works directly from either 5V (AC) or 3.2V (battery). At 3.2V input with 3.3V output (set by R1/R2 feedback divider), the converter operates in near-100% duty cycle mode. Verify that the 3.3V output regulates correctly with only 3.2V input -- there may be minimal dropout. If not, adjust the feedback divider for a 3.0V output rail or use an LDO bypass for battery mode.

3.2 Battery Connector¶

Parameter	Value
PCB Header	JST S2B-PH-SM4-TB(LF)(SN) -- 2-pin SMT, top-entry
Pitch	2.0 mm
Pin 1	Battery + (via protection circuit)
Pin 2	GND
Mating Connector	JST PHR-02 (on battery cable, 10 cm)
Mating Contact	JST SPH-002T-P0.5L (crimp terminal)
Current Rating	2A per contact
Est. Price (header)	~$0.10 @ 10k

JST PH Series

The JST PH series (2.0 mm pitch) is the de-facto standard for small battery connections in IoT devices. The S2B-PH-SM4-TB is the SMT variant with horizontal (top-entry) orientation, compatible with reflow soldering. The battery cable uses the mating PHR-02 housing with SPH crimp contacts -- this is the same connector system used by EEMB on the LP472040F battery.

4. Pin-Out (Delta)¶

Additional GPIO requirements beyond 232200 base pin-out:

GPIO	Function	Direction	Notes
P2.03	BAT_PRESENT	Input	MCP73123 PG pin (open-drain, 10k pull-up). LOW = AC present
P1.06	BAT_VOLTAGE	ADC Input	Battery voltage via resistor divider (SAADC AIN2)
P2.04	CHARGE_STATUS	Input	MCP73123 STAT2 (open-drain, 10k pull-up). LOW = charge done
P2.05	CHARGE_ENABLE	Output	Enable/disable charging (MCP73123 CE or power-path FET)
P1.03	CHARGE_ACTIVE	Input	MCP73123 STAT1 (open-drain, 10k pull-up). LOW = charging

Charger State Machine

The five battery GPIO signals provide full charger state visibility:

CHARGE_ACTIVE (STAT1)	CHARGE_STATUS (STAT2)	BAT_PRESENT (PG)	State
LOW	HIGH	LOW	Charging in progress
HIGH	LOW	LOW	Charge complete
HIGH	HIGH	LOW	Standby (no battery or idle)
LOW	LOW	LOW	Fault (safety timer expired)
HIGH	HIGH	HIGH	No input power (on battery)

GPIO Reserve

P1.03 (CHARGE_ACTIVE) consumes one of the two GPIO reserve pins. P1.02 remains as GPIO reserve. BAT_VOLTAGE uses P1.06 (AIN2) -- a true SAADC-capable pin in the always-configured table. All open-drain charger outputs (STAT1, STAT2, PG) require 10k pull-up resistors to 3V3.

5. Component Selection (Delta)¶

5.1 Battery¶

Parameter	Value
Manufacturer	EEMB
Part Number	LP472040F-PCM-LD
Chemistry	LiFePO4 (Lithium Iron Phosphate)
Nominal Voltage	3.2V
Article	232250
Connector	JST-PHR-02
Cable Length	10cm
Est. Price	~3--4 USD @ 5k volume

Rationale:

Thermal stability -- LiFePO4 is inherently safer than Li-ion/LiPo, reducing fire risk in permanently installed wall-powered devices
Long calendar life -- low self-discharge, 10+ year operation target
Logistics -- LiFePO4 cells are exempt from UN3480 hazardous goods classification, simplifying shipping
Lower fire risk -- critical for devices permanently mounted in occupied buildings

5.2 JST Connector (PCB Header)¶

Parameter	Value
Manufacturer	JST
Part Number	S2B-PH-SM4-TB(LF)(SN)
Series	PH (2.0 mm pitch)
Positions	2
Mount	SMT, top-entry (horizontal)
Current	2A per contact
Est. Price	~$0.10 @ 10k

Rationale: Industry-standard battery connector, reflow-compatible, mates directly with EEMB battery cable. Available from DigiKey, Mouser, and LCSC.

Supplier Links:

Source	Part Number	Notes
DigiKey	455-1749-1-ND	Western
Mouser	JST S2B-PH-SM4-TB	Western
LCSC	C160352	Low-cost

5.3 Charger IC -- MCP73123¶

Parameter	Value
Manufacturer	Microchip Technology
Part Number	MCP73123-22SI/MF
Chemistry	LiFePO4 (3.6V charge voltage)
Max Current	1100 mA (programmable via R_PROG)
Package	10-pin DFN (3 x 3 mm)
Features	OVP, thermal regulation, safety timer, auto-recharge
Est. Price	~$1.50 @ 10k