# XT4051K421MR-G

**NATLINEAR** · Battery Management ICs · SOT-23-5L

XT4051K421MR-G from NATLINEAR, in a SOT-23-5L. Pinout and pin descriptions extracted from the manufacturer datasheet (extract_pins, cross-checked by a second model); symbol, footprint, and 3D from KiCad-official CAD.

## Pinout

| Pin | Name | Type | Function |
|---|---|---|---|
| 1 | CHRG | output | Open-drain charge status output that is pulled low by an internal N-channel MOSFET while charging and is high-impedance when charging is complete or during undervoltage lockout; a 1µF capacitor between BAT and GND lets the pin flag a missing battery by fast LED blinking. |
| 2 | GND | power_in | Ground pin. |
| 3 | BAT | power_out | Charge current output that supplies current to the battery and regulates the float voltage to 4.2V, with an internal precision resistor separating this pin from the auto-shutdown float voltage; with a reversed battery, about 0.7mA flows between GND and BAT while the internal protection limits damage to the ESD diode. |
| 4 | VCC | power_in | Positive input supply for the charger, specified from 4.25V to 6.5V, which must be bypassed with at least 1µF; if VCC falls to within 100mV of the BAT voltage the device enters standby and BAT current drops below 2µA. |
| 5 | PROG | bidirectional | Charge current programming, monitoring and shutdown pin, where a 1% resistor to ground sets the charge current via IBAT = (VPROG/RPROG)×200, the pin holds 1V in constant-current mode, reaching 1.21V shuts the charger down, and pulling above the approximately 2.4V pinch-off voltage draws about 1.5mA. |

## Key specifications

| Parameter | Value |
|---|---|
| Manufacturer | NATLINEAR |
| Package | SOT-23-5L |
| Category | Power Management ICs |
| Pins | 5 |

## Electrical characteristics

Limits as printed in the datasheet (page.json `metadata.characteristics` carries them as data).

| Parameter | Symbol | Min | Typ | Max | Unit | Conditions | Page |
|---|---|---|---|---|---|---|---|
| Input voltage | Vcc | 4.25 |  | 6.5 | V |  | 4 |
| Output control voltage (float) | Vfloat | 4.158 | 4.2 | 4.342 | V | 0℃<TA<85℃, IBAT = 40mA | 4 |
| BAT pin current, current mode | Ibat | 18 | 20 | 22 | mA | Rprog=10k, Current mode | 4 |
| BAT pin current, current mode | Ibat | 93 | 100 | 107 | mA | Rprog=2k, Current mode | 4 |
| BAT pin current, standby mode | Ibat | 0 | -2.5 | -6 | µA | Standby mode, Vbat=4.2V | 4 |
| Trickle charge current | Itrikl | 18 | 20 | 22 | mA | Vbat<Vtrikl, Rprog=2k | 4 |
| Trickle charge threshold voltage | Vtrikl | 2.8 | 2.9 | 3 | V | Rprog=10K, Vbat Rising | 4 |
| Trickle charge hysteresis voltage | Vtrhys | 50 | 75 | 100 | mV | Rporg=10k (as printed) | 4 |
| Undervoltage lockout threshold voltage | Vuv | 3.7 | 3.8 | 3.93 | V | From Vcc low to high | 4 |
| Undervoltage lockout hysteresis voltage | Vuvhys | 80 | 115 | 150 | mV |  | 4 |
| Manual shutdown threshold voltage (PROG rising) | Vmsd | 1.15 | 1.21 | 1.3 | V | PROG pin rising | 4 |
| Manual shutdown threshold voltage (PROG falling) | Vmsd | 0.9 | 1 | 1.1 | V | PROG pin falling | 4 |
| Vcc-Vbat stop-working threshold voltage (low to high) | Vasd | 140 | 220 | 300 | mV | Vcc from low to high | 4 |
| Vcc-Vbat stop-working threshold voltage (high to low) | Vasd | 80 | 120 | 160 | mV | Vcc from high to low | 4 |
| C/10 termination threshold current | Iterm | 0.255 | 0.3 | 0.345 | mA/mA | Rprog=10k | 4 |
| PROG pin voltage | Vprog | 0.93 | 1 | 1.07 | V | Rprog=10k, Current mode | 4 |
| CHRG weak pull-down current | Ichrg | 8 | 20 | 35 | µA | Vchrg=5V | 4 |
| Input voltage (absolute maximum, Vcc) | Vcc | -0.3 |  | 7 | V | Printed as VSS-0.3 to VSS+7 V (min relative to VSS) | 3 |
| PROG pin voltage (absolute maximum) | Vprog | -0.3 |  |  | V | Printed as VSS-0.3 to Vcc+0.3 V; max not a fixed number | 3 |
| BAT pin voltage (absolute maximum) | Vbat | -0.3 |  | 7 | V | Printed as Vss-0.3 to 7 V | 3 |
| CHRG pin voltage (absolute maximum) | Vchrg | -0.3 |  | 10 | V | Printed as VSS-0.3 to VSS+10 V (min relative to VSS) | 3 |
| Power dissipation | PD |  |  | 250 | mW | SOT-23-5L package | 3 |
| BAT pin current | Ibat |  |  | 200 | mA |  | 3 |
| PROG pin current | Iprog |  |  | 800 | uA |  | 3 |
| ESD capability, human body model | VESD |  |  | 7000 | V | Human body model | 3 |
| Operating ambient temperature | Topa | -40 |  | 85 | °C |  | 3 |
| Storage temperature | Tstr | -65 |  | 125 | °C |  | 3 |

## CAD (KiCad official)

- Symbol: `XT4051K421MR-G`
- Footprint: `Package_TO_SOT_SMD:SOT-23-5`
- 3D model: SOT-23-5L (KiCad packages3D, STEP)
- 3D model files: `xt4051k421mr-g-etched.step` / `xt4051k421mr-g-etched.glb` carry the MPN laser-etched on the die in a toggleable `Adom.LaserEtch` group (Fusion-ready); `xt4051k421mr-g.step` / `xt4051k421mr-g.glb` are the bare package body.

## Provenance

Data extracted from the manufacturer datasheet, not a distributor listing:

- **Datasheet:** [NATLINEAR datasheet](docs/xt4051k421mr-g-datasheet.pdf) (11 pp, sha256 `a0f7650ff6f486f8`, retrieved 2026-10-29, tier: lcsc)
- **Datasheet language:** Chinese. Pin names, descriptions, and specs on this page were extracted and translated to English by ds2sf; the linked PDF is the manufacturer original.
- **Extractor:** parts-factory `2.0.0` / `extract_pins 0.3`, primary `claude-haiku-5-5` (text), consensus `claude-sonnet-5-5` (agreed), guards: pin_guards 0.1: passed. Pins are checked against the footprint pad set and their cited datasheet pages before publish.
- **CAD:** KiCad official libraries (CC-BY-SA 4.0).

[Datasheet PDF](docs/xt4051k421mr-g-datasheet.pdf)