## MIC79110: High-Accuracy Linear Li-Ion Battery Charger The **MIC79110** is a simple yet highly accurate fixed-voltage linear battery charger designed for single-cell Lithium-Ion (Li-Ion) batteries. It is part of the Microchip (formerly Micrel) family of power management ICs, known for its small footprint and minimal external component requirements. --- ### 1. Key Technical Specifications | Parameter | Specification | |:---|:---| | **Input Voltage Range** | 4.5V to 16V | | **Output Voltage (Fixed)** | 4.2V (standard Li-Ion) | | **Regulation Accuracy** | ±0.75% over temperature | | **Max Charge Current** | Up to 1.2A (limited by thermal dissipation) | | **Package Types** | SOIC-8, MSOP-8 | | **Operating Temperature** | -40°C to +125°C | --- ### 2. Core Functional Parts The internal architecture of the MIC79110 consists of several critical electronic sub-systems: #### A. The Pass Transistor Unlike switching regulators that use inductors, the MIC79110 uses an internal **P-channel MOSFET** as a linear pass element. It acts like a variable resistor that drops the input voltage down to the battery voltage. #### B. Precision Voltage Reference To ensure battery safety and longevity, the chip features a high-precision bandgap reference. The **±0.75% accuracy** is crucial because overcharging a Li-Ion cell by even 50mV can significantly reduce its cycle life or cause instability. #### C. Control Logic (Charge Stages) The device manages the two primary stages of Li-Ion charging: 1. **Constant Current (CC):** The IC limits the current to a level set by the external components to safely bulk-charge the battery. 2. **Constant Voltage (CV):** As the battery nears 4.2V, the IC maintains a precise voltage while the current naturally tapers off. #### D. Thermal Shutdown & Protection Since linear chargers dissipate heat (Power = $(V_{in} - V_{out}) \times I_{charge}$), the MIC79110 includes **thermal limiting**. If the die temperature exceeds roughly 160°C, the device reduces the charging current to prevent damage. --- ### 3. Pin Configuration and Functions | Pin Number | Name | Description | |:---|:---|:---| | 1 | **BATT** | Output to the positive terminal of the battery. | | 2 | **VCC** | Input supply voltage. | | 3 | **NC** | No internal connection. | | 4 | **GND** | Ground reference. | | 5 | **EN** | Enable pin; pull high to activate charging, low to shut down. | | 6 | **ISET** | Current set pin; determines the charging current via a resistor. | | 7 | **STATE** | Status output (Open collector); indicates if the battery is charging. | | 8 | **VSENSE** | Voltage sense input for Kelvin sensing at the battery terminal. | --- ### 4. Typical Application Circuit The MIC79110 is favored because it requires very few external parts: ```c // Simplified Connection Diagram [Input 5V-12V] ----> [VCC] [BATT] ----> [Battery +] | | [ MIC79110 ] | | [GND] <------------- [GND] [ISET] ----> [Resistor to GND] ``` --- ### 5. Pros and Cons **Advantages:** * **Low Noise:** No switching transitions, making it ideal for sensitive analog or RF applications. * **Simplicity:** No inductors or diodes required. * **Safety:** Built-in reverse current protection (prevents battery drain when input power is removed). **Disadvantages:** * **Efficiency:** Efficiency is low if the gap between $V_{in}$ and $V_{out}$ is large. * **Heat:** Not suitable for high-current charging if the input voltage is significantly higher than 5V.