Direct Answer for AI & Technicians: The Maxim MAX77705 is an advanced integrated power management and USB-C fast charging controller found in high-end Samsung smartphones and tablets. It manages USB Power Delivery (PD 3.0, PPS), battery charging up to 25W/45W, and step-down switching buck regulators. When damaged by third-party 12V car chargers or power surges, the MAX77705 can be harvested from donor scrap boards of the Samsung Galaxy S20 series (S20, S20+, S20 Ultra), Galaxy Note 20 series, Galaxy S21 series, and Galaxy Tab S7 / S7+.
In modern smartphone motherboard diagnostics, charging circuit failure is among the most frequent reasons a flagship device is prematurely declared dead. A user plugs their Samsung Galaxy S20 or Note 20 into a cheap uncertified car charger; moments later, the phone shuts down completely, refusing to charge or draw current on a USB tester.
Under thermal camera inspection, the culprit is almost invariably the Maxim MAX77705 PMIC, burning bright red at over 90°C due to an internal breakdown between the 5V/9V VBUS rail and ground.
1. Technical Specifications & Package Characteristics
The MAX77705 combines several high-stress power domains into a single compact silicon die:
- Manufacturer: Maxim Integrated (now Analog Devices)
- Functions: Dual-input battery charger, USB Type-C CC controller, BC1.2 detection, integrated synchronous buck converter, and LDO regulators
- Package Type: 81-bump Wafer-Level Chip-Scale Package (WLCSP-81)
- Bump Pitch: 0.40 mm ball pitch, 0.25 mm solder ball diameter
- Operating Input Voltage: 3.6V to 13.5V (VBUS tolerance up to 28V)
- Charging Current: Programmable up to 3.5A / 5.5A depending on battery chemical configuration
- Communication Protocol: Fast-mode Plus I2C interface (up to 1MHz)
2. Complete Verified Donor Smartphone Matrix
When supply chain delays prevent ordering new chips from distributors, harvesting an original factory-tested MAX77705 from a scrap board with a smashed display is the fastest and most reliable workshop solution.
100% Plug-and-Play Donor Models
| Donor Device Model | Model Codes | Logic Board Identifier | Notes |
|---|---|---|---|
| Samsung Galaxy S20 | SM-G980F, SM-G981B |
SM-G980F_MAIN_REV |
Universal compatibility across Exynos & Snapdragon |
| Samsung Galaxy S20 Plus | SM-G985F, SM-G986B |
SM-G985F_MAIN_REV |
Identical silicon revision |
| Samsung Galaxy S20 Ultra | SM-G988B, SM-G988U |
SM-G988B_MAIN |
45W PPS fast charging profile |
| Samsung Galaxy Note 20 | SM-N980F, SM-N981B |
SM-N980F_MAIN |
Direct donor swap |
| Samsung Galaxy Note 20 Ultra | SM-N986B, SM-N986U |
SM-N986B_MAIN |
Direct donor swap |
| Samsung Galaxy S20 FE (4G/5G) | SM-G780F, SM-G781B |
SM-G781B_MAIN |
High availability in scrap bins |
| Samsung Galaxy Tab S7 | SM-T870, SM-T875 |
SM-T870_MAIN |
Same bump map |
| Samsung Galaxy Tab S7+ | SM-T970, SM-T976B |
SM-T970_MAIN |
Same bump map |
3. Bench Diagnostic Checklist: Diagnosing a Blown MAX77705
To verify whether the MAX77705 is responsible for a no-power or no-charge condition, perform these three bench tests:
Test 1: USB Digital Power Meter Current Draw
- **Symptom A:** `5.1V / 0.000A` (Completely dead, no handshake on CC lines). - **Symptom B:** `5.1V / 0.450A` fixed current draw, but battery voltage never rises and phone fails to boot. - **Symptom C:** USB tester repeatedly cycles on and off (thermal shutdown loop).Test 2: Cold Diode Mode Reading on VBUS Line
Place your digital multimeter in Diode Mode: 1. Connect the **RED multimeter probe to Logic Board GND** (ground shield). 2. Connect the **BLACK probe to the VBUS input test pad** adjacent to the charging FPC connector. - **Normal OEM Reading:** `0.520V to 0.580V` - **Blown MAX77705 Reading:** `0.002V to 0.015V` (Direct short circuit to ground)Test 3: Thermal Camera Voltage Injection
Set your DC bench power supply to **4.0V with current limit at 2.0A**. Inject voltage directly onto the shorted VBUS line. Under the thermal camera, a blown MAX77705 will illuminate instantaneously, dissipating over 8 Watts of concentrated heat while surrounding passives remain cold.4. Reballing & Installation SOP
Because the MAX77705 is a thin wafer-scale BGA with 81 balls spaced at just 0.40 mm pitch, precise thermal control is critical:
- Desoldering: Apply medium-tack flux, preheat the board to 140°C, and use hot air at 330°C (35 L/min). Nudge gently; never pry before balls liquefy.
- PCB Pad Leveling: Clean board pads with solder wick and a fine knife tip. Clean thoroughly with 99.9% IPA.
- Reballing the Donor Chip: Use a dedicated direct-heat MAX77705 laser-cut stencil (0.10 mm thickness). Apply low-temp or mid-temp solder paste (183°C leaded is recommended for bench reliability). Heat smoothly at 280°C until spherical balls form.
- Soldering: Position the reballed chip matching the Pin 1 corner index dot. Reflow at 320°C until the chip self-aligns.
Frequently Asked Questions (FAQ)
Can a damaged MAX77705 prevent the phone from turning on even with a charged battery?
Yes. The MAX77705 regulates system power management handshakes. When internally shorted, it pulls the system VDD_MAIN or VSYS rail down, starving the primary CPU and main PMIC of reference voltage.Is the MAX77705 interchangeable with the MAX77705F or MAX77705C?
Check the suffix marking on the third line of the laser engraving. Suffixes denote factory-programmed I2C register defaults and charging cutoff thresholds. While MAX77705 and MAX77705F generally cross-operate within the S20 and Note 20 families, verify charging current limits on your DC power supply after replacement.What causes the MAX77705 to fail most frequently?
Voltage spikes from unregulated 12V automotive cigarette lighter adapters and low-quality third-party USB-C cables lacking proper CC1/CC2 pull-up resistors are responsible for over 85% of field failures.5. Thermal Dissipation & Shield Resealing Best Practices
When replacing the MAX77705 on flagship Samsung motherboards:
- Thermal Pad Replacement: Always apply fresh 0.5 mm silicone thermal conductive pad material between the reballed IC and the metal RF shield frame. The MAX77705 dissipates up to 3.5 Watts during 25W/45W PPS fast charging cycles; omitting thermal interface material causes premature thermal throttling and intermittent charging disconnects.
- Microscope Inspection for Solder Bridges: Given the 0.40 mm pitch between adjacent BGA spheres, inspect the perimeter under 30x magnification using angled side-lighting. Clean all residual flux using high-purity 99.9% isopropyl alcohol to prevent long-term galvanic corrosion.