FAN4855MTC - 500mA Boost Regulator, Adjustable | Fairchild
MPN: FAN4855MTC ✗ Cuối đờiFAN4855MTC Tóm tắt
A boost regulator is a type of switch-mode DC-DC converter that steps an input voltage up to a higher regulated output voltage using an inductor, a switching element, and a diode. Within the power management hierarchy, the FAN4855 sits under switching regulators, which belong to voltage regulators and power management ICs. Boost converters are essential in battery-powered systems where the cell voltage sags below the level required by the load, such as converting two NiCd/NiMH cells (approximately 1.8 V to 3.0 V) to a 5 V rail.
Key features include low-power PFM (pulse frequency modulation) control for high efficiency at light loads, an input voltage range extending to 4.5 V, an adjustable output voltage range of approximately 3 V to 5 V, up to 500 mA maximum switch current, and an integrated low battery detect comparator with shutdown mode for power conservation. According to the Fairchild Semiconductor datasheet, the device targets low-voltage DC-DC conversion in 2-cell battery-powered systems.
Technically, the FAN4855 uses asynchronous PFM boost architecture: the internal NPN switch is driven until the current limit or peak threshold is reached, then the inductor energy is released through an external Schottky diode into the output capacitor. PFM operation eliminates the switching-frequency clock of PWM converters, reducing quiescent power and improving efficiency in portable applications.
Typical applications include digital cameras, cell phones, and PDAs, as well as any 2-cell alkaline or NiMH product needing a stable 5 V logic or display rail.
A key design consideration: PFM regulators exhibit variable switching ripple, so output filtering and PCB layout of the inductor and Schottky diode loop require attention for noise-sensitive loads.
This page synthesizes distributor pricing, drop-in alternative data, and practical design notes not found in the manufacturer datasheet.
Bộ thay thế dễ dàng lắp đặt cho FAN4855MTC — cùng gói, chân-to-chân tương thích. Các bộ phận yêu cầu hàn PCB bị loại trừ.
FAN4855MTCX
✅ Drop-In📋 Tham chiếu thay thế (không có trong danh mục)
FAN4855MTCX3
✅ Drop-In📋 Tham chiếu thay thế (không có trong danh mục)
FAN4855MTCX4
✅ Drop-In📋 Tham chiếu thay thế (không có trong danh mục)
FAN4855B
✅ Drop-In📋 Tham chiếu thay thế (không có trong danh mục)
FAN4855MTC Tỷ lệ tối đa & tính chất điện
| Cấu trúc | Boost (step-up) switching regulator |
| Control Scheme | PFM (pulse frequency modulation) |
| Kiểu đầu ra | Positive, Adjustable |
| Khoảng điện áp đầu ra | 3 V to 5 V |
| Số lượng đầu ra | 1 |
| Maximum Switch Current | 500 mA |
| Special Features | Shutdown, Low Battery Detect |
| Hộp | 8-TSSOP (0.173 in, 4.40 mm width) |
| Số lượng chân | 8 |
| Kiểu lắp đặt | Surface Mount |
| Typical Applications | 2-cell battery powered systems (digital cameras, cell phones, PDAs) |
| Efficiency Class | High efficiency (500 mA class) |
| Manufacturer | Fairchild Semiconductor (now onsemi) |
Hướng dẫn cấu hình chân FAN4855MTC 8-tssop (0.173 in, 4.40 mm width)
Cấu hình chân cho FAN4855MTC (8-tssop (0.173 in, 4.40 mm width) gói). Động cơ điện này có chân cổng, nguồn và đầu ra. Đối với các gói không phân極, tham khảo tài liệu thông số kỹ thuật của nhà sản xuất để biết hướng dẫn chính xác của chân 1 và chi tiết về vân footprint. Các ứng dụng phổ biến bao gồm thiết kế nguồn cung cấp điện, điều khiển động cơ và chuyển đổi tải.
Không có dữ liệu chân cụ thể sẵn có cho FAN4855MTC.
Tham khảo: tài liệu kỹ thuật cho cấu hình chân đầy đủ.
Ứng dụng tiêu biểu
FAN4855MTC phù hợp cho 6 Áp dụngs: Digital Camera Power Supply, Cell Phone / PDA Boost Rails, Two-Cell Battery Portable Instruments, 5 V Logic Rail from Low-Voltage Bus, Legacy Board Repair and Sustainment, Low Battery Detection Subsystem.
Digital Camera Power Supply
The FAN4855MTC was designed explicitly for digital cameras powered by two alkaline or NiMH cells, per the Fairchild datasheet general description. Two cells deliver 1.8 V to 3.0 V across discharge, while the LCD backlight, MCU, and flash controller typically require a regulated 5 V rail; the FAN4855MTC boosts this with its 3 V to 5 V adjustable output and 500 mA switch current limit. The integrated low battery detect output warns the camera firmware before the cell voltage collapses, enabling an orderly shutdown and preventing image corruption. Its PFM control keeps efficiency high at the light average loads typical of standby and menu operation. Externally, only an inductor, Schottky diode, and a few capacitors are needed, minimizing BOM cost in consumer hardware.
Được đề xuất
Cell Phone / PDA Boost Rails
Early cell phones and PDAs used two or three cells and needed a stable higher rail for the display, backlight, and logic. The FAN4855MTC addresses this with its low-power PFM boost architecture and 4.5 V maximum input rating, per the Fairchild datasheet. In this role the converter sits between the battery pack and the 5 V system rail, with the shutdown pin allowing the baseband processor to disable the boost during deep sleep, cutting quiescent drain to preserve standby time. The adjustable feedback divider lets the same PCB support 3.3 V or 5 V product variants. Because PFM switching ripple is broadband and load-dependent, designers should budget adequate output capacitance and place the boost loop away from the RF section to protect receiver sensitivity.
Được đề xuất
Two-Cell Battery Portable Instruments
Handheld meters, sensors, and loggers running from two AA or AAA cells benefit from the FAN4855MTC's combination of adjustable output and low battery detect. The feedback network sets any rail from 3 V to 5 V, allowing designers to power 5 V ADCs or 3.3 V microcontrollers directly from declining cell voltage, and the battery-detect comparator can drive an LED or interrupt the MCU when cells approach end of discharge, per the Fairchild datasheet feature set. The 500 mA switch current supports typical measurement front-ends comfortably. With only PFM burst switching at light load, self-consumption stays low enough for months of intermittent-use battery life. Designers should select a low-DCR inductor and a Schottky diode with low forward voltage to preserve efficiency across the full 1.8 V to 3 V input span.
Được đề xuất
5 V Logic Rail from Low-Voltage Bus
Any system with a nominal 3 V to 3.3 V rail that also needs 5 V for legacy peripherals, op-amps, or programming interfaces can use the FAN4855MTC as a local boost stage. With input well within the 4.5 V maximum rating and output adjustable to 5 V, it acts as a point-of-load step-up converter, per distributor and datasheet listings. The shutdown pin allows a host microcontroller to gate the 5 V rail off when unused, reducing idle power. In mixed-voltage boards, the low battery detect input can double as an input-undervoltage lockout by tying it to the input divider, protecting downstream devices from brownout. Keep the inductor switching loop compact and the FB divider close to the IC to maintain regulation accuracy.
Được đề xuất
Legacy Board Repair and Sustainment
Because the FAN4855MTC is discontinued, its most common contemporary role is repairing cameras, phones, and PDAs from the era in which it was designed. Technicians can substitute the pin-identical FAN4855MTCX, FAN4855MTCX3, or FAN4855MTCX4, which IC-Components lists as the comparable cross-reference products, without any board modification; FindIC confirms the identical TSSOP-8, 8-pin, 3 V to 5 V profile. Aftermarket stock from Rochester Electronics (listed on DigiKey), Wolfchip (26,600 pcs as of Jul 15, 2026), and Heisener ($0.76 unit price, 5,440 pcs, as of 2026-09-14) keeps the part procurable for field service. Verify date codes when ordering broker stock for critical repairs.
Được đề xuất
Low Battery Detection Subsystem
Beyond its boost function, the FAN4855MTC integrates a low battery detect comparator, which lets designers implement battery monitoring without a separate supervisory IC, per the Fairchild datasheet title and feature list. The LBD input connects to a resistor divider from the battery; when the cell voltage crosses the programmed threshold, the device flags the system controller. In 2-cell products this supports graceful actions such as dimming the backlight, saving state to memory, or displaying a replace-battery warning before regulation is lost. Combining boost regulation and battery supervision in one 8-TSSOP device reduces BOM count and board area in cost-driven consumer designs, a key reason it was adopted across cameras, cell phones, and PDAs.
Được đề xuất
Tóm tắt các sản phẩm được đề xuất
Dữ liệu tham khảo kỹ thuật cho FAN4855MTC — so sánh, hướng dẫn thiết kế và thông tin tuân thủ.
Hướng dẫn chọn lựa
So sánh với các sản phẩm thay thế
| Tham số | Sản phẩm này | FAN4855MTCX | FAN4855MTCX3 | FAN4855MTCX4 | FAN4855B |
|---|---|---|---|---|---|
| Package | 8-TSSOP (0.173 in, 4.40 mm width) | TSSOP-8 - same | TSSOP-8 - same | TSSOP-8 - same | TSSOP-8 - same |
| Brand | Fairchild Semiconductor (onsemi) | Fairchild Semiconductor (onsemi) | Fairchild Semiconductor (onsemi) | Fairchild Semiconductor (onsemi) | Fairchild Semiconductor (onsemi) |
| Maximum Switch Current | 500 mA | 500 mA | 500 mA | 500 mA | 500 mA (family rating) |
Bảo phân biệt quan trọng
- Integrated low battery detect (vsGeneric PFM boost controllers)
- PFM control for light-load efficiency (vsPWM boost converters)
- Multiple drop-in packaging variants within the family (vsFAN4855MTCX / FAN4855MTCX3 / FAN4855MTCX4)
Ghi chú thiết kế
Keep the boost power loop - input capacitor, inductor, internal switch, Schottky diode, and output capacitor - as compact as possible. PFM burst switching generates broadband ripple, so a short loop minimizes radiated EMI and ground bounce. Place the feedback divider resistors directly adjacent to the FB pin and route the feedback trace away from the inductor and switching node. Use a solid ground plane under the converter area and connect the IC ground pin and capacitor grounds to it with short, wide traces.
The FAN4855 is an asynchronous boost converter: the output diode must be an external Schottky (not a standard-recovery silicon diode), because a slow diode causes large reverse-recovery losses and efficiency collapse at PFM switching rates. Also verify the maximum input voltage of 4.5 V is never exceeded - do not connect three cells or a 5 V USB source directly to the input. Finally, size the inductor saturation current above the 500 mA switch current limit with margin, or regulation will collapse at peak load.
Estimated: at VIN = 2.4 V (2 NiMH cells), VOUT = 5 V and IOUT = 100 mA, input current is roughly VOUT*IOUT/(VIN*efficiency) = 5*100/(2.4*0.8) = 260 mA, well within the 500 mA switch limit, but note input current can approach or exceed the switch limit as battery voltage falls. At end-of-discharge (about 1.8 V), maximum deliverable output current drops substantially; validate load current against the datasheet output-current curves at your minimum expected input voltage before committing to the design.
Thông tin tuân thủ
Compliance status not stated in the provided verified web data; this is an obsolete Fairchild part so consult onsemi product discontinuance notices or Rochester Electronics for RoHS status of available date codes.
