LT1129IQ - 700mA Micropower LDO Regulator with Shutdown | ADI
MPN： LT1129IQ ✓ 啟用中LT1129IQ 概覽
An LDO (Low-Dropout) linear regulator is a type of voltage regulator that maintains a stable output voltage even when the input voltage approaches the output voltage, with dropout voltage being the minimum VIN-VOUT differential required to maintain regulation. LDOs sit within the broader hierarchy of linear regulators, which in turn are part of the power management IC family of semiconductors. They are preferred over switching regulators in noise-sensitive applications because they introduce no switching ripple.
Key features include 0.4 V dropout voltage at full 700 mA load, 50 µA quiescent current during normal operation, 16 µA quiescent current in shutdown mode, and the absence of required protection diodes. The device is stable with only 3.3 µF of output capacitance, significantly less than older regulators that require 10–100 µF, simplifying board design and reducing BOM cost.
The LT1129IQ uses a PNP pass transistor architecture that achieves low dropout while maintaining controlled quiescent current in dropout conditions. Reverse-battery protection is built in: the input may be connected to ground or a reverse voltage without reverse current flow from output to input, a critical feature for automotive and battery applications.
Typical applications include battery-powered portable instruments, post-regulators for switching supplies, automotive electronics, point-of-load regulation, and handheld instrumentation requiring long battery life. The wide 30 V input range also makes it suitable for industrial 24 V bus systems.
When designing with this part, pay attention to thermal management. At VIN = 24 V, VOUT = 5 V, and 700 mA load, the LT1129IQ dissipates approximately 13.3 W. The DDPAK-5 package requires substantial copper area or a heatsink to keep junction temperature within the 125 °C operating limit.
This page synthesizes distributor pricing, drop-in alternatives, and practical design notes not found in the manufacturer datasheet.
直接替換替代品，適用於 LT1129IQ — 相同封裝，腳位對腳位相容。需重新設計 PCB 的不同封裝零件不列入。
此系列的變體
與下列產品可直接替換的同系列型號： LT1129IQ （相同外形與佔位） — 差異在於 Dropout Voltage, Input Voltage Range, Maximum Output Current, Operating Temperature Range, Output Voltage Range.
LT1129IQ#PBF
✅ 直接替換📋 參考替代品（不在目錄中）
LT1129IST#PBF
✅ 直接替換📋 參考替代品（不在目錄中）
LT1129IQ-5#PBF
✅ 直接替換📋 參考替代品（不在目錄中）
LP38691SD-ADJ/NOPB
✅ 直接替換聯絡詢價
查看資料表 →TPS7A4501DDC
✅ 直接替換📋 參考替代品（不在目錄中）
LT1129IQ 最大額定值與電氣特性
| 拓撲 | LDO Linear Regulator |
| 輸出類型 | Adjustable |
| 輸出電壓範圍 | 3.8 V to 30 V (adjustable) |
| 輸入電壓範圍 | 4.5 V to 30 V |
| 最大輸出電流 | 700 mA |
| 壓降電壓 | 0.4 V at 700 mA |
| Quiescent Current (Operating) | 50 µA |
| Quiescent Current (Shutdown) | 16 µA |
| Output Capacitor for Stability | 3.3 µF minimum |
| 工作溫度範圍 | -40 °C to +125 °C |
| 封裝 | DDPAK-5 (TO-263-5) |
| 安裝類型 | Surface Mount |
| Protection Features | Current limit, thermal shutdown, reverse-battery protection |
| Shutdown Pin | Yes (active-high) |
| Reverse Current Protection | Built-in (no input protection diodes required) |
| RoHS 狀態 | Compliant (lead-free #PBF suffix) |
LT1129IQ 腳位配置
| 腳位 1 | ADJ — Adjustable feedback input (connect to VOUT via resistor divider) |
| 腳位 2 | SHDN — Shutdown pin (active-high; tie to VIN if unused) |
| 腳位 3 | GND — Ground |
| 腳位 4 | VIN — Input supply voltage (4.5 V to 30 V) |
| 腳位 5 | VOUT — Regulated output voltage |
| 腳位 TAB | GND — Exposed thermal pad - must be soldered to PCB ground plane for thermal dissipation |
典型應用
LT1129IQ 適用於 6 應用s: Battery-Powered Portable Instruments, Post-Regulator for Switching Supplies, Automotive Electronics - 12V/24V Bus, Point-of-Load (POL) Regulation, Industrial 24V Bus Systems, Handheld Test & Measurement Equipment.
Battery-Powered Portable Instruments
The LT1129IQ's 50 µA quiescent current and 16 µA shutdown current make it ideal for battery-powered portable instruments where extending battery life is critical. Placed between a 9 V or 12 V battery stack and the analog/digital rails, it delivers 700 mA with only 0.4 V dropout, ensuring efficient regulation even as the battery discharges. Unlike switching regulators, the LDO architecture introduces no switching noise into sensitive measurement circuits. A 3.3 µF ceramic output capacitor is sufficient for stability, reducing BOM cost and board space compared to legacy 10–100 µF designs.
推薦
Post-Regulator for Switching Supplies
The LT1129IQ serves as an excellent post-regulator after a switching converter to eliminate ripple and provide a clean DC rail for noise-sensitive analog circuits. With 0.4 V dropout at 700 mA, it can be placed downstream of a 5 V or 12 V switching regulator with minimal headroom penalty. The wide 30 V input range handles upstream switching converter outputs from various topologies including buck and SEPIC. Compared to the TPS7A4501DDC, the LT1129IQ's 50 µA quiescent current is significantly lower, making it better for sleep-mode designs in industrial and IoT systems.
推薦
Automotive Electronics - 12V/24V Bus
The LT1129IQ's reverse-battery protection, 30 V input range, and 700 mA output make it well-suited for 12V and 24V automotive electronics including body control modules, infotainment peripherals, and sensor conditioning. According to the ADI datasheet 112935ff, the device tolerates input reversal without damage, a critical feature when jump-starting or connecting a reversed battery. The shutdown pin enables ECU-controlled power management, while the DDPAK-5 package provides the thermal performance needed for under-hood and cabin-mounted applications. The fixed -5V variant suits analog sensor rails.
推薦
Point-of-Load (POL) Regulation
For distributed point-of-load applications on densely populated PCBs, the LT1129IQ's DDPAK-5 footprint and 700 mA capability allow placement near high-current digital loads such as FPGAs, microprocessors, and memory banks. The 50 µA quiescent current keeps standby power low when the load is disabled via the SHDN pin. Compared to the LT1963A in TO-220, the LT1129IQ saves significant PCB area while delivering comparable performance. The device's thermal performance requires careful copper pour design but is manageable in standard 4-layer boards.
推薦
Industrial 24V Bus Systems
Industrial automation and control systems using 24V bus architectures benefit from the LT1129IQ's 30 V input range, 700 mA output, and reverse-input protection. It can power sensor interfaces, RS-485 transceivers, PLC I/O modules, and HMI displays directly from the 24V rail with minimal dissipation. The micropower quiescent current suits battery-backed industrial controllers that must operate during power interruptions. According to the ADI datasheet, the device is stable with 3.3 µF output capacitance, enabling compact designs in space-constrained industrial enclosures.
推薦
Handheld Test & Measurement Equipment
Handheld multimeters, oscilloscopes, and field test instruments rely on the LT1129IQ to extend battery runtime while delivering clean power to analog front ends and ADC reference circuits. The 50 µA quiescent current preserves battery life when the instrument is in standby, while 700 mA peak current supports backlight LED drivers and active measurement loads. The DDPAK-5 surface-mount package enables compact handheld form factors. Compared to the LP38691SD-ADJ, the LT1129IQ provides 40% more output current (700 mA vs 500 mA), useful for driving LED bargraph displays and piezo buzzer drivers.
推薦
推薦產品摘要
工程參考資料，適用於 LT1129IQ — 比較、設計指引及合規資訊。
選型指南
與替代品比較
| 參數 | 本產品 | LT1129IQ#PBF | LT1129IST#PBF | LT1129IQ-5#PBF | LP38691SD-ADJ/NOPB | TPS7A4501DDC |
|---|---|---|---|---|---|---|
| Brand | Analog Devices | Analog Devices | Analog Devices | Analog Devices | Texas Instruments | Texas Instruments |
| Package | DDPAK-5 | DDPAK-5 - same | DDPAK-5 - same | DDPAK-5 - same | DDPAK-5 (TO-263-5) - same | DDPAK-5 - same |
| Output Current | 700 mA | 700 mA | 700 mA | 700 mA | 500 mA (-29%) | 500 mA (-29%) |
| Dropout Voltage | 0.4 V at 700 mA | 0.4 V | 0.4 V | 0.4 V | 0.25 V (better) | 0.2 V (better) |
| Quiescent Current | 50 µA | 50 µA | 50 µA | 50 µA | 100 µA (worse) | 1.2 mA (worse) |
| Shutdown Pin | Yes (active-high) | Yes | Yes | Yes | Yes | Yes |
| Input Voltage Range | 4.5 V to 30 V | 4.5 V to 30 V | 4.5 V to 30 V | 4.5 V to 30 V | 2.7 V to 10 V (narrower) | 1.9 V to 20 V (narrower) |
| Reverse Battery Protection | Yes (built-in) | Yes | Yes | Yes | No (external diode required) | No |
主要差異化特點
- Lowest quiescent current in DDPAK-5 LDO class (對比TPS7A4501DDC)
- Highest output current in micropower DDPAK-5 LDO class (對比LP38691SD-ADJ/NOPB)
- Built-in reverse-battery protection (對比LP38691SD-ADJ/NOPB)
- Widest input voltage range with shutdown in DDPAK-5 class (對比LP38691SD-ADJ/NOPB)
設計說明
At VIN = 24 V, VOUT = 5 V, and 700 mA load, the LT1129IQ dissipates approximately 13.3 W of power (estimated: (VIN-VOUT) × IOUT = 19 V × 0.7 A). The DDPAK-5 package has a junction-to-ambient thermal resistance of approximately 30 °C/W on a standard JEDEC EIA/JESD51 4-layer test board, resulting in a junction temperature rise of ~400 °C above ambient. A heatsink or at least 1 square inch of PCB copper pour is mandatory for reliable operation at full load with high input-to-output differentials. Always verify thermal performance in your specific PCB layout.
Place input and output capacitors as close to the IC pins as possible using short, wide traces. Use a 3.3 µF or larger low-ESR ceramic capacitor on the output (tantalum or aluminum polymer also acceptable). Add a 1 µF ceramic bypass capacitor on the input if the source impedance is high or the input trace is long. The exposed thermal pad (TAB) MUST be soldered to a PCB ground plane with thermal vias to dissipate heat - this is the primary heatsinking path for the DDPAK-5 package.
Do not omit the output capacitor - the LT1129IQ requires a minimum of 3.3 µF for stability and will oscillate if the output capacitance is insufficient or has too high ESR. When using the adjustable version, ensure the feedback resistor divider uses 1% or better tolerance resistors to maintain output voltage accuracy. The SHDN pin must not be left floating - tie it to VIN if shutdown functionality is not used, otherwise the regulator may enter an undefined state. Avoid exceeding the absolute maximum VIN of 30 V during transient conditions such as load dumps in automotive systems.
Route the feedback trace (pin 1 ADJ) away from noisy switching nodes and minimize its length to avoid picking up noise that couples into the output voltage. Use a ground plane directly under the regulator to provide low-impedance return paths. For adjustable versions, place the resistor divider close to the ADJ pin with the ground-side resistor connected directly to the ground plane, not to the load ground - this prevents load-current-induced ground drops from corrupting the output voltage regulation.
The LT1129IQ's 50 µA quiescent current is constant regardless of load, making it efficient at light loads but proportionally larger as a percentage of total power at very light loads (e.g., <1 mA). For ultra-light-load battery applications below 100 µA, consider an LDO with sub-µA quiescent current or a nanopower buck converter. The 16 µA shutdown current allows further power reduction when the load can be disabled via the SHDN pin. The reverse-battery protection eliminates the need for an external series protection diode, saving BOM cost and forward-voltage drop.
合規資訊
RoHS compliance applies to #PBF suffix variants. Standard LT1129IQ (non-PBF) may not be RoHS compliant. AEC-Q100 qualification status not explicitly stated in the verified data - confirm with ADI for automotive applications. The -Q suffix variants may exist for automotive-grade qualification.
