LT1129IQ - 700mA Micropower LDO Regulator with Shutdown | ADI
Référence : LT1129IQ ✓ ActifLT1129IQ Présentation
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.
Alternatives de remplacement direct pour LT1129IQ — même boîtier, compatible broche à broche. Les références à boîtier différent nécessitant une retouche du PCB sont exclues.
Variantes de cette série
Modèles de la même série directement compatibles avec LT1129IQ (même facteur de forme et même empreinte) — différant par Dropout Voltage, Input Voltage Range, Maximum Output Current, Operating Temperature Range, Output Voltage Range.
LT1129IQ#PBF
✅ Remplacement direct📋 Alternative de référence (hors catalogue)
LT1129IST#PBF
✅ Remplacement direct📋 Alternative de référence (hors catalogue)
LT1129IQ-5#PBF
✅ Remplacement direct📋 Alternative de référence (hors catalogue)
LP38691SD-ADJ/NOPB
✅ Remplacement directContactez-nous pour le prix
Voir la fiche technique →TPS7A4501DDC
✅ Remplacement direct📋 Alternative de référence (hors catalogue)
LT1129IQ Valeurs maximales et caractéristiques électriques
| Topologie | LDO Linear Regulator |
| Type de sortie | Adjustable |
| Plage de tension de sortie | 3.8 V to 30 V (adjustable) |
| Plage de tension d'entrée | 4.5 V to 30 V |
| Courant de sortie maximal | 700 mA |
| Tension de déchet | 0.4 V at 700 mA |
| Quiescent Current (Operating) | 50 µA |
| Quiescent Current (Shutdown) | 16 µA |
| Output Capacitor for Stability | 3.3 µF minimum |
| Plage de température de fonctionnement | -40 °C to +125 °C |
| Boîtier | DDPAK-5 (TO-263-5) |
| Type de montage | 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) |
| Statut RoHS | Compliant (lead-free #PBF suffix) |
Configuration des broches de LT1129IQ
| Broche 1 | ADJ — Adjustable feedback input (connect to VOUT via resistor divider) |
| Broche 2 | SHDN — Shutdown pin (active-high; tie to VIN if unused) |
| Broche 3 | GND — Ground |
| Broche 4 | VIN — Input supply voltage (4.5 V to 30 V) |
| Broche 5 | VOUT — Regulated output voltage |
| Broche TAB | GND — Exposed thermal pad - must be soldered to PCB ground plane for thermal dissipation |
Applications typiques
LT1129IQ convient pour 6 applications: 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.
Recommandé
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.
Recommandé
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.
Recommandé
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.
Recommandé
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.
Recommandé
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.
Recommandé
Récapitulatif des produits recommandés
Données de référence d'ingénierie pour LT1129IQ — comparaison, recommandations de conception et informations de conformité.
Guide de sélection
Comparaison avec les alternatives
| Paramètre | Ce produit | 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 |
Principaux différenciateurs
- Lowest quiescent current in DDPAK-5 LDO class (vs TPS7A4501DDC)
- Highest output current in micropower DDPAK-5 LDO class (vs LP38691SD-ADJ/NOPB)
- Built-in reverse-battery protection (vs LP38691SD-ADJ/NOPB)
- Widest input voltage range with shutdown in DDPAK-5 class (vs LP38691SD-ADJ/NOPB)
Notes de conception
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.
Informations de conformité
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.
