LT1185CQ - 3A Low Dropout Regulator, Adjustable, DDPAK-5 | Analog Devices
N.º da peça: LT1185CQ ✓ AtivoLT1185CQ Visão geral
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. LDOs sit within the broader hierarchy: LDO -> linear regulator -> voltage regulator -> power management IC -> semiconductor. The LT1185 belongs to the NPN-pass-transistor family, where a saturation-limited NPN device is used as the pass element - this trades efficiency for very low dropout voltage compared to PNP designs.
Key specifications include 3A continuous output current, 0.25 ohm on-resistance of the internal pass transistor, 2.5mA typical quiescent current, programmable current limit, and full remote sense capability for accurate regulation at the load. The device also offers a shutdown pin for power sequencing, internal 1.25V reference, and good high-frequency ripple rejection. The DDPAK-5 (TO-263 style) package with tab provides low thermal resistance for high-current dissipation.
The LT1185 uses a bipolar architecture with the saturation-limited NPN pass transistor. This topology yields very low dropout (input-to-output differential) while providing robust current-limit behavior. The reference is trimmed to ±1%, and the current-limit comparator can be programmed with a single external resistor, allowing the designer to optimize protection for the load and the pass transistor under fault conditions.
Typical applications include post-regulation for switching converters (where the LDO cleans up switching ripple), industrial 24V-bus regulation, high-current instrumentation supplies, and negative-rail regulation in telecom systems. The wide input range supports automotive and industrial transients, while the remote-sense pins eliminate IR drops in long PCB traces.
When designing with the LT1185, account for the 2.5mA quiescent current that flows even at no-load - this impacts battery-powered applications. The remote-sense pins must be tied directly to the load for best accuracy; do not leave them disconnected.
This page synthesizes distributor pricing, drop-in alternatives, and practical design notes not found in the manufacturer datasheet alone.
Alternativas drop-in para LT1185CQ — mesmo encapsulamento, compatível pino a pino. Peças de encapsulamento diferente que exigem retrabalho na PCB são excluídas.
LT1185IQ#PBF
✅ Drop-In📋 Alternativa de referência (fora do catálogo)
LT1185CQ#PBF
✅ Drop-In📋 Alternativa de referência (fora do catálogo)
LT1185CQ#TRPBF
✅ Drop-In📋 Alternativa de referência (fora do catálogo)
LT1185CQ Classificações máximas e características elétricas
| Manufacturer | Analog Devices (formerly Linear Technology) |
| Part Number | LT1185CQ |
| Regulator Type | LDO, Positive or Negative Adjustable |
| Número de saídas | 1 |
| Faixa de tensão de saída | 2.5 V to 25 V |
| Corrente máxima de saída | 3 A |
| Reference Voltage Accuracy | ±1% |
| Pass Transistor On-Resistance | 0.25 ohm |
| Corrente de repouso | 2.5 mA (typical) |
| Limitação de corrente | Adjustable / Programmable |
| Remote Sense | Yes (full remote sense) |
| Shutdown Pin | Yes |
| Encapsulamento / Caixa | DDPAK-5 (TO-263-5) |
| Tipo de montagem | Surface Mount |
| Status RoHS | Compliant (PBF suffix) |
| Topologia | Saturation-limited NPN pass transistor |
Configuração de pinos do LT1185CQ
| Pino 1 | ADJ/SENSE — Adjustable feedback input / remote sense (tie to load for remote-sense operation) |
| Pino 2 | SHDN — Shutdown (active high; tie high for normal operation) |
| Pino 3 | GND — Ground |
| Pino 4 | VIN — Input supply voltage |
| Pino 5 | VOUT — Regulated output voltage |
Aplicações típicas
LT1185CQ é adequado para 6 aplicaçãos: Post-Regulation for Switching Converters, Industrial 24V Bus Regulation, High-Current Instrumentation Power Supply, Telecom Negative-Rail Generation, Automotive 12V Accessory Power, FPGA Core and I/O Rail Post-Regulation.
Post-Regulation for Switching Converters
The LT1185CQ sits downstream of a switching buck or boost stage to clean up switching ripple, delivering clean 2.5V-25V rails at up to 3A. With its 0.25 ohm NPN pass transistor and full remote sense, it eliminates the last 10-30 mV of ripple from a 5V/3.3V switcher while keeping dropout under 0.75V at full load. Placed between the switcher's output and the load with a 10uF input cap and 10uF output cap, it adds no switching noise of its own but dissipates extra power at large VIN-VOUT deltas - estimate 1.5W at 5V to 3.3V at 1A.
Recomendado
Industrial 24V Bus Regulation
Factory automation backplanes often run a noisy 24V bus that must be regulated down to 5V, 12V or 15V for PLC and sensor power. The LT1185CQ handles input transients common on industrial buses and outputs a regulated 2.5V-25V rail at 3A with ±1% accuracy. Its full remote-sense pins compensate for IR drop across long PCB traces or terminal-block wiring - critical when the regulator sits far from the actual load. Use a 22uF or larger input capacitor to survive industrial surge events.
Recomendado
High-Current Instrumentation Power Supply
Bench-top and ATE instrumentation needs quiet, accurate rails at multi-amp currents - exactly what the LT1185CQ's ±1% reference and full remote-sense architecture deliver. The regulator supplies 3A to analog signal chains, ADC/DAC reference buffers, or precision op-amp rails without the switching noise of a buck converter. The 2.5mA quiescent current is acceptable for line-powered instruments where efficiency matters less than output accuracy. The shutdown pin enables hardware-controlled standby.
Recomendado
Telecom Negative-Rail Generation
Telecom systems often need -5V, -12V or -15V rails alongside positive supplies. The LT1185CQ's unique dual-mode topology lets it operate as a standard negative regulator with grounded input, delivering up to -3A at output voltages as low as -2.5V. This eliminates a separate negative LDO on the BOM. The same DDPAK-5 footprint and pinout are used for both modes - only external resistor and capacitor connections change. Source: Analog Devices LT1185 datasheet application diagrams.
Recomendado
Automotive 12V Accessory Power
The LT1185CQ regulates the noisy 12V automotive accessory rail down to a clean 5V or 8V for infotainment, telematics, and sensor electronics. With a saturation-limited NPN pass transistor, it tolerates load-dump transients better than many CMOS LDOs, and 3A output supports multiple downstream loads from one regulator. Programmable current limit protects wiring harnesses during fault conditions. Note: automotive qualification (AEC-Q100) status is not confirmed in the public datasheet - verify before automotive deployment.
Recomendado
FPGA Core and I/O Rail Post-Regulation
FPGAs and high-performance processors need clean, low-noise core and I/O rails with tight accuracy. The LT1185CQ post-regulates a switching converter's output to supply 1.0V-3.3V rails (after divider scaling) at up to 3A with ±1% accuracy, with full remote sense eliminating PCB-trace IR drops to the die. The shutdown pin supports power-sequencing requirements of FPGA rails. The exposed tab of the DDPAK-5 package allows direct heatsinking for sustained 3A loads in dense layouts.
Recomendado
Resumo dos produtos recomendados
Dados de referência de engenharia para LT1185CQ — comparação, orientação de projeto e informações de conformidade.
Guia de seleção
Comparação com alternativas
| Parâmetro | Este produto | LT1185IQ#PBF | LT1185CQ#PBF | LT1185CQ#TRPBF | LT1185CT#PBF |
|---|---|---|---|---|---|
| Package | DDPAK-5 (TO-263-5) | DDPAK-5 (TO-263-5) - same | DDPAK-5 (TO-263-5) - same | DDPAK-5 (TO-263-5) - same | TO-220-5 - through-hole, different footprint |
| Brand | Analog Devices | Analog Devices | Analog Devices | Analog Devices | Analog Devices |
| Output Current | 3 A | 3 A | 3 A | 3 A | 3 A |
| Output Voltage Range | 2.5V to 25V | 2.5V to 25V | 2.5V to 25V | 2.5V to 25V | 2.5V to 25V |
| Operating Temperature Range | 0C to +70C (commercial) | -40C to +125C (industrial) | 0C to +70C (commercial) | 0C to +70C (commercial) | 0C to +70C (commercial) |
| Reference Accuracy | ±1% | ±1% | ±1% | ±1% | ±1% |
| Shutdown Capability | Yes | Yes | Yes | Yes | Yes |
| Lead-Free / RoHS | RoHS compliant (PBF) | RoHS compliant | RoHS compliant | RoHS compliant | RoHS compliant |
| Packaging Format | Tube (Q suffix) | Tube | Tube | Tape & Reel | Tube (TO-220) |
Principais diferenciais
- Dual positive/negative output configuration from one part (vs LM350T)
- Full remote sense for accurate load regulation (vs LT1083CP)
- Programmable current limit protects pass transistor and load (vs LT1185CT#PBF (TO-220))
Notas de projeto
Estimated: at 3A load with VIN=8V and VOUT=5V, the LT1185CQ dissipates 9W. With the DDPAK-5 thermal tab soldered to roughly 1 sq inch of 2 oz copper on a standard FR-4 board, theta_JA is approximately 30-40 C/W, producing a 270-360 C junction temperature rise. An external heatsink or substantially larger copper area is required for continuous 3A operation above ~1.5W dissipation. Always check junction temperature in the worst-case VIN/IOUT/TA corner.
Place input and output capacitors as close as possible to the LT1185CQ pins to minimize parasitic inductance. Use a low-ESR 10uF or larger input capacitor to handle the saturation-limited NPN pass transistor's switching transients. Connect the remote-sense pin (ADJ/SENSE, pin 1) directly at the load - do not tie it at the regulator output, or PCB-trace resistance will degrade regulation accuracy.
Do not leave the SHDN pin floating - tie it to VIN through a 100k resistor or drive it actively; a floating SHDN pin can result in unpredictable on/off state. The current-limit programming resistor must be sized for the worst-case load plus startup inrush. Verify the LT1185CQ's absolute maximum input voltage (typically 35V) against your upstream rail under transient conditions including load-dump and inductive kickback.
Informações de conformidade
LT1185CQ#PBF suffix indicates Pb-free/RoHS compliant finish per Analog Devices ordering information. AEC-Q100 automotive grade is not stated in public datasheet - verify with ADI for automotive deployment. Halogen-free status not confirmed in verified web data.
