LT1963A-3.3 — 1.5A Low-Noise Fast Transient Response LDO Regulator

Overview

The LT1963A-3.3 (commonly LT1963EQ-3.3 in TO-263-5 / DDPAK-5 or LT1963EST-3.3 in SOT-223) is a $1.5\text{ A}$ low dropout (LDO) linear regulator manufactured by Analog Devices (originally Linear Technology). Optimized for fast transient response and low output noise ( $40\ \mu\text{Vrms}$ over $10\text{ Hz} \dots 100\text{ kHz}$ ), it provides a clean, stable $+3.3\text{ V}$ DC power rail.

With a low dropout voltage of $340\text{ mV}$ at full $1.5\text{ A}$ load and stability using low-ESR ceramic output capacitors (minimum $10\ \mu\text{F}$ ), the LT1963A-3.3 is widely specified for sensitive RF transceivers, high-resolution ADCs/DACs, FPGA core rails, and high-fidelity audio equipment.

Quick reference


Regulator Type	Low-Noise Fast Transient Response LDO Linear Regulator
Package	TO-263-5 (DDPAK-5) / SOT-223 / TO-220-5 / SOIC-8 EP
Input Voltage Range ( $V_{IN}$ )	$3.8\text{ V}$ to $20.0\text{ V}$ DC
Output Voltage ( $V_{OUT}$ )	$+3.3\text{ V}$ DC (Fixed $\pm 3\%$ precision over temperature)
Max Output Current ( $I_{OUT}$ )	$1.5\text{ A}$ continuous
Dropout Voltage ( $V_{DROP}$ )	$340\text{ mV}$ typical at $I_{OUT} = 1.5\text{A}$
Output Noise Voltage	$40\ \mu\text{Vrms}$ ( $10\text{ Hz}$ to $100\text{ kHz}$ )
Quiescent Supply Current	$1.0\text{ mA}$ typical ( $10\ \mu\text{A}$ in shutdown)

Pinout (TO-263-5 / DDPAK-5 Package)

text

        ┌──────────────────┐
        │   LT1963A-3.3    │  (Top View)
        └─┬──┬──┬──┬──┬────┘
          1  2  3  4  5

Pin	Name	Description
1	`~SHDN~`	Active-LOW Shutdown input pin (Low = Power Down $<10\mu\text{A}$ , High = Enabled)
2	`IN`	Unregulated DC Input power pin (+3.8V to +20.0V DC)
3	`GND`	Ground reference connection (Solder large tab to ground plane)
4	`OUT`	Regulated $+3.3\text{V}$ output pin (Bypass with $\ge 10\mu\text{F}$ capacitor)
5	`SENSE`	Output voltage sense pin (Connect directly to Pin 4 / load rail)

Specifications

Parameter	Symbol	Min	Typ	Max	Unit	Conditions
Input Supply Voltage	$V_{IN}$	3.8	5.0	20.0	V	Operating range for 3.3V output
Output Voltage Precision	$V_{OUT}$	3.23	3.30	3.37	V	$10\text{mA} \le I_{OUT} \le 1.5\text{A}$
Dropout Voltage	$V_{DROP}$	—	340	550	mV	$I_{OUT} = 1.5\text{A}$
Output Noise Voltage	$e_n$	—	40	—	$\mu\text{Vrms}$	$C_{OUT} = 10\mu\text{F}, 10\text{Hz} \dots 100\text{kHz}$
Ripple Rejection (PSRR)	$PSRR$	55	63	—	dB	$f = 120\text{Hz}, V_{IN} = 4.3\text{V} + 0.5\text{Vp-p}$
Shutdown Current	$I_{SHDN}$	—	1.0	10	$\mu\text{A}$	$\overline{SHDN} = 0\text{V}$

Common mistakes

Leaving SENSE pin (Pin 5) unconnected: Pin 5 (SENSE) feeds output voltage back into the internal error amplifier. Leaving Pin 5 floating causes the output to jump to the input rail ( $V_{IN}$ )! Always tie Pin 5 directly to Pin 4 (OUT).
Insufficient PCB copper for thermal dissipation at 1.5A: Dropping 5V down to 3.3V at 1.5A dissipates $P_D = (5\text{V} - 3.3\text{V}) \times 1.5\text{A} = 2.55\text{ W}$ . Solder the TO-263 / SOT-223 tab to a large copper ground plane to prevent thermal shutdown.

Notes

LT1963 vs LT1963A: The "A" revision eliminates reverse current flow back into the input pin when the input is grounded or pulled low, protecting upstream circuitry.