LM2596DSADJR4G

The LM2596DSADJR4G from onsemi is an adjustable output version of the LM2596 SIMPLE SWITCHER step-down voltage regulator family, designed to provide a regulated output voltage from 1.23V to 37V at up to 3A load current from an input voltage range of 4.5V to 40V. The DSADJ suffix denotes: D for D2PAK (TO-263-5) surface-mount package, ADJ for adjustable output, and R4G for onsemi’s RoHS-compliant, lead-free packaging. The output voltage is set by an external resistor divider connected to the feedback pin, with the internal reference voltage of 1.23V determining the minimum output voltage. The 150kHz fixed switching frequency allows the use of smaller inductors and capacitors compared to lower-frequency designs, while still enabling efficient operation at high step-down ratios. The device requires only four external components (input capacitor, output capacitor, catch diode, and inductor) plus the feedback divider for a complete step-down regulator solution. Internal frequency compensation eliminates the need for external compensation components. The TTL-compatible shutdown pin reduces quiescent current to 80uA for standby operation. Protection features include cycle-by-cycle current limiting through a two-stage frequency foldback scheme and thermal shutdown. The D2PAK package provides excellent thermal performance with a junction-to-case thermal resistance that supports the full 3A output current with appropriate PCB copper area for heat sinking.

The LM2596DSADJR4G operates as a fixed-frequency buck (step-down) switching regulator with adjustable output. Key subsystems include: (1) Internal Oscillator – a 150kHz fixed-frequency oscillator sets the switching period; this frequency balances efficiency and component size; (2) Current-Mode PWM – the output switch is controlled by a pulse-width modulator that compares the error amplifier output with the switch current; current-mode control provides inherent current limiting and simplified loop compensation; (3) Power Switch – an integrated NPN Darlington power switch rated for 40V and 3A; the switch saturation voltage is typically 1.5V at 3A, contributing to conduction losses; (4) Error Amplifier and Reference – a precision 1.23V bandgap reference is compared with the divided-down output voltage at the FB pin; the error amplifier drives the PWM modulator to maintain the output at the setpoint; output voltage is calculated as VOUT = 1.23V x (1 + R1/R2) where R1 connects from VOUT to FB and R2 connects from FB to ground; (5) Shutdown Control – when the ON/OFF pin is driven above 1.4V, the device enters shutdown mode with 80uA quiescent current; grounding the pin enables normal operation; (6) Protection – two-stage current limiting: first stage limits switch current to approximately 4.5A; if overload persists, switching frequency is reduced from 150kHz to approximately 50kHz (frequency foldback) to protect the catch diode and reduce power dissipation; thermal shutdown activates at approximately 155C junction temperature.

• Adjustable lab supply: 24V input to 1.23-20V adjustable output with potentiometer divider
• Battery charger: 12V-24V input to 8.4V (2-cell Li-Ion) or 12.6V (3-cell) charger output
• Industrial 24V to 5V/3.3V: D2PAK package handles 3A for multiple logic loads from 24V field supply
• Automotive accessory: 12V battery to variable output for LED brightness control