GUARANTEED 7A PEAK OUTPUT CURRENT GUARANTEED 5A OUTPUT CURRENT ADJUSTABLE OUTPUT DOWN TO 1.2V LINE REGULATION TYPICALLY 0.005%/V LOAD REGULATION TYPICALLY 0.1% GUARANTEED THERMAL REGULATION CURRENT LIMIT CONSTANT WITH TEMPERATURE STANDARD 3-LEAD TRANSISTOR PACKAGE
DESCRIPTION The LM138/LM238/LM338 are adjustable 3-terminal positive voltage regulators capable of supplying in excess of 5A over to 32V output range. They are exceptionally easy to use and require only 2 resistors to set the output voltage. Careful circuit design has resulted in outstanding load and line regulation comparable to many commercial power supplies. The LM138 family is supplied in a standard 3-lead transistor package. A unique feature of the LM138 family is time-de-pendent current limiting. The current limit circuitry allows peak currents to be drawn from the regulator for short periods of time. SCHEMATIC DIAGRAM
This allows the to be used with heavy transient loads and speeds start-up under full-load conditions. Under sustained loading conditions, the current limit decreases to a safe value protecting the regulator. Also included on the chip are thermal overload protection and safe area protection for the power transistor. Overload protection remains functional even if the adjustment pin is accidentally disconnected. Normally, no capacitors are needed unless the device is situated far from the input filter capacitors in which case an input bypass is needed. An optional output capacitor can be added to improve transient response. The adjustment terminal can be bypassed to achieve.very high ripple rejection ratios which are
difficult to achieve with standard 3-terminal regulators. Besides replacing fixed regulators or discrete designs, the LM238 is useful in a wide variety of other applications. Since the regulator is "floating" and sees only the input-to-output differential voltage, supplies of several hundred volts can be ABSOLUTE MAXIMUM RATINGS
Symbol - VO Ptot Tstg Tlead Toper Power Dissipation Storage Temperature Range Lead Temperature (Soldering, 10 seconds) Operating Junction Temperature Range LM238 LM338 Parameter Input Output Voltage Differential Value 35 Internally Limited 125 °C Unit V
regulated as long as the maximum input to input differential is not exceeded. The LM138/LM238/LM338 are packaged in standard steel TO-3 transistor packages. The LM138 is rated for operation from to 150°C, the LM238 from to 150°C and the LM338 from to 125°C.
Absolute Maximum Ratings are those values beyond which damage to the device may occur. Functional operation under these condition is not implied.
Symbol Rthj-case Rthj-amb Parameter Thermal Resistance Junction-case Thermal Resistance Junction-ambient Value 1.4 35 Unit °C/W
ELECTRICAL CHARACTERISTICS OF LM138/LM238 (TJ to 150°C for to 150°C for LM238, VI -VO 2.5 A. Although power dissipation is internally limited, these specifications apply to power dissipation to 50W, unless otherwise specified).
Symbol KVI KVO Parameter Line Regulation (Note 1) Load Regulation (Note 1) Thermal Regulation Adjustment Pin Current Adjustment Pin Current Change Reference Voltage Line Regulation (Note 1) Load Regulation (Note 1) Temperature Stability Minimum Load Current Limit = 25°C, Test Conditions 5 A Pulse V 1.19 Min. Typ. 0.5 ms Peak 30 V Max. Unit %/V mV % %/W µA V %/V mA A
RMS Output Noise of VO) Ripple Rejection Ratio Long Term Stability
Note 1: Regulation is measured at constant junction temperature. Changes in output voltage due to heating effects are taken into account separately by thermal rejection.