Datasheet ADM7172 (Analog Devices) - 5

Data Sheet ADM7172 ABSOLUTE MAXIMUM RATINGS Table 4.
The value of θJA may vary, depending on PCB material, layout, and
Parameter Rating
environmental conditions. The specified values of θJA are based VIN to GND −0.3 V to +7 V on a 4-layer, 4 in. × 3 in. circuit board. See JESD51-7 and JESD51-9 for detailed information on the board construction. VOUT to GND −0.3 V to VIN For additional information, see the AN-617 Application Note, EN to GND −0.3 V to +7 V Wafer Level Chip Scale Package. SS to GND −0.3 V to VIN SENSE to GND −0.3 V to +7 V ΨJB is the junction-to-board thermal characterization parameter Storage Temperature Range −65°C to +150°C with units of °C/W. ΨJB of the package is based on modeling and Operating Junction Temperature Range −40°C to +125°C calculation using a 4-layer board. The JESD51-12, Guidelines for Soldering Conditions JEDEC J-STD-020 Reporting and Using Electronic Package Thermal Information, states Stresses at or above those listed under Absolute Maximum that thermal characterization parameters are not the same as Ratings may cause permanent damage to the product. This is a thermal resistances. ΨJB measures the component power flowing stress rating only; functional operation of the product at these through multiple thermal paths rather than a single path as in or any other conditions above those indicated in the operational thermal resistance, θJB. Therefore, ΨJB thermal paths include section of this specification is not implied. Operation beyond convection from the top of the package as wel as radiation from the maximum operating conditions for extended periods may the package, factors that make ΨJB more useful in real-world affect product reliability. applications. Maximum junction temperature (TJ) is calculated from the board temperature (TB) and power dissipation (PD)
THERMAL DATA
using the formula Absolute maximum ratings apply individually only, not in TJ = TB + (PD × ΨJB) combination. The ADM7172 can be damaged when the junction See JESD51-8 and JESD51-12 for more detailed information temperature limits are exceeded. Monitoring ambient temperature about Ψ does not guarantee that T JB. J is within the specified temperature limits. In applications with high power dissipation and poor
THERMAL RESISTANCE
thermal resistance, the maximum ambient temperature may θJA, θJC, and ΨJB are specified for the worst-case conditions, that need to be derated. is, a device soldered in a circuit board for surface-mount In applications with moderate power dissipation and low packages. printed circuit board (PCB) thermal resistance, the maximum
Table 5. Thermal Resistance
ambient temperature can exceed the maximum limit provided that the junction temperature is within specification limits. The
Package Type θJA θJC ΨJB Unit
junction temperature (T 8-Lead LFCSP 36.4 23.5 13.3 °C/W J) of the device is dependent on the ambient temperature (TA), the power dissipation of the device (PD), and the junction-to-ambient thermal resistance of the
ESD CAUTION
package (θJA). Maximum junction temperature (TJ) is calculated from the ambient temperature (TA) and power dissipation (PD) using the formula T J = TA + (PD × θJA) Junction-to-ambient thermal resistance (θJA) of the package is based on modeling and calculation using a 4-layer board. The junction-to-ambient thermal resistance is highly dependent on the application and board layout. In applications where high maximum power dissipation exists, close attention to thermal board design is required. Rev. D | Page 5 of 23 Document Outline FEATURES APPLICATIONS GENERAL DESCRIPTION REVISION HISTORY SPECIFICATIONS INPUT AND OUTPUT CAPACITOR, RECOMMENDED SPECIFICATIONS ABSOLUTE MAXIMUM RATINGS THERMAL DATA THERMAL RESISTANCE ESD CAUTION PIN CONFIGURATION AND FUNCTION DESCRIPTIONS TYPICAL PERFORMANCE CHARACTERISTICS THEORY OF OPERATION APPLICATIONS INFORMATION ADISIMPOWER DESIGN TOOL CAPACITOR SELECTION Output Capacitor Input Bypass Capacitor Input and Output Capacitor Properties PROGRAMMABLE PRECISION ENABLE UNDERVOLTAGE LOCKOUT SOFT START NOISE REDUCTION OF THE ADM7172 IN ADJUSTABLE MODE EFFECT OF NOISE REDUCTION ON START-UP TIME CURRENT-LIMIT AND THERMAL OVERLOAD PROTECTION THERMAL CONSIDERATIONS TYPICAL APPLICATIONS CIRCUITS PRINTED CIRCUIT BOARD LAYOUT CONSIDERATIONS OUTLINE DIMENSIONS ORDERING GUIDE