Datasheet LT1176, LT1176-5 (Analog Devices) - 4

LT1176/LT1176-5
ELECTRICAL CHARACTERISTICS The
l
denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. TJ = 25°C, VIN 25V, unless otherwise noted. PARAMETER CONDITIONS MIN TYP MAX UNITS
Status Low Level ISTATUS = 1.6mA Sinking l 0.25 0.4 V Status Delay Time 9 µs Status Minimum Width 30 µs
Note 1:
Stresses beyond those listed under Absolute Maximum Ratings
Note 5:
Switch frequency is internally scaled down when the feedback pin may cause permanent damage to the device. Exposure to any Absolute voltage is less than 1.3V to avoid extremely short switch-on times. During Maximum Rating condition for extended periods may affect device testing, VFB or VSENSE is adjusted to give a minimum switch-on time of reliability and lifetime. 1µs.
Note 2:
To calculate maximum switch ON voltage at current between low
Note 6:
ILM = (RLIM – 1k)/7.65k and high conditions, a linear interpolation may be used.
Note 7:
Switch to input voltage limitation must also be observed.
Note 3:
A feedback pin voltage (VFB) of 2.5V forces the VC pin to its low
Note 8:
VMAX = 35V clamp level and the switch duty cycle to zero. This approximates the
Note 9:
Does not include switch leakage. zero load condition where duty cycle approaches zero. The LT1176-5 has V
Note 10:
Error amplifier voltage gain and transconductance are SENSE = 5.5V. specified relative to the internal feedback node. To calculate gain and
Note 4:
Total voltage from VIN pin to ground pin must be ≥ 8V after transconductance from the sense pin (Output) to the V start-up for proper regulation. C pin on the LT1176-5, multiply by 0.44.
Application Hints
Although the LT1176 has a peak switch rating of 1.2A and a maximum duty Power = ILOAD(VOUT/VIN) + VIN [7mA + 3mA (VOUT/VIN) + 0.012 (ILOAD)] cycle of 85%, it must be used cautiously in applications which require high IPEAK = ILOAD(PEAK) + [VOUT(VIN – VOUT)]/2E5(VIN)(L) switch current and high duty cycle simultaneously, to avoid excessive chip Example: V temperature. Thermal resistance is 90°C/W for the 8-pin DIP package and IN = 15V, VOUT = 5V, ILOAD = 0.5A Continuous, 0.8A Peak, L = 100µH 50°C/W for the 20-pin SO. This limits continuous chip power dissipation to the 0.5W to 1W range. These numbers assume typical mounting techniques. Power (ILOAD = 0.5A) = 0.38W Extra or thick copper connected to the leads can reduce thermal resistance. IPEAK (ILOAD = 0.8A) = 0.97A Bonding the package to the board or using a clip style heat sink can also help. Where component size or height is critical, we suggest using solid tantalum The following formulas will give chip power dissipation and peak switch current capacitors (singly or in parallel), but be sure to use units rated for switching for the standard buck converter. Note that surges less than 30 seconds do not applications. Coiltronics is a good source for low profile surface mount need to be considered from a thermal standpoint, but for proper regulation, inductors and AVX makes high quality surface mount tantalum capacitors. For they must not result in peak switch currents exceeding the 1.2A limit. further help, use Application Notes 19 and 44,LTC’s SwitcherCAD® computer design program, and our knowledgeable application department. 11765fb 4 Document Outline Features Applications Description Typical Application Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Block Diagram Package Description Revision History Package Description