1A Low-Voltage Low-Dropout Regulator
LM39100/39101/39102
Minimum Load Current
The LM39100/1/2 regulator is specified between finite loads.If the output current is too small, leakage currents
dominate and the output voltage rises. A 10mA minimum load current is necessary for proper regulation.
Adjustable Regulator Design
The LM39102 allows programming the output voltage any-where between 1.24V and the 16V maximum operating
rating of the family. Two resistors are used. Resistors can be quite large, up to 1MΩ, because of the very high input
impedance and low bias current of the sense comparator: The resistor values are calculated by : R1=R2(Vout/1.240-
1)
Where VO is the desired output voltage. Figure 1 shows component definition. Applications with widely varying load
currents may scale the resistors to draw the minimum load current required for proper operation (see below).
Power SOP-8 Thermal Characteristics
One of the secrets of the LM39101/2’s performance is its power SO-8 package featuring half the thermal resistance
of a standard SO-8 package. Lower thermal resistance means more output current or higher input voltage for a given
package size.Lower thermal resistance is achieved by joining the four ground leads with the die attach paddle to
create a single-piece electrical and thermal conductor. This concept hasbeen used by MOSFET manufacturers for
years, proving very reliable and cost effective for the user.Thermal resistance consists of two main elements, θ
JC(junction-to-case thermal resistance) and θCA (case-to-ambient thermal resistance). See Figure2. θJC is the
resistance from the die to the leads of the package. θCA is the resistance from the leads to the ambient air and it
includes θCS (case-to-sink thermal resistance) and θSA (sink-to-ambient thermal resistance).Using the power SOP-
8 reduces the θJC dramatically and allows the user to reduce θCA. The total thermal resistance,θJA (junction-to-
ambient thermal resistance) is the limiting factor in calculating the maximum power dissipation capabil-ity of the
device. Typically, the power SOP-8 has a θJC of20°C/W, this is significantly lower than the standard SOP-8 which is
typically 75°C/W. θCA is reduced because pins 5 through 8 can now be soldered directly to a ground plane which
significantly reduces the case-to-sink thermal resis-tance and sink to ambient thermal resistance.Low-dropout linear
regulators from HTC are rated to amaximum junction temperature of 125°C. It is important not to exceed this
maximum junction temperature during operation of the device. To prevent this maximum junction temperature from
being exceeded, the appropriate ground plane heatsink must be used.
Figure3 shows copper area versus power dissipation with each trace corresponding to a different temperature rise
above ambient.From these curves, the minimum area of copper necessary for the part to operate safely can be
determined. The maxi-mum allow able temperature rise must be calculated to deter-mine operation along which
curve.
∆T = TJ(max) – TA(max)
TJ(max) = 125°C
TA(max) = maximum ambient operating temperature
For example, the maximum ambient temperature is 50°C, the∆T is determined as follows:
∆T = 125°C – 50°C
∆T = 75°C
HTC
8
HTC [ HTC KOREA TAEJIN TECHNOLOGY CO. ]
