LM8207MTSLASHNOPB datasheet(22/32 Pages) TI1

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LM8207

SNOSAL5A – SEPTEMBER 2005 – REVISED MARCH 2013

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MAXIMUM POWER DISSIPATION

The maximum power dissipation in the LM8207 TSSOP package depends on the ambient temperature and the

increase of the junction temperature of the die. Exceeding the maximum temperature will damage the part. (See

the Absolute Maximum Ratings table.) The VCOM buffer of the LM8207 is designed for use in pulsed conditions.

Driving a continuous current of several hundred mA to a load will damage the part due to the high power

consumption of the output stage of the VCOM buffer.

The maximum operating temperature can be calculated using this formula:

TJ = TA + θJA x PDISSIPATION

where

•

TA = Ambient temperature

•

θJA = Thermal resistance of package (See Operating Ratings table) (84°C/W)

•

PDISSIPATION = Total power dissipation of the LM8207

(4)

Examples:

The estimated power consumption of the LM8207 in a steady state situation with no load is:

VDD

= 16V

IDD

= 6 mA (all buffers within normal operating range)

OUT_VREF

= 14.4V

ILOAD

= 3 mA

VDD x IDD

= 16 V x 6 mA

(VDD - OUT_VREF) x ILOAD = (16 V – 14.4 V) x 3 mA

= 4.8 mW

Total steady state power dissipation

= 100.8 mW

For an ambient temperature TA of 40°C and a dissipated power of 100.8 mW, the junction temperature TJ will be

49°C. This will not exceed the maximum operating temperature.

Two issues are not considered in the calculation:

•

Continuous power dissipation of the gamma buffers. This is load dependent, and can be calculated using the

voltage drop over the output stage times the output current:

–

P = (VDD-VGMAx) x IOUT for current sourcing

–

P = (VGMAx) x IOUT for current sinking

•

Pulsed power dissipation of the buffers. The RMS value of this pulsed current depends on the magnitude of

the current fluctuations and the duty cycle. This can majorly contribute to the total power dissipation.

When the LM8207 is in steady state biasing, the V buffer is considered at three various load conditions:

IOUTRMS (mA)

VCOM Level (V)

Dissipation (mW)

Temp Rise

400

100(1)

800

107

(1)

When IOUTRMS = 100 mA, the package (TJ) will exceed the Operating Temperature

EVALUATION BOARD

For testing purposes an evaluation board is available. It is intended to evaluate the following functions:

•

The Voltage Reference is fully adjustable within the operating range. For optimal output voltage ranges, user

defined resistors can be trimmed by using two resistors in series.

•

The Gamma correction curve is user defined using external resistors. Each optimal value can be achieved by

using two series resistors for fine-tuning.

•

The VCOM node input voltage can be achieved using Texas Instruments’ LM8342 programmable VCOM

calibrator, or using an external supply.

•

For testing, an additional dummy load can be connected to all outputs of the gamma buffers.

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