EL5325AIRZ-T7 데이터 시트보기 (PDF) - Renesas Electronics

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EL5325AIRZ-T7

12-Channel TFT-LCD Reference Voltage Generator with External Shutdown

Renesas Electronics 

EL5325A

is on external clock mode. Setting B14 to low, the chip is on

internal clock mode.

CHANNEL OUTPUTS

Each of the channel outputs has a rail-to-rail buffer. This

enables all channels to have the capability to drive to within

50mV of the power rails, (see Electrical Characteristics for

details).

When driving large capacitive loads, a series resistor should be

placed in series with the output. (Usually between 5 and

50).

Each of the channels is updated on a continuous cycle, the

time for the new data to appear at a specific output will depend

on the exact timing relationship of the incoming data to this

cycle.

The best-case scenario is when the data has just been captured

and then passed on to the output stage immediately; this can be

as short as 48µs. In the worst-case scenario this will be 576µs

when the data has just missed the cycle.

When a large change in output voltage is required, the change will

occur in 2V steps, thus the requisite number of timing cycles will

be added to the overall update time. This means that a large

change of 16V can take between 4.6ms to 5.2ms depending on

the absolute timing relative to the update cycle.

POWER DISSIPATION AND THERMAL SHUTDOWN

With the 30mA maximum continues output drive capability for

each channel, it is possible to exceed the 125°C absolute

maximum junction temperature. Therefore, it is important to

calculate the maximum junction temperature for the application

to determine if load conditions need to be modified for the part

to remain in the safe operation.

The maximum power dissipation allowed in a package is

determined according to:

PDMAX

=

T----J---M-----A----X-----------T----A----M----A----X--

JA

where:

• TJMAX = Maximum junction temperature

• TAMAX = Maximum ambient temperature

• JA = Thermal resistance of the package

• PDMAX = Maximum power dissipation in the package

The maximum power dissipation actually produced by the IC is

the total quiescent supply current times the total power supply

voltage and plus the power in the IC due to the loads.

PDMAX = VS  IS + VS - VOUTi   ILOADi

when sourcing, and:

PDMAX = VS  IS + VOUTi  ILOADi

when sinking.

Where:

• i = 1 to total 12

• VS = Supply voltage

• IS = Quiescent current

• VOUTi = Output voltage of the i channel

• ILOADi = Load current of the i channel

By setting the two PDMAX equations equal to each other, we

can solve for the RLOADs to avoid the device overheat. The

package power dissipation curves provide a convenient way to

see if the device will overheat.

The EL5325A has an internal thermal shutdown circuitry that

prevents overheating of the part. When the junction

temperature goes up to about 150°C, the part will be disabled.

When the junction temperature drops down to about 120°C,

the part will be enabled. With this feature, any short circuit at

the outputs will enable the thermal shutdown circuitry to

disable the part.

POWER SUPPLY BYPASSING AND PRINTED CIRCUIT

BOARD LAYOUT

Good printed circuit board layout is necessary for optimum

performance. A low impedance and clean analog ground plane

should be used for the EL5325A. The traces from the two ground

pins to the ground plane must be very short. The thermal pad of

the EL5325A should be connected to the analog ground plane.

Lead length should be as short as possible and all power supply

pins must be well bypassed. A 0.1µF ceramic capacitor must be

place very close to the VS, VREFH, VREFL, and CAP pins. A

4.7µF local bypass tantalum capacitor should be placed to the VS,

VREFH, and VREFL pins.

APPLICATION USING THE EL5325A

In the first application drawing, the schematic shows the

interconnect of a pair of EL5325A chips connected to give

12 gamma corrected voltages above the VCOM voltage, and

12 gamma corrected voltages below the VCOM voltage.

External Shutdown

The EL5325A also has an external shutdown to enable and

disable the part. The SHDN pin should never be driven low.

Rather, to enable the part, the SHDN pin must be left open

(float). To disable, the SHDN pin must be driven HI (>2V). WIth

this feature, the EL5325A can be forced to shut down,

regardless of any other conditions. A simple open collector

driver is adequate to control the enable and disable function:

VSD

R1

100K

SHDN

R2

100K

Q1

PNP

EL5325A

SHDN

FN7447 Rev 1.00

May 8, 2006

Page 9 of 12

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