MAX4990E Просмотр технического описания (PDF) - Maxim Integrated

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MAX4990E

High-Voltage, ±15kV ESD-Protected Electroluminescent Lamp Driver

Maxim Integrated 

High-Voltage, ±15kV ESD-Protected

Electroluminescent Lamp Driver

lamp outputs. A slow turn-on effect is produced by dri-

ving EN high. Slow turn-on/-off time is related by the fol-

lowing equation:

tON = 2.6 x RDIM x CDIM

tOFF = 1.2 x RDIM x CDIM

For this equation to be valid, RDIM/RSLEW must be

≤ 1.3.

CCS Capacitor Selection

CCS is the output of the boost converter and provides

the high-voltage source for the EL lamp. Connect a

3.3nF capacitor from CS to GND and place as close to

the CS input as possible. When using an inductor value

larger than 220µH, it may be necessary to increase the

CCS. For a LX = 470µH and CLAMP = 20nF, a CCS

ranging from 3.3nF to 6.8nF is recommended.

CEL Capacitor Selection

The MAX4990E EL lamp output frequency is set by

connecting a capacitor from the EL input to GND

together with a resistor from SLEW to GND or by driving

the EL input with an external clock (0 to +1.5V). The EL

lamp output frequency is related to the CEL capacitor

by the following equation:

fEL

=

0.0817

RSLEW × CEL

For example, an RSLEW = 375kΩ and a CEL capacitor

value of 1000pF equals an EL lamp output frequency of

FEL = 217Hz.

CSW Capacitor Selection

The boost converter switching frequency is set by con-

necting a capacitor from the SW input to GND, together

with the resistance from the SLEW input to GND, or driving

the SW input with an external clock (0 to +1.5V). The

switching frequency of the boost converter is related to the

capacitor from SW to GND by the following equation:

fSW

=

3.61

RSLEW × CSW

Connect the SW input to GND to turn the switch oscilla-

tor of the boost converter off. Although the optimal fSW

depends on the inductor value, the suggested fSW

range is 20kHz to 150kHz.

Note: Driving SW with a logic-high causes LX to be dri-

ven to GND. Keeping SW high shorts LX to GND, caus-

ing the internal die temperature to increase. The

MAX4990E is protected by entering a thermal-shutdown

state. (See the Thermal Short-Circuit Protection section.)

CB Capacitor Selection

Bypass VDD with a 0.1µF ceramic capacitor as close to

the IC as possible and a 4.7µF ceramic capacitor as

close to the inductor as possible

Diode Selection

Connect a diode, D1, from the LX node to CS to rectify

the boost voltage on CS. The diode should be a fast-

recovery diode that is tolerant to +150V.

EL Lamp Selection

EL lamps have a capacitance of approximately 2.5nF to

3.5nF per square inch. The MAX4990E effectively

charges capacitance ranging from 2nF to 20nF.

Applications Information

PCB Layout

Keep PCB traces as short as possible. Ensure that

bypass capacitors are as close to the device as possi-

ble. Use large ground planes where possible.

Chip Information

PROCESS: BiCMOS-DMOS

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