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MAX14514

Dual Electroluminescent Lamp Driver

Maxim Integrated 

MAX14514

Dual Electroluminescent Lamp Driver

Detailed Description

The MAX14514 high-voltage DC-AC converter is designed

to drive two EL lamps. The MAX14514 features a +2.7V

to +5.5V input range that allows the device to accept a

wide variety of voltage sources, including single-cell Li+

batteries. The lamp outputs of the device generate up to

300VP-P for maximum lamp brightness. The slew rate,

frequency, and peak-to-peak voltage of the MAX14514 EL

lamp outputs are programmed through a combination of

external components and/or logic inputs.

Output Slew Rate

The MAX14514 uses the resistor RSLEW to set a refer-

ence current for the internal circuitry. The reference cur-

rent directly affects the slew rate of the EL lamp output.

Increasing the value of RSLEW decreases the slew rate,

and decreasing the value of RSLEW increases the slew

rate. (See the RSLEW Resistor Selection section on how

to select RSLEW.)

Output Frequency

The MAX14514 uses an internal oscillator to set the

desired output frequency. The output frequency is adjust-

ed by either 1) the combination of a resistor from SLEW to

GND and an external capacitor from the EL input to GND,

or 2) by driving a clock signal directly into the EL input.

(See the CEL Capacitor Selection section for choosing the

CEL capacitor value.)

Dimming Control

The MAX14514 features dimming control inputs, DIM1

and DIM2, to control the peak-to-peak voltages on lamp

outputs V1, V2, and COM. DIM_ is controlled by either

a DC voltage, a PWM signal, or a resistor from DIM_ to

GND. (See the RDIM Resistor Selection section.)

Applying a DC voltage to DIM_ ranging from VLPD to VIH_

DIM_ linearly varies the corresponding output voltage from

130V to 300V. Increasing the voltage on DIM_ increases

the peak-to-peak output, and decreasing the voltage on

DIM_ decreases the peak-to-peak output voltage. Note

that when VDIM_ goes below VIL_DIM_, the corresponding

output turns off.

DIM_ features an internal lowpass filter to allow a PWM

signal to control the output voltage. Voltages on DIM_

are internally level translated down to VIH_DIM_, so

that the equivalent voltage on DIM_ is (%duty cycle) x

VIH_DIM_. The DIM_ inputs accept the 200kHz to 1MHz

frequency range. Note that for PWM signals, the logic

voltage applied to DIM_ must be greater than or equal to

VIH_DIM_.

The peak-to-peak EL lamp output voltage is related to

VDIM_ (for VDIM_ > VIL_DIM_) or PWM duty cycle by the

following equation:

V_ - VCOM = 260 x (VDIM_) = 260 x (%duty cycle) x

(VIH_DIM_)

Slow Turn-On, Slow Turn-Off

The MAX14514 provides a slow turn-on and slow turn-off

time feature that is enabled by connecting a capacitor from

CAP to GND (see the Typical Application Circuit and the

CCAP Capacitor Selection section). This slow turn-on/-off

feature causes the peak-to-peak voltage of the EL outputs

to slowly rise or fall any time the outputs are enabled or

disabled, either through EN or DIM_ (see Table 1). The

slow rise and fall of the peak-to-peak EL output voltage

creates a soft fade-on and fade-off of the EL lamp, rather

than an abrupt change in brightness. To disable the slow

turn-on/turn-off feature, connect CAP to VDD.

Table 1. Slow Turn-On, Slow Turn-Off

LOGIC INPUT

EL OUTPUTS*

EN

1≥0

DIM1

1

DIM2

1

V1

Slow Turn-Off

V2

Slow Turn-Off

0≥1

1

1

Slow Turn-On Slow Turn-On

1

1≥0

X

Slow Turn-Off

X

1

0≥1

X

Slow Turn-On

X

1

X

1≥0

X

Slow Turn-Off

1

X

0≥1

X

Slow Turn-On

*With capacitor from CAP to GND (CAP is not connected to VDD).

X = Don’t Care.

Boost Converter

The MAX14514 boost converter consists of an external

inductor from VDD to the LX input, an internal DMOS

switch, an external diode from LX to the CS output, an

external capacitor from the CS output to GND, and the

EL lamps, CLAMP1 and CLAMP2, connected to the EL

lamp outputs. When the DMOS switch is turned on, LX is

connected to GND, and the inductor is charged. When the

DMOS switch is turned off, the energy stored in the induc-

tor is transferred to the capacitor CCS and the EL lamps.

Note: Keeping SW high shorts LX to GND and causes the

internal die temperature to increase. The MAX14514 is

protected by entering a thermal-shutdown state (see the

Thermal Short-Circuit Protection section).

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