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MAX4990E

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

Maxim Integrated 

High-Voltage, ±15kV ESD-Protected

Electroluminescent Lamp Driver

±15kV ESD Protection

As with all Maxim devices, ESD-protection structures

are incorporated on all pins to protect against electro-

static discharges encountered during handling and

assembly. The EL lamp driver outputs of the MAX4990E

have extra protection against static electricity. Maxim’s

engineers have developed state-of-the-art structures to

protect these pins against ESD of ±15kV without dam-

age. The ESD structures withstand high ESD in all

states: normal operation, shutdown, and powered

down. After an ESD event, the MAX4990E keep working

without latchup or damage.

ESD protection can be tested in various ways. The

transmitter EL lamp outputs of the MAX4990E are char-

acterized for protection to the following limits:

• ±15kV using the Human Body Model

• ±4kV IEC 61000-4-2 Contact Discharge

• ±15kV IEC 61000-4-2 Air-Gap Discharge

ESD Test Conditions

ESD performance depends on a variety of conditions.

Contact Maxim for a reliability report that documents

test setup, test methodology, and test results.

Human Body Model

Figure 1a shows the Human Body Model, and Figure

1b shows the current waveform it generates when dis-

charged into a low impedance. This model consists of

a 100pF capacitor charged to the ESD voltage of inter-

est, which is then discharged into the test device

through a 1.5kΩ resistor.

IEC 61000-4-2

The IEC 61000-4-2 standard covers ESD testing and

performance of finished equipment. However, it does

not specifically refer to integrated circuits. The

MAX4990E assists in designing equipment to meet IEC

61000-4-2 without the need for additional ESD-protec-

tion components.

The major difference between tests done using the

Human Body Model and IEC 61000-4-2 is higher peak

current in IEC 61000-4-2 because series resistance is

lower in the IEC 61000-4-2 model. Hence, the ESD

withstand voltage measured to IEC 61000-4-2 is gener-

ally lower than that measured using the Human Body

Model. Figure 1c shows the IEC 61000-4-2 model, and

Figure 1d shows the current waveform for IEC 61000-4-

2 ESD Contact Discharge test.

Machine Model

The machine model for ESD tests all pins using a 200pF

storage capacitor and zero discharge resistance.

The objective is to emulate the stress caused when I/O

pins are contacted by handling equipment during test

and assembly. Of course, all pins require this protection.

The Air-Gap test involves approaching the device with a

charged probe. The Contact Discharge method connects

the probe to the device before the probe is energized.

Design Procedure

LX Inductor Selection

The recommended inductor values are 220µH/330µH.

For most applications, series resistance (DCR) should

be below 8Ω for reasonable efficiency. Do not exceed

the inductor’s saturation current.

RSLEW Resistor Selection

To help reduce audible noise emission by the EL lamp,

the MAX4990E features a slew-rate control input

(SLEW) that allows the user to set the slew-rate of the

high-voltage outputs, VA and VB, by connecting a

resistor, RSLEW, from the SLEW input to GND. RSLEW

precisely sets the reference current IB that is used to

charge and discharge the capacitances at the SW

input and EL input, and is used as a reference current

for internal circuitry. The reference current is related to

RSLEW by the following equation: IB = 1V/RSLEW.

Decreasing the value of RSLEW increases IB and

increases the slew rate at the EL lamp output. Increasing

the value of RSLEW decreases IB and decreases the

slew rate at the EL lamp output. The output slew rate is

related to RSLEW by the following equation:

⎛

SlewRate⎝⎜

V

100μs

⎞

⎠⎟

=

11.25

RSLEW (MΩ)

The ideal value for a given design varies depending on

lamp size and mechanical enclosure. Typically, the best

slew rate for minimizing audible noise is between

10V/100µs and 20V/100µs. This results in RSLEW values

ranging from 1.125MΩ to 0.5625MΩ. For example, if the

desired slew rate is 20 (V/100µs), this leads to an RSLEW

resistor value in MΩ of RSLEW = 11.25/20V = 0.5625MΩ.

Note: Connecting RSLEW to GND will not damage the

device. However, for the device to operate correctly,

RSLEW should be in the 100kΩ to 2.2MΩ range.

RSLEW also affects the frequency of the boost converter

(see the CSW Capacitor Selection), the frequency of the

EL lamp (see the CEL Capacitor Selection section), and

the peak-to-peak voltage of the EL lamp.

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