Datasheet

MAX4990
±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 MAX4990
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 MAX4990 keep working
without latchup or damage.
ESD protection can be tested in various ways. The
transmitter EL lamp outputs of the MAX4990 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 interest,
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
MAX4990 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 with-
stand voltage measured to IEC 61000-4-2 is generally
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.
R
SLEW
Resistor Selection
To help reduce audible noise emission by the EL lamp,
the MAX4990 features a slew-rate control input (SLEW)
that allows the user to set the slew-rate of the high-volt-
age outputs, V
A
and V
B,
by connecting a resistor,
R
SLEW
, from the SLEW input to GND. R
SLEW
precisely
sets the reference current I
B
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 cir-
cuitry. The reference current is related to R
SLEW
by the
following equation: I
B
= 1V/R
SLEW
. Decreasing the
value of R
SLEW
increases I
B
and increases the slew rate
at the EL lamp output. Increasing the value of R
SLEW
decreases I
B
and decreases the slew rate at the EL lamp
output. The output slew rate is related to R
SLEW
by the
following equation:
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 R
SLEW
values
ranging from 1.125MΩ to 0.5625MΩ. For example, if the
desired slew rate is 20 (V/100µs), this leads to an R
SLEW
resistor value in MΩ of R
SLEW
= 11.25/20V = 0.5625MΩ.
Note: Connecting R
SLEW
to GND will not damage the
device. However, for the device to operate correctly,
R
SLEW
should be in the 100kΩ to 2.2MΩ range.
R
SLEW
also affects the frequency of the boost converter
(see the C
SW
Capacitor Selection ), the frequency of the
EL lamp (see the C
EL
Capacitor Selection section), and
the peak-to-peak voltage of the EL lamp.
SlewRate
V
sR M100
125
μ
⎛
⎝
⎜
⎞
⎠
⎟
=
()
1
SLEW
.
Ω
High-Voltage, ±15kV ESD-Protected
Electroluminescent Lamp Driver
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