MAX14521E_15 Datasheet, PDF (10/21 Pages) Maxim Integrated Products – Quad, High-Voltage EL Lamp Driver with I2C Interface

MAX14521E
Quad, High-Voltage EL Lamp Driver
with I²C Interface
Boost Converter
The MAX14521E boost converter consists of an exter-
nal- tapped inductor from V_DD to the LX input, an internal
DMOS switch, an external diode from the secondary of
the tapped inductor to the CS output, an external capaci-
tor from the CS output to GND, and an EL lamp con-
nected 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 inductor is transferred to the capacitor C_CS
and the EL lamp.
Note: The MAX14521E exhibits high-voltage spikes on
the LX node. The addition of a snubber circuit to the LX
node protects the device by suppressing the highvoltage
spikes. The values of RSN and CSN should be optimized
for the specific tapped inductor used. Typical values are
R_SN = 20Ω and C_SN = 330pF.
The MAX14521E boost-converter frequency uses an
internal oscillator to set the frequency of the boost
converter. The oscillator frequency is adjusted by the
FSW[4:0] bits of the boost-converter frequency register.
The boost converter increases and decreases linearly
with FSW[3:0].
To further reduce the amount of EMI/EFI generated by the
circuit, the boost-converter frequency can be modulated
(see the SS[1:0] bits of the boost-converter frequency
register). Enabling modulation spreads the switching
energy of the oscillator in the frequency domain, thus
decreasing EMI.
Independent Dimming Control
The brightness of an EL lamp is proportional to the peak-
to-peak voltage applied across the lamp. The MAX14521E
provides four registers to control the EL peak-to-peak volt-
age of each EL output using the EL_ _[4:0] bits of the EL
ramping time and EL peak voltage registers.
EL Output Waveshape
The MAX14521E can produce sine-wave to squarewave
waveshapes on the EL output by varying the slope of the
EL output. This is achieved by using bits SL[1:0] of the EL
shape register. If the EL shape configuration is set to sine
and if all EL outputs have the same amplitude settings,
then each EL output has a sinusoidal waveshape. If the
EL outputs have different amplitude settings, then the EL
output with the highest setting has a sine waveshape while
the remaining EL outputs have a clamped sine waveshape.
Auxiliary Audio Input (AUX)
The MAX14521E uses an auxiliary input AUX that accepts
an audio signal to produce visual effects on the EL out-
puts. The frequency and amplitude modulation (FR_AM)
bit is set to modulate the EL output voltage or frequency.
The AUX audio signal modulates the EL output voltage
when FR_AM is set to 0 and modulates the EL output
frequency when FR_AM is set to 1.
When the NO_SAMPLE bit is enabled, the voltage of
the EL outputs is proportional to the voltage at AUX. For
example, when FR_AM = 0, NO_SAMPLE = 1, and any of
the AU1, AU2, AU3, AU4 bits are set to 1, the peak value
of those particular channels follow AUX directly.
If AUX is a DC value, the EL output voltage is V_EL = 250
x AUX (V_P-P) with a maximum of 300V_P-P.
AUX can also accept a PWM signal with a frequency rang-
ing from 100kHz to 10MHz, where the EL output voltage
is V_EL = 300 x DutyCycle% (V_P-P). The NO_SAMPLE bit
has no effect when FR_AM = 1.
When FR_AM = 1, frequency modulation is enabled and
the AUXDIV1 and AUXDIV0 bits are used to divide the
audio frequency and apply this to the EL outputs. AU1,
AU2, AU3, and AU4 must be set to 1 to enable this feature.
Shutdown
The MAX14521E features two methods to place the
device in shutdown: 1) a reset input, RB, to clear all reg-
isters to zero and put the device into low-power shutdown
mode, and 2) the EN bit of the system register. Using
method 1, the device does not respond to I²C commu-
nications when RB is held low. Using method 2, the EL
outputs are shut down; however, the register contents
remain unchanged.
Undervoltage Lockout (UVLO)
The MAX14521E has a UVLO threshold of +2.0V (typ).
When V_DD falls below +2.0V (typ), the device enters a
nonoperative mode. The contents of the I²C registers are
not guaranteed below UVLO.
Thermal Protection
The MAX14521E enters a nonoperative mode if the internal
die temperature of the device reaches or exceeds +160°C
(typ). The MAX14521E is latched, and only placing RB to
0 resets the thermal protection bit as well as all registers.
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