CPC6826 Datasheet, PDF (9/12 Pages) Clare, Inc. – High Voltage EL Lamp Driver

4. Functional Description
L1
V+
IN
1 (V_DD)
CPC6826
R_SW
2 (R_SW-osc)
Switch
Osc
Q
R_EL
3 (R_EL-osc)
Disable
+
Vsen
- _Vref
Q
Output
Osc
C_IN
Q
V-
IN
4 (GND)
Q
CPC6826
D1
C_OUT
5 (L_X)
6 (C_S)
8 (V_A)
EL Lamp
7 (V_B)
4.1 Overview
The CPC6826 is an EL lamp driver designed for
battery applications operating from an input supply
voltage range of 1.8V to 3.5V and generating an AC
output voltage of 180V_p-p. The device is capable of
driving lamp panels ranging from 1 in² to 5 in².
The CPC6826 IC main block architecture is made up
of two independent oscillators, which control the
switching of a power MOSFET and an H-bridge.
Adjustment of two external resistors, R_SW and R_EL,
sets the frequencies of the oscillators, thus allowing
the designer to maximize efficiency and to increase
the brightness of the lamp.
To conserve supply power and extend battery life, the
CPC6826 automatically shuts down the switcher
circuit whenever switcher output power exceeds load
requirements. Supply power can also be conserved
manually by disabling the switching circuit: pull pin 2,
R_SW, to ground.
4.2 Regulation
The circuit configuration is based on simple boost
converter topology. This method provides excellent
efficiency, minimizes loss of energy, and allows
smaller components to be used in the design. Only a
few passive components (an inductor, a capacitor, two
resistors, and a diode) are required to complete the
simple boost switcher circuit.
When power is applied to V_DD, the internal feedback
voltage V_SEN is less than V_REF causing the
comparator output to go low, which enables the
switching power MOSFET oscillator. When turned on,
the internal low impedance switching MOSFET
causes current to flow through the external inductor.
With current flowing in the inductor, the switching
MOSFET is turned off causing a flyback voltage to
develop across the inductor. As the inductor's flyback
voltage increases to a level greater than a diode drop
above the voltage across the capacitor on the C_S pin,
charge stored in the inductor is transferred into the
C_OUT capacitor. This operating cycle continues until
the V_SEN voltage is above the V_REF in which case the
comparator disables the Switch Oscillator.
The internal high voltage H-Bridge section is enabled
by external resistor R_EL at pin 3 and V_DD on pin 1. The
H-bridge operation is controlled by output oscillator
waveforms driving H-bridge high-side and low-side
MOSFETs. Selecting the value of R_EL allows the
designer to set the frequency of the internal oscillator
to meet design requirements. By alternately switching
the terminals of the lamp between high voltage supply
and ground the 180V_P-P potential develops across the
EL lamp.
R00C
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