HV857K7-G Supertex, HV857K7-G Datasheet - Page 5

• Manufacturer Part Number: HV857K7-G
• Description: Display Drivers High Voltage Low Noise EL Lamp
• Manufacturer: Supertex

Specifications of HV857K7-G

• Driver Type: EL Lamp Drivers
• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• Package / Case: DFN-8
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

External Component Description
C
Component
R
R
L
S
SW
External
EL
X
Capacitor
Diode
Lamp
Inductor
Resistor
Resistor
Description
Fast reverse recovery diode, BAS21 diode or equivalent.
0.003µF to 0.1µF, 100V capacitor to GND is used to store the energy transferred from the inductor.
The EL lamp frequency is controlled via an external R
of the device. The lamp frequency increases as R
the amount of current drawn from the battery will increase and the output voltage V
color of the EL lamp is dependent upon its frequency.
A 2MΩ resistor would provide lamp frequency of 205 to 275Hz. Decreasing the R
of 2 will increase the lamp frequency by a factor of 2.
The switching frequency of the converter is controlled via an external resistor, RSW between RSW-Osc
and VDD of the device. The switching frequency increases as R
the switching frequency increases, the amount of current drawn from the battery will decrease and the
output voltage, V
The inductor L
on, the inductor is being charged. When the internal switch is off, the charge stored in the inductor will
be transferred to the high voltage capacitor C
internal H-bridge, and therefore to the EL lamp. In general, smaller value inductors, which can handle
more current, are more suitable to drive larger size lamps. As the inductor value decreases, the switch-
ing frequency of the inductor (controlled by R
A 220µH Murata (LQH32CN221) inductor with 8.4Ω series DC resistance is typically recommended. For
inductors with the same inductance value, but with lower series DC resistance, lower R
is needed to prevent high current draw and inductor saturation.
As the EL lamp size increases, more current will be drawn from the battery to maintain high voltage
across the EL lamp. The input power, (V
the power dissipation of the package, an external resistor in series with one side of the lamp is recom-
mended to help reduce the package power dissipation.
X
●
is used to boost the low input voltage by inductive flyback. When the internal switch is
CS
1235 Bordeaux Drive, Sunnyvale, CA 94089
, will also decrease.
f
SW
f
EL
=
=
(560kΩ)(80kHz)
(2MΩ)(240Hz)
IN
5
R
R
x I
EL
SW
SW
S
IN
. The energy stored in the capacitor is connected to the
) should be increased to avoid saturation.
), will also increase. If the input power is greater than
EL
EL
decreases. As the EL lamp frequency increases,
●
resistor connected between REL-Osc and VDD
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SW
decreases. With a given inductor, as
●
www.supertex.com
EL
CS
resistor by a factor
will decrease. The
SW
resistor value
HV857