HV857
Low Noise, High Voltage EL Lamp Driver IC
Features
Patented audible noise reduction
Patented lamp aging compensation
190 V
PP
output voltage for higher brightness
Patented output timing for high efficiency
Single cell lithium ion compatible
150nA shutdown current
Wide input voltage range 1.8V to 5.0V
Separately adjustable lamp and converter
frequencies
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Output voltage regulation
►
Split supply capability
►
Available in MSOP-8 and DFN-8 packages
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General Description
The Supertex HV857 is a high voltage driver designed for driving
Electroluminescent (EL) lamps of up to 5 square inches. The
input supply voltage range is from 1.8V to 5.0V. The device uses
a single inductor and a minimum number of passive components.
The nominal regulated output voltage that is applied to the EL
lamp is ±95V. The chip can be enabled/disabled by connecting
the resistor on RSW-Osc to VDD/GND.
The HV857 has two internal oscillators, a switching MOSFET,
and a high voltage EL lamp driver. The frequency for the switching
MOSFET is set by an external resistor connected between the
RSW-Osc pin and the supply pin VDD. The EL lamp driver
frequency is set by an external resistor connected between REL-
Osc pin and VDD pin. An external inductor is connected between
the LX and VDD pins or V
IN
for split supply applications. A 0.003-
0.1µF capacitor is connected between CS and ground. The EL
lamp is connected between VA and VB.
The switching MOSFET charges the external inductor and
discharges it into the capacitor at CS. The voltage at CS will
start to increase. Once the voltage at CS reaches a nominal
value of 95V, the switching MOSFET is turned OFF to conserve
power. The outputs VA and VB are configured as an H bridge
and are switching in opposite states to achieve ±95V across the
EL lamp.
Applications
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LCD backlighting
Mobile Cellular Phone
PDAs
Handheld wireless communication products
Global Positioning Systems (GPS)
Typical Application Circuit
ON = V
DD
OFF =
0
Enable Signal
+
V
DD
_
C
DD
1
R
SW
VDD
VA
VB
CS
LX
8
EL Lamp
7
6
D
5
L
X
C
S
2
RSW-Osc
3
R
EL
4
GND
REL-Osc
+
V
IN
_
C
IN
HV857MG
HV857
Ordering Information
Device
HV857
Package Options
8-Lead DFN (K7)
HV857K7-G
8-Lead MSOP (MG)
HV857MG-G
-G indicates package is RoHS compliant (‘Green’)
Absolute Maximum Ratings
Parameter
Supply Voltage, V
DD
Operating Temperature
Storage Temperature
DFN-8 Power Dissipation
MSOP-8 Power Dissipation
Output voltage, V
CS
Value
-0.5V to 6.5V
-40°C to +85°C
-65°C to +150°C
1.6W
300mW
-0.5 to +120V
Pin Configuration
Top View
VDD
1
RSW-Osc
2
8
VA
7
VB
MSOP-8
REL-Osc
3
GND
4
6
CS
5
LX
HV857MG
Absolute Maximum Ratings are those values beyond which damage to the
device may occur. Functional operation under these conditions is not implied.
Continuous operation of the device at the absolute rating level may affect
device reliability. All voltages are referenced to device ground.
VDD
RSW-Osc
REL-Osc
GND
1
2
3
4
8
7
VA
VB
CS
LX
DFN-8
6
5
Thermal Resistance
Package
DFN-8
MSOP-8
Mounted on FR4 board, 25mm x 25mm x 1.57mm
θ
ja
60
O
C/W
330
O
C/W
HV857K7
Pads are at the bottom of the package
Exposed center pad is at ground potential
Recommended Operating Conditions
Symbol
V
DD
f
EL
T
A
Parameter
Supply voltage
Operating drive frequency
Operating temperature
Min
1.8
-
-40
Typ
-
-
-
Max
5.0
1
+85
Units
V
kHz
O
Conditions
---
---
---
C
Enable/Disable Function Table
Symbol
EN-L
EN-H
Parameter
Logic input low voltage
Logic input high voltage
Min
0
V
DD
- 0.2
Typ
-
-
Max
0.2
V
DD
Units
V
V
Conditions
V
DD
= 1.8V to 5.0V
V
DD
= 1.8V to 5.0V
Electrical Characteristics
DC Characteristics
(Over recommended operating conditions unless otherwise specified, T =25°C)
A
Symbol
R
DS(ON)
V
CS
V
A
– V
B
I
DDQ
Parameter
On-resistance of switching transistor
Max. output regulation voltage
Peak to Peak output voltage
Quiescent V
DD
supply current
Min
-
85
170
-
Typ
-
95
190
-
Max
6.0
105
210
150
Units
Ω
V
V
nA
Conditions
I = 100mA
V
DD
=1.8V to 5.0V
V
DD
=1.8V to 5.0V
R
SW-Osc
= Low
2
HV857
Electrical Characteristics (cont.)
Symbol
I
DD
I
IN
V
CS
f
EL
f
SW
D
Parameter
Input current going into the VDD pin
Input current including inductor current
Output voltage on VCS
EL lamp frequency
Switching transistor frequency
Switching transistor duty cycle
Min
-
-
-
205
-
-
Typ
-
20
84
240
80
88
Max
150
25
-
275
-
-
Units
µA
mA
V
Hz
kHz
%
Conditions
V
DD
= 1.8V to 5.0V. See Figure 1
See Figure 1*
See Figure 1
See Figure 1
See Figure 1
See Figure 1
* The inductor used is a 220µH Murata inductor, max DC resistance of 8.4Ω, part # LQH32CN221K21.
Block Diagram
LX
VDD
CS
RSW-Osc
Switch
Osc
Q
GND
Disable
C
VA
+
_
V
REF
V
SENSE
Q
High
Voltage
Level
Translator
Q
VB
Q
V
DD
EL
Osc
REL-Osc
Figure 1: Typical Application/ Test Circuit
ON = V
DD
OFF = 0V
560kΩ
0.1µF
2.0MΩ
4
GND
1
VDD
2
RSW-Osc
3
REL-Osc
Enable Signal
2.0kΩ
VA
8
VB
7
CS
6
BAS21
LX
5
Equivalent to 3.0in
2
lamp
10nF
+
V
DD
-
HV857MG
+
V
IN
4.7µF
220µH*
3.3nF,
100V
-
* Murata Inductor
LQH32CN221K21
3
HV857
Typical Performance
Device
HV857MG-G
Lamp Size
3.0in
2
V
DD
= V
IN
3.3V
I
IN
20.0mA
V
CS
84V
f
EL
240Hz
Brightness
6.0ft-lm
Typical Performance Curves for Figure 1
(EL Lamp = 3.0in , V
2
DD
= 3.0V)
V
CS
vs V
IN
95
V
CS
(V)
l
IN
(mA)
I
IN
vs V
IN
25
23
21
19
17
15
13
1.5
85
75
65
55
1.5
2.5
3.5
V
IN
(V)
4.5
5.5
2.5
3.5
V
IN
(V)
4.5
5.5
Brightness vs V
IN
7
6
5
4
3
2
1
1.5
24
22
Brightness (ft-lm)
I
IN
vs V
CS
l
IN
(mA)
20
18
16
2.5
3.5
V
IN
(V)
4.5
5.5
14
55
65
75
V
CS
(V)
85
95
I
IN
, V
CS
, Brightness vs Inductor Value
100
90
6
80
70
V
CS
5
Brightness
4
3
Iin
2
7
60
50
40
30
20
10
0
100
l
IN
1
0
150
200
250
300
350
400
450
500
550
600
Inductor Value (µH)
4
Brightness (ft-lm)
lin (mA), V
CS
(V)
HV857
External Component Description
External
Component
Diode
C
S
Capacitor
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
EL
resistor connected between REL-Osc and VDD
of the device. The lamp frequency increases as R
EL
decreases. As the EL lamp frequency increases,
the amount of current drawn from the battery will increase and the output voltage V
CS
will decrease. The
color of the EL lamp is dependent upon its frequency.
R
EL
Resistor
A 2MΩ resistor would provide lamp frequency of 205 to 275Hz. Decreasing the R
EL
resistor by a factor
of 2 will increase the lamp frequency by a factor of 2.
f
EL
=
(2MΩ)(240Hz)
R
EL
R
SW
Resistor
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
SW
decreases. With a given inductor, as
the switching frequency increases, the amount of current drawn from the battery will decrease and the
output voltage, V
CS
, will also decrease.
f
SW
=
(560kΩ)(80kHz)
R
SW
L
X
Inductor
The inductor L
X
is used to boost the low input voltage by inductive flyback. When the internal switch is
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
S
. The energy stored in the capacitor is connected to the
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
SW
) should be increased to avoid saturation.
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
SW
resistor value
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
IN
x I
IN
), will also increase. If the input power is greater than
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.
Lamp
5
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