HV857L
Low Noise, High Voltage EL Lamp Driver IC
Features
►
►
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►
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Audible noise reduction
190 V
PP
output voltage for higher brightness
Single cell lithium ion compatible
150nA shutdown current
Wide input voltage range 1.8V to 5.0V
Separately adjustable lamp and converter
frequencies
►
Output voltage regulation
►
Split supply capability
►
Available in DFN-8 and MSOP-8 packages
General Description
The Supertex HV857L is a low noise, high voltage driver
designed for driving Electroluminescent (EL) lamps of up to five
square inches. It is the low noise version of the EL lamp driver
HV857. 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/ground.
The HV857L 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 the REL-Osc and VDD pins. An external inductor is
connected between the LX and VDD pins, or VIN for split supply
applications. A 0.003-0.1µF capacitor is connected between CS
and ground. The EL lamp is connected between the VA and VB
pins.
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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Mobile cellular phones
Keypad backlighting
LCD backlighting
PDAs
Handheld wireless communication products
Global Positioning Systems (GPS)
Typical Application Circuit
ON = V
DD
OFF =
0
Enable Signal
+
V
DD
_
+
V
IN
_
C
DD
1
R
SW
2
3
VDD
RSW-Osc
REL-Osc
GND
VA
VB
CS
LX
8
EL Lamp
7
6
D
5
C
S
L
X
C
IN
R
EL
4
HV857LMG
HV857L
Ordering Information
Device
HV857L
Package Options
8-Lead DFN (K7)
HV857LK7-G
8-Lead MSOP (MG)
HV857LMG-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
7
VA
VB
CS
LX
MSOP-8
REL-Osc
3
GND
4
6
5
HV857LMG
VDD
RSW-Osc
REL-Osc
1
2
3
4
8
VA
VB
CS
LX
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.
DFN-8
7
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
GND
HV857LK7
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
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
A
= 25°C)
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
HV857L
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
-
-
-
175
65
-
Typ
-
25
92
205
77
88
Max
150
40
-
235
89
-
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
_
V
REF
V
SENSE
High
Voltage
Level
Trans-
lators
Q
VA
V
DD
EL
Osc
Q
REL-Osc
VB
Q
Figure 1: Typical Application/ Test Circuit
ON = V
DD
OFF = 0V
3.0in
2
EL lamp
1
2
3
Enable Signal
+
V
DD
560kΩ
0.1µF
VDD
RSW-Osc
REL-Osc
VA
8
VB
7
CS
6
BAS21
LX
5
-
2.0MΩ
4
GND
+
V
IN
HV857LMG
4.7µF
220µH*
3.3nF,
100V
-
* Murata Inductor
LQH32CN221K21
3
HV857L
Typical Performance
Device
HV857LMG-G
Lamp Size
3.0in
2
V
DD
= V
IN
3.3V
I
IN
25.40mA
V
CS
92V
f
EL
205Hz
Brightness
5.70ft-lm
Typical Performance Curves for Figure 1
(EL Lamp = 3.0in , V
2
DD
= 3.0V)
V
CS
vs V
IN
105
85
75
65
55
1.5
2.5
3.5
4.5
5.5
33
I
IN
vs V
IN
I
IN
(mA)
28
23
18
13
1.5
2.5
3.5
4.5
5.5
V
CS
(V)
95
Vin (V)
Brightness vs V
IN
7
6
5
4
3
2
1
1.5
2.5
3.5
4.5
5.5
V
IN
(V)
I
IN
vs V
CS
34
Brightness (ft-lm)
I
IN
(mA)
29
24
19
14
55
65
75
85
95
105
V
IN
(V)
V
CS
(V)
Typical Waveform on V
A
, V
B
and Differential Waveform V
A
- V
B
4
HV857L
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 205Hz. Decreasing the R
EL
resistor by a factor of 2 will
increase the lamp frequency by a factor of 2.
f
EL
=
(2MΩ)(205Hz)
R
EL
R
SW
Resistor
The switching frequency of the converter is controlled via an external resistor, R
SW
, 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.
(560kΩ)(77kHz)
R
SW
f
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, a 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
Split Supply Configuration
The HV857L can also be used for handheld devices operat-
ing from a battery where a regulated voltage is available.
This is shown in Figure 2. The regulated voltage can be used
to run the internal logic of the HV857L. The amount of cur-
rent necessary to run the internal logic is 150µA maximum at
a V
DD
of 5.0V. Therefore, the regulated voltage could easily
provide the current without being loaded down.
Enable/Disable Configuration
The HV857L can be easily enabled and disabled via a logic
control signal on the R
SW
and R
EL
resistors as shown in Fig-
ure 2 below. The control signal, which can be from a micro-
processor, has to track the V
DD
supply. R
SW
and R
EL
are typi-
cally very high values. Therefore, only 10’s of microamperes
will be drawn from the logic signal when it is at a logic high
(enable) state. When the microprocessor signal is high, the
device is enabled, and when the signal is low, it is disabled.
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