HV895DB1
Inductorless,
Liquid Lens Driver Demoboard
General Description
The HV895DB1 is designed to drive liquid lenses of up to
200pF with a 1.5kHz waveform at amplitudes up to 59.7V
RMS
,
controlled via an I
2
C interface.
A charge pump boost converter integrated on-chip provides
the high voltage necessary for driving the lens. No external
inductors or diodes are needed. Two ceramic chip capacitors
are the only external components required for a complete lens
driver circuit.
An H-bridge output stage provides AC drive to the lens,
allowing the use of a single high voltage boost converter while
providing alternating polarity to the lens. Controlled rising and
falling edges on the drive waveform reduces EMI.
Specifications
Supply voltage (V
IN
)
:
Supply current (I
IN
)
:
Output voltage (OUT1 – OUT2)
:
Load (lens) capacitance
:
I
2
C reference voltage (V
DD
)
:
I
2
C clock
:
I
2
C address (7-bit):
2.65 – 5.50V
20mA max operating
500nA max standby
9.6 – 59.7V
RMS
,
adjustable via I
2
C
100 – 200pF
1.70 – 2.95V
400kHz max
0100011b
Board Layout and Connection Diagram
V
DD
1.70 – 2.95V
SCL
SDA
Liquid Lens
100 – 200pF
I
2
C bus
V
IN
2.65 – 5.5V
Actual Dimensions: 28.0mm x 30.7mm
Connections:
VIN
Supply voltage to the HV895. Externally supplied V
IN
should
be between 2.65 and 5.50V.
GND
Circuit common.
VDD
Externally supplied logic reference voltage for the I
2
C inter-
face. V
DD
should be between 1.70 and 2.95V.
SCL
I
2
C clock. Clock frequency should be no greater than
400kHz.
SDA
I
2
C data.
OUT1
and
OUT2
The lens driver output. Connect the lens between these two
terminals. Load (lens) capacitance should be between 100
and 200pF, including any stray capacitance.
Note:
The resistors shown in the connection diagram are the
normal I
2
C pull-ups. No additional pull-ups are required.
1
HV895DB1
HV895DB1 Circuit Schematic
I2C bus
V
DD
1.70 – 2.95V
VDD
SDA
SCL
V
IN
2.65 – 5.5V
VIN
C
IN
2.2µF
GND
HV895DB1
IC
1
VDD
SDA
SCL
VIN1
VIN2
C
HV
4.7nF
OUT1
OUT1
OUT2
Liquid Lens
100 – 200pF
HV895
OUT2
HV
GND1 GND2
Bill of Materials
Part
C
IN
C
HV
IC
1
Description
2.2μF ceramic capacitor
4.7nF ceramic capacitor
Lens driver
Tolerance
20%
10%
-
Rating
6.3V
100V
-
Package
0402
0402
1 × 6mm
Manufacturer Part Number
Any
MuRata
Tecate
Supertex
---
GRM155R72A472KA01
CMC-100/472KX0402
HV895BD
Operation
A single byte (AMP) written to the HV895 controls the opera-
tion of the driver. Setting AMP = 00h causes the HV895 to
go into low power standby mode. Setting AMP = 01h to FFh
controls output amplitude in 255 monotonic steps.
V
OUT(RMS)
= 9.4V
RMS
+ AMP • 197mV
RMS
The HV895 is write-only. No readback of the AMP byte is
possible.
The HV895’s 7-bit address is 0100011b. For large quantity
orders, other 7-bit addresses may be obtained.
The resistors shown on the above schematic are the I
2
C bus’
normal pull-ups. No additional pull-ups are required. Exter-
nally supplied V
DD
is the I
2
C bus’ reference voltage.
Externally supplied V
IN
should be ramped up in less than
2.0ms to ensure the driver starts-up in standby mode. If
brought up slower, the driver may not start-up in standby
mode, with output amplitude at an indeterminate level. In
this case, writing AMP = 00h brings the driver to standby
mode. No damage will occur if V
IN
is brought up slower than
2.0ms.
Loads less than 100pF may result in waveform distortion.
This is due to the output pins being held at a high-Z state for
a portion of the waveform. Without adequate capacitance
to hold up the voltage, some droop may be observed when
DC-loaded by oscilloscope probes.
To avoid loading down the outputs, be sure to use instru-
ments having at least 10MΩ input impedance when taking
measurements. While many voltmeters may have a very
high input resistance on the DC scale, they frequently have
only 1.0MΩ input impedance on the AC scale. Also, be sure
to use a voltmeter with true RMS capability.
032108
2
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