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PDF A3907 Data sheet ( Hoja de datos )
| Número de pieza | A3907 | |
| Descripción | Low Voltage Voice Coil Motor Driver | |
| Fabricantes | Allegro | |
| Logotipo |  |
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A3907
Low Voltage Voice Coil Motor Driver
Features and Benefits
▪ WLCSP package for minimum footprint
▪ Ramp control circuit
▪ Fixed I2C logic thresholds
▪ 10-bit D-to-A converter
▪ 100 μA resolution
▪ Low voltage I2C serial interface
▪ Low current draw sleep mode-active low
▪ 2.3 to 5.5 V operation
Applications:
▪ Camera focus motor
Description
Designed for linear control of small form factor voice coil
motors, theA3907 is capable of peak output currents to 102 mA
and operating voltages to 5.5 V.
Internal circuit protection includes thermal shutdown with
hysteresis, flyback clamp diode, and undervoltage monitoring
of VDD.
Package: 6-Bump Chip Scale Package
(suffix CG)
Functional Block Diagram
1.8 V
1.8 kΩ
1.8 kΩ
VDD
SDA
SCL
SLEEPZ
Bandgap
Ref
I2C Serial
Interface
10 Bit DAC
Control
Logic
Timer
2.3 to
5.5V
IOUT
1.2 Ω
GND
A3907-DS, Rev. 1
1 page  
A3907
Low Voltage Voice Coil Motor Driver
Functional Description
Output Current Level Control
The A3907 output current level, IOUT , is controlled dynamically
by programming the D-to-A converter (DAC) value via the I2C
serial port. A 10-bit Level Control code, having a decimal equiva-
lent value from 0 through 1023, is clocked into the SDA pin.
The target output current can be calculated by:
IOUT = nDAC × 100 μA ,
(1)
where nDAC is the decimal equivalent of the Level Control code.
For example, a code of 5 (000001012) sets an output current
target of 500 μA.
Programming Level Control code 0 disables the output sink
drive. In addition, the DAC is automatically set to code 0 at
power-up and also at a fault condition on VDD.
Output Current Slew Rate Control
When a new current level control instruction is received on the
SDA input, the A3907 moves to the new target currrent level by
incrementing or decrementing through each of the intermediate
current levels until it arrives at the new programmed value.
The control instruction received at the SDA input includes both
the 10-bit Level Control code and a 4-bit Ramp Control code.
The Level Control code is used to determine the absolute value of
the changes in IOUT (see equation 1), and the Ramp Control code
maps to a lookup table of time intervals (represented in table 1).
Together, these two codes determine the shape of the current level
change function.
Step or Ramp Function The A3907 can change to the new
target level using either a step or a ramp slew rate function. When
a step function is selected, the A3907 moves to the new target
level without imposing any additional time delays between DAC
updates. To select a step function, program one of the four Ramp
Control codes in table 1 that disable the ramp feature.
When a ramp function is selected, the A3907 imposes time delays
between each DAC update, calculated according to the particular
function option selected. To select a ramp function, program one
of the twelve Ramp Control codes in table 1 that enable the ramp
feature.
Single or Dual Subintervals For either the step or the ramp
slew rate method, the total change can be accomplished in either
one continuous time interval, or divided over two sequential time
subintervals. When the single-interval method is selected, the total
change in IOUT is accomplished over the total time interval deter-
mined by the Rate Control code in table 1, calculated as follows:
CodeT = |(CodeNewTarget – CodePreviousTarget)| / 2 ,
and
(2)
T = CodeT × tdT ,
(3)
where tdT is the delay factor, in table 1.
When the dual-subintervals method is selected, the elapsed time
for each subinterval is determined separately by the Rate Con-
trol code in table 1. The time interval from initiation, T0, to the
switchover point, T1, is calculated as follows:
CodeSwitchover = |(CodeNewTarget – CodePreviousTarget)| / 2 , (4)
and
T1 = CodeSwitchover × tdT1 ,
(5)
where tdT1 is the delay factor for the initial time subinterval, in
table 1.
The current amplitude at the switchover point is calculated based
on equation 1, as follows:
ISwitchover = (CodeLow + CodeSwitchover ) × 100 μA ,
(6)
where CodeLow is the lesser of CodeNewTarget and CodePreviousTarget.
The time interval from the switchover point, T1, until the target
current level is reached, T2, is calculated as follows:
T2–T1 = CodeSwitchover × tdT2 ,
(7)
where tdT2 is the delay factor for the second time subinterval, in
table 1.
Output Function Programming
Two examples of output level and slew rate programming are
shown in figure 1. Both examples are ramp slew rate functions,
using the dual-subinterval method. In example A, an increment in
IOUT is shown, and example B shows a decrement in IOUT.
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
5
5 Page 
A3907
Low Voltage Voice Coil Motor Driver
Copyright ©2009-2013, Allegro MicroSystems, LLC
Allegro MicroSystems, LLC reserves the right to make, from time to time, such departures from the detail specifications as may be required to
permit improvements in the performance, reliability, or manufacturability of its products. Before placing an order, the user is cautioned to verify that
the information being relied upon is current.
Allegro’s products are not to be used in any devices or systems, including but not limited to life support devices or systems, in which a failure of
Allegro’s product can reasonably be expected to cause bodily harm.
The information included herein is believed to be accurate and reliable. However, Allegro MicroSystems, LLC assumes no responsibility for its
use; nor for any infringement of patents or other rights of third parties which may result from its use.
For the latest version of this document, visit our website:
www.allegromicro.com
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
11
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| Páginas | Total 11 Páginas | |
| PDF Descargar | [ Datasheet A3907.PDF ] | |
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