A3918
Low Voltage DC Motor Driver
Features and Benefits
▪
2.5 to 9 V operation
▪
Internal PWM current control
▪
Synchronous rectification for reduced power dissipation
▪
Peak current output flag
▪
Undervoltage lockout
▪
Low R
DS(on)
outputs
▪
Small package
▪
Brake mode for DC motor
▪
Sleep function
▪
Crossover-current protection
▪
Thermal shutdown
Description
Designed for pulse width modulated (PWM) control of a low
voltage DC motor, the A3918 is capable of output currents up
to 1.5 A and operating voltages from 2.5 to 9 V.
The A3918 has an internal fixed off-time PWM timer that
sets a peak current based on the selection of a current sense
resistor. An overcurrent output flag is provided that notifies
the user when the current in the motor winding reaches the
peak current determined by the sense resistor. The fault output
does not affect driver operation.
The A3918 is provided in a 16-contact, 3 mm × 3 mm, 0.75 mm
nominal overall height QFN, with exposed pad for enhanced
thermal dissipation. It is lead (Pb) free, with 100% matte tin
leadframe plating.
Applications include the following:
▪
Digital still cameras (DSC)
▪
Cell phone cameras
▪
USB powered devices
▪
Battery powered devices
Package: 16-contact QFN (suffix ES)
3 × 3 mm
0.75 mm overall height
Approximate size
Functional Block Diagram
0.1
μF
0.1
μF
VCP
CP2
CP4
CP1
CP3
0.1
μF
VBB
Charge
Pump
+5 V
Regulator
SLEEP
Sense
FL
10
μF
10 V
IN1
Control Logic
IN2
Sense
PWM Latch
and
Blanking
Comparator
Bridge
VCP
VBB
OUTA
OUTB
SENSE
R
SENSE
GND
PAD
GND
GND
A3918-DS
A3918
Selection Guide
Part Number
A3918SESTR-T
Low Voltage DC Motor Driver
Packing
1500 pieces per 7-in. reel
Package
16-pin QFN with exposed thermal pad
Absolute Maximum Ratings
Characteristic
Load Supply Voltage
Logic Input Voltage Range
Sense Voltage
Symbol
V
BB
V
IN
V
SENSE
Continuous
Pulsed, t
w
< 1
μs
May be limited by duty cycle, ambient
temperature, and heat sinking. Under
any set of conditions, do not exceed
the specified current rating or a junction
temperature of 150°C.
Range S
Continuous
Peak, DC < 30%
Notes
Rating
9.6
–0.3 to 7
0.5
1
1
1.5
–20 to 85
150
–40 to 150
Units
V
V
V
V
A
A
°C
°C
°C
Output Current
I
OUT
Operating Temperature Range
Junction Temperature
Storage Temperature Range
T
A
T
J(max)
T
stg
Thermal Characteristics
may require derating at maximum conditions, see application information
Characteristic
Package Thermal Resistance
Symbol
R
θJA
Test Conditions*
4-layer PCB based on JEDEC standard
Value Units
42
ºC/W
*Additional thermal information available on the Allegro website.
Terminal List Table
Name
Number
15
1
14
16
7
2, 6, 8
4
5
12
10
–
11
3
9
13
Function
Charge pump capacitor terminal 1
Charge pump capacitor terminal 2
Charge pump capacitor terminal 3
Charge pump capacitor terminal 4
Current limit flag
Ground
Control input 1
Control input 2
DMOS full-bridge output A
DMOS full-bridge output B
Exposed thermal pad
Current sense resistor terminal
Sleep logic input, active low
Supply Voltage
Reservoir capacitor terminal
Pin-out Diagram
VCP
CP4
CP1
CP3
CP1
CP2
CP3
CP4
FL
GND
IN1
IN2
OUTA
OUTB
PAD
SENSE
¯ ¯¯ ¯ ¯
¯¯ ¯ ¯ ¯
SLEEP
VBB
VCP
16
15
14
CP2
GND
SLEEP
IN1
1
2
3
4
5
6
7
8
PAD
13
12 OUTA
11
SENSE
10 OUTB
9
VBB
GND
IN2
GND
FL
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
2
A3918
Low Voltage DC Motor Driver
ELECTRICAL CHARACTERISTICS
1,2
valid at T
A
= 25°C and V
BB
= 2.5 to 9 V, unless otherwise noted
Characteristics
Operating Voltage Range
VBB Supply Current
Symbol
V
BB
Test Conditions
I
OUT
= 0 mA, PWM = 50 kHz, Duty Cycle = 50%
Min.
2.5
–
–
–
–
–
–
–
160
–
–20
2.0
–
Typ.
–
5
3
150
0.52
0.78
0.62
0.93
200
–
–
–
–
<100
<–100
150
–
–
–
–
300
3
30
235
100
425
2.31
300
165
15
Max.
9
–
–
500
0.60
–
0.74
–
240
1
20
5.5
0.8
500
–500
–
0.4
–
200
1
–
3.9
–
350
200
650
2.45
400
–
–
Units
V
mA
mA
nA
Ω
Ω
Ω
Ω
mV
V
μA
V
V
nA
nA
mV
V
V
mV
μA
μs
μs
μs
ns
ns
ns
V
mV
°C
°C
I
BB
I
OUT
= 0 mA, outputs disabled, V
BB
= 9.6 V
Sleep mode, V
IN
< 0.4 V
Source driver, I
OUT
= 400 mA , V
BB
= 3 V, T
J
= 25°C
Source driver, I
OUT
= 400 mA , V
BB
= 3 V, T
J
= 85°C
Sink driver, I
OUT
= 400 mA, V
BB
= 3 V, T
J
= 25°C
Sink driver, I
OUT
= 400 mA, V
BB
= 3 V, T
J
= 85°C
FL falling edge
I = 400 mA
Outputs, V
OUT
= 9 V
Output Resistance
R
DS(on)
Current Trip Sense Voltage
Clamp Diode Voltage
Output Leakage Current
Control Logic
Logic Input Voltage
Logic Input Current
Input Hysteresis
¯ ¯¯ ¯ ¯ Input
¯¯ ¯ ¯ ¯
SLEEP
Fault Output
Fault Output Leakage Current
Fault Output Timer
Blank Time
Fixed Off-Time
Propagation Delay Time
Protection Circuitry
Crossover Delay
VBB Undervoltage Lockout Threshold
VBB Undervoltage Lockout Hysteresis
Thermal Shutdown Temperature
Thermal Shutdown Hysteresis
1
For
2
Specifications
V
SENSE
V
f
I
DSS
V
IN(1)
V
IN(0)
I
IN(1)
I
IN(0)
V
INhys
V
SLEEP(0)
V
SLEEP(1)
V
FL
I
FL
t
FL
t
BLANK
t
OFF
t
pd(on)
t
pd(off)
t
COD
V
BBUVLO
V
BBUVHYS
T
JTSD
T
JTSDHYS
V
IN
= 5.5 V
V
IN
= 0.8 V
–
–
–
–
2
Flag asserted, I
FL
= 1 mA
V
FL
= 5 V
Reset of PWM latch
–
–
–
2.1
–
Input high to source on, input low to source off
Input low to sink off, input high to sink on
100
50
200
V
BB
rising
2.2
200
–
–
input and output current specifications, negative current is defined as coming out of (sourcing) the specified device pin.
over the operating temperature range are assured by design and characterization.
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
3
A3918
Low Voltage DC Motor Driver
Functional Description
Device Operation
The A3918 is a full-bridge low voltage
motor driver capable of operating one high current DC motor.
MOSFET output stages substantially reduce the voltage drop and
the power dissipation of the outputs of the A3918, compared to
typical drivers with bipolar transistors.
Output current can be regulated by pulse width modulating
(PWM) the inputs. In addition supporting external PWM of the
driver, the A3918 limits the peak current by internally PWMing
the source driver when the current in the winding exceeds the
peak current, which is determined by a sense resistor. A fault
output notifies the user that peak current was reached. If internal
current limiting is not needed, the sense pin should be shorted to
ground.
Internal circuit protection includes thermal shutdown with hyster-
esis, undervoltage lockout, internal clamp diodes, and crossover
current protection.
The A3918 is designed for portable applications, providing a
power-off low current sleep mode and an operating voltage of
2.5 to 9 V.
External PWM
Output current regulation can be achieved by
pulse width modulating the inputs. Slow decay mode is selected
by holding one input high while PWMing the other input. Hold-
ing one input low and PWMing the other input results in fast
decay. Refer to the Applications Information section for further
information.
Blanking
This function blanks the output of the current sense
comparator when the outputs are switched. The comparator
output is blanked to prevent false overcurrent detections due to
reverse recovery currents of the clamp diodes or to switching
transients related to the capacitance of the load. The blank time,
t
BLANK
, is approximately 3
μs.
Sleep Mode
An active-low control input used to minimize
power consumption when the A3918 is not in use. This dis-
ables much of the internal circuitry including the output drivers,
internal regulator, and charge pump. A logic high allows normal
operation. When coming out of sleep mode, wait 1.5 ms before
issuing a command, to allow the internal regulator and charge
pump to stabilize.
Enable
When all logic inputs are pulled to logic low, the outputs
of the bridges are disabled. The charge pump and internal cir-
cuitry continue to run when the outputs are disabled.
Charge Pump
(CP1, CP2, CP3, and CP4) When supply volt-
ages are lower than 3.5 V, the two-stage charge pump triples the
input voltage to a maximum of 7 V above the supply. The charge
pump is used to create a supply voltage greater than V
BB
, to drive
the source-side DMOS gates. For pumping purposes, a 0.1
μF
ceramic capacitor should be connected between CP1 and CP2,
and between CP3 and CP4. A 0.1 uF ceramic capacitor is required
between VCP and VBB, to act as a reservoir to operate the high-
side DMOS devices.
Thermal Shutdown
The A3918 will disable the outputs if the
junction temperature reaches 165°C. When the junction tempera-
ture drops 15°C, the outputs will be enabled.
Brake Mode
When driving DC motors, the A3918 goes into
brake mode (turns on both sink drivers) when both of its inputs
are high (IN1 and IN2). There is no protection during braking, so
care must be taken to ensure that the peak current during braking
does not exceed the absolute maximum current.
Internal PWM Current Control
The bridge is controlled
by a fixed off-time PWM current control circuit that limits the
load current to a desired value, I
TRIP
. Initially, a diagonal pair
of source and sink DMOS outputs are enabled and current flows
through the motor winding and the current sense resistor, R
SENSE
.
When the voltage across R
SENSE
equals the internal reference
voltage, the current sense comparator resets the PWM latch,
which turns off the source driver.
The maximum value of current limiting, I
TRIP
(max) , is set by the
selection of the sense resistor, R
SENSE
, and is approximated by a
transconductance function:
I
TRIP
(max) = 0.2 /
R
SENSE
.
It is critical to ensure the maximum rating on the SENSE pin
(0.5 V) is not exceeded.
Synchronous Rectification
When a PWM off-cycle is trig-
gered by an internal fixed off-time cycle, load current recirculates
in slow decay SR mode. During slow decay, current recirculates
through the sink-side FET and the sink-side body diode. The SR
feature enables the sink-side FET, effectively shorting out the
body diode. The sink driver is not enabled until the source driver
is turned off and the crossover delay has expired. This feature
helps lower the voltage drop during current recirculation, lower-
ing power dissipation in the bridge.
Overcurrent Output Flag
When the peak current (set by the
external resistor) is reached, the fault pin, FL, is pulled low.
When a reset of the PWM latch occurs, the fault timer begins. At
each PWM latch reset, the timer is reset to zero. After approxi-
mately 300
μs,
if no peak current event was triggered, the timer
expires and the fault is released. This ensures that during PWM
current limiting, the fault pin remains in a fault state.
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
5
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