Detailed Description
The MAX14874 relay/valve driver, which can also be used
as a DC brushed motor driver, provides a low-power and
flexible solution for driving and controlling loads with volt-
ages between 4.5V and 36V. Peak currents of up to 2.8A
ensure for large force/torque that is controllable by an
external PWM signal.
Charge-pump-less design ensures for minimal external
components and low supply current.
Shoot-through protection with a 140ns (typ) dead time
ensures low operating current. Internal free-wheeling
diodes absorb inductive motor currents. The FAULT output
signals thermal overload and overcurrents.
Overcurrent Protection
The MAX14874 is protected against shorts on M1/M2 to
V
DD
and between M1 and M2 via overcurrent limiting.
When a current above 6A (typ) flows through M1 or M2
for longer than 1µs, an overcurrent condition is detected
and the H-bridge drivers are automatically disabled and
the FAULT output asserts.
If the overcurrent condition continues for longer than the
overcurrent autoretry timeout (2ms, typ) the MAX14874
enters autoretry mode. In autoretry mode, the M1 and M2
outputs are re-enabled for 1µs (typ) and FAULT goes high
impedance. The drivers are disabled again and FAULT is
re-asserted if the overcurrent condition persists.
Short Circuit Protection
The M1 and M2 outputs are safe against all short circuits,
if the R
SENSE_
resistors on COM1 and/or COM2 have a
value of less than 50mΩ.
When using a larger sense resistor, protect the part
against shorts to GND by connecting a silicon diode (for
example MURA205T3) between the M_ driver output
and ground. These protection diodes are not needed
if the maximum operating supply voltage (V
DD
) is less
than 24V, and the sense resistor, R
SENSE_
, on COM_ is
100mΩ or less.
Driver Control
The IN_ input is used for motor speed/torque control.
Increasing or decreasing the duty cycle at IN_ sets the
effective (average) voltage across the motor terminals
and allows current control.
When IN_ is logic-high, the motor is driven high (see
Function Table). When IN_ is logic low, M_ pin is driven low.
MAX14874 4.5V to 36V Dual Relay/Valve/Motor Driver
www.maximintegrated.com
Maxim Integrated
│
9
Functional Diagram
* OPTIONAL DIODE. SEE THE SHORT-CIRCUIT PROTECTION SECTION FOR MORE INFORMATION.
VDD
VDDM1
M2
COM1
R
SENSE1
MCU
IN1
IN2
3.3V
3.3V
24V
24V
IRQ
COM2
MAX14874
ADC
A
FAULT
GND
EN1
EN2
DRIVER 1
DRIVER 2
24V
*
*
