DRV120 Datasheet, PDF (7/16 Pages) Texas Instruments – POWER SAVING CURRENT CONTROLLED SOLENOID DRIVER

DRV120
www.ti.com
SLVSBG3A – JUNE 2012 – REVISED AUGUST 2012
FUNCTIONAL DESCRIPTION
DRV120 controls the current through the solenoid as shown in Figure 3. Activation starts when EN pin voltage is
pulled high either by an external driver or internal pull-up. In the beginning of activation, DRV120 allows the load
current to ramp up to the peak value I_PEAK and it regulates it at the peak value for the time, t_KEEP, before reducing
it to I_HOLD. The load current is regulated at the hold value as long as the EN pin is kept high. The initial current
ramp-up time depends on the inductance and resistance of the solenoid. Once EN pin is driven to GND, DRV120
allows the solenoid current to decay to zero.
I_SOLENOID
I_PEAK
I_HOLD
t
t_KEEP
EN
t
Figure 3. Typical Current Waveform Through the Solenoid
t_KEEP is set externally by connecting a capacitor to the KEEP pin. A constant current is sourced from the KEEP
pin that is driven into an external capacitor resulting in a linear voltage ramp. When the KEEP pin voltage
reaches 75 mV, the current regulation reference voltage, V_REF, is switched from V_PEAK to V_HOLD. Dependency of
t_KEEP from the external capacitor size can be calculated by:
t_KEEP
éësùû
=
C_KEEP
éëFùû
×
75
× 10³
ésù
êë_F úû
(1)
The current control loop regulates, cycle-by-cycle, the solenoid current by using an internal current sensing
resistor and MOSFET switch. During the ON-cycle, current flows from OUT pin to GND pin through the internal
switch as long as voltage over current sensing resistor is less than V_REF. As soon as the current sensing voltage
is above V_REF, the internal switch is immediately turned off until the next ON-cycle is triggered by the internal
PWM clock signal. In the beginning of each ON-cycle, the internal switch is turned on and stays on for at least
the time determined by the minimum PWM signal duty cycle, D_MIN.
I_PEAK and I_HOLD depend on fixed resistance values R_PEAK and R_HOLD as shown in Figure 4. If the PEAK pin is
connected to ground or if R_PEAK is below 33.33 kΩ (typ value), then I_PEAK is at its default value (internal setting).
The I_PEAK value can alternatively be set by connecting an external resistor to ground from the PEAK pin. For
example, if a 50-kΩ (= R_PEAK) resistor is connected between PEAK and GND, then the externally set I_PEAK level
will be 250 mA. If R_PEAK = 200 kΩ is, then the externally set I_PEAK level will be 83 mA. HOLD current external
setting, I_HOLD, works in the same way, but current levels are 40% of the I_PEAK. External settings for I_PEAK and
I_HOLD are independent of each other. I_PEAK and I_HOLD values can be calculated by using the formula below.
250mA
I_PEAK = _RPEAK × 66.67kW;66.67kW < R_PEAK < 550kW
(2)
100mA
I _HOLD = _RHOLD × 66.67kW;66.67kW < R_HOLD < 250kW
(3)
Copyright © 2012, Texas Instruments Incorporated
Product Folder Links: DRV120
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