DRV120_15 Datasheet, PDF (8/23 Pages) Texas Instruments – Power-Saving Current Controlled Solenoid Driver

DRV120
SLVSBG3B – JUNE 2012 – REVISED JULY 2015
Feature Description (continued)
I_SOLENOID
I_PEAK
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I_HOLD
t
t_KEEP
EN
t
Figure 2. 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 across the 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 approximately as shown in Figure 3. If the
PEAK pin is connected to ground or if R_PEAK or R_HOLD is below 33.33 kΩ (typical value), then I_PEAK is at its default
value (internal setting) of 200 mA for I_PEAK and 50 mA for I_HOLD. 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. In the 8-pin package, I_HOLD is set to 50 mA by default. In the 14-pin
package, external settings of I_HOLD works in the same way as I_PEAK. External settings for I_PEAK and I_HOLD are
independent of each other. Approximate I_PEAK and I_HOLD values can be calculated by using Equation 2 and
Equation 3.
250mA
I_PEAK = _RPEAK × 66.67kW;66.67kW < R_PEAK < 550kW
(2)
100mA
I _HOLD = _RHOLD × 66.67kW;66.67kW < R_HOLD < 250kW
(3)
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