ST AN2791 Application note
AN2791
Application note
L9352B coil driver for ABS/ESP applications:
current regulated channel analysis
Introduction
This document describes a detailed analysis on the current regulated channels of the ST
coil driver L9352B. This intelligent quad-low side switch is typically used to drive inductive
loads such as on-off valves of the hydraulic modulator of ABS
(a)
/ESP
(b)
control unit.
a. Antilock Brake System (ABS).
b. Electronic Stability Program (ESP).
June 2008 Rev 1 1/18
www.st.com
Contents AN2791
Contents
1 L9352B overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2 Test bench layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3 Linearity relationship test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
4 Opening/closing time of the INLET valves versus duty-cycle of the
hold-phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
5 Virtual current control loop on the Q1, Q2 channels of L9352B . . . . . 13
6 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2/18
AN2791 List of tables
List of tables
Table 1. INLET valve opening/closing time versus duty-cycle strategy . . . . . . . . . . . . . . . . . . . . . . 12
Table 2. Results of the first operative condition under test. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Table 3. Results of the second operative condition under test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Table 4. Comparison between the current on loadsdrien by reg. channels and unreg.
channels before and after the VCCL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Table 5. Results of the last operative condition under test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Table 6. Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
3/18
List of figures AN2791
List of figures
Figure 1. L9352B application diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Figure 2. Comparison between the "ideal" linear relationship and the experimental data. . . . . . . . . . 6
Figure 3. Test bench layout used to characterize current control channels of L9352B. . . . . . . . . . . . 7
Figure 4. Current waveform produced on the load by the test coil energizing strategy . . . . . . . . . . . . 8
Figure 5. Comparison between the "ideal" linear relationship and the experimental data
for two different load conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Figure 6. Coil current driven by means of L9352B in a typical ABS mission profile: coils on valves . . 9
Figure 7. Coil current driven by means of L9352B in a typical ABS mission profile: stand-alone coils. 10
Figure 8. "Pull-in"- "hold" phase duty-cycle strategy traditionally adopted to drive on-off valves. . . . 11
Figure 9. Evaluation of the VCCL on the L9352B unregulated channels:
first test condition block scheme. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Figure 10. Evaluation of the VCCL on the L9352B unregulated channels:
last test condition block scheme. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
4/18
AN2791 L9352B overview
1 L9352B overview
The L9352B (see Figure 1) is designed to drive inductive loads (e.g. relays, electromagnetic
valves, etc.) in low side configuration. Integrated active Zener-clamp, for channels 1 and 2,
or free wheeling diodes, for channels 3 and 4, allow the recirculation of the current of the
inductive loads during the off-state of the DMOS.
All four channels are monitored with a status output. All wiring to the loads and supply pins
of the device are controlled.
The device is self-protected against short circuit at the outputs and over-temperature.
Channels 3 and 4 work as current regulator.
A PWM signal, with a 2 kHz frequency, on the input defines the target for the output current,
in particular, there is a linear relationship between the duty-cycle of the PWM input signal
and the target value of the current (see Figure 2).
The current is measured during recirculation phase of the load, that is, during the off-state of
the DMOS. A sensing resistor, integrated in the IC and placed on the drain of the DMOS and
of the free-wheeling diode, is devoted to measure the current.
The benefit of the current regulation is an optimization of the PWM duty-cycle strategy
against changes in the load conditions (e.g. temperature gradient and as a consequence
coil resistor increases). Moreover, a test mode compares the differences between the two
regulators. This "drift" test compares the output PWM of the regulators. Using this feature a
drift of the load during lifetime can be detected.
Figure 1. L9352B application diagram
5 V logic supply
EN
CLK
IN1
ST1
IN4
ST4
Microcontroller
IN2
ST2
IN3
ST3
TEST
VS VCC VDD
Overtemperature
Channel 4
LOGIC
LOGIC
Overtemperature
Channel 3
LOGIC
LOGIC
drift-det.
Internal Supply
Overtemperature
Channel 1
&
DA
Overtemperature
Channel 2
&
DA
Open Load
Overload
GND-det.
Open Load
Overload
GND-det.
Open Load
Overload
GND-det.
Open Load
Overload
GND-det.
Vbatt
Q1
Free wheeling valve
IPD
D4
Q4
Regulated valve
IPD
Q2
Free wheeling valve
IPD
D3
Q3
Regulated valve
IPD
GND
5/18
L9352B overview AN2791
Figure 2. Comparison between the "ideal" linear relationship and the experimental
data
6/18
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