U2640B Datasheet, PDF (3/10 Pages) ATMEL Corporation – Intemittent- and Wipe/ Wash Control for Wiper Systems

U2640B
Intermittent and Wipe/Wash Mode
The wipe/wash function has priority over the interval
function. If switch WIWA is closed during the interval
function, wipe/wash mode is activated immediately after
the debounce time, t_D, even if an on-delay is programmed
(t_DEL = 0 s). Expiry of t_AW is directly followed by the next
relay on-time, t_ON, of intermittent mode.
Oscillator
All timing sequences are derived from an RC-oscillator
whose charging time, t₁, is determined by an external
resistor, R_OSC, and whose discharging time, t_2, is
determinated by an integrated 2-kW resistor. Since
tolerance and temperature response of the integrated
resistor are far higher than those of the external resistor,
t₁/t₂ must be selected to be greater than 20 for stability
reasons. The minimum value of R_OSC should not be less
than 68 kW.
Calculating cycle duration and frequency:
t = t₁ + t₂ = C_OSC ( 0.74 R_OSC + 2260 W)
and f_OSC = 1/t
Calculating the capacitor for a given resistor:
C_OSC = t / ( 0.74 R_OSC + 2260 W)
Calculating the oscillator resistance for a given capacitor:
R_OSC = 1.34 ( t / C_OSC – 2260 W)
Recommended frequency: f_OSC = 200 Hz
(for R_OSC = 200 kW, C_OSC = 33 nF)
All times can be varied jointly within specific limits by
varying the oscillator frequency (see table 1). The oscilla-
tor is operable up to 50 Hz.
Power Supply
For reasons related to protection against interference and
destruction, the Pin V_S must be provided with an RC net-
work for limiting the current in the event of overvoltage
and for buffering in the event of voltage drops.
Proposed ratings: R_V = 510 W, C_V = 47 mF. An integrated
14-V Zener diode is connected between V_S and GND.
Interference Voltages and Load-Dump
In the case of transients, the integrated Zener diode limits
the voltage of the relay output to approximately 28 V. In
the case of load-dump, a current (dependent upon R_V and
C_V) flows through the integrated 14-V Zener diode, and
the relay output is switched on at V_Batt > 30 V in order to
avoid destruction of the output. The output transistor is
rated such that it can withstand the current generated dur-
ing the load-dump through the relay coil. In practice, the
windscreen wiper motor is switched on via the relay and
thus the amplitude of the load-dump pulse is limited. The
supply voltage of the circuit is limited to 14 V by the inte-
grated Zener diode, and the inputs are protected by
external protective resistors and integrated Zener diodes.
RF suppression is implemented with a low-pass filter at
the inputs, consisting of a protective resistor and the inte-
grated capacitor.
Power-on Reset (POR)
When the supply voltage is applied, a power-on reset
pulse is generated which sets the circuit’s logic to a
defined initial state. The POR threshold is approximately
V_S = 4.3 V.
Table 1 Change in times by varying the oscillator frquency
f_{osc (Hz)}
100
120
140
160
180
200
220
240
260
280
300
400
t_D [ms]
140
116
100
87
77
70
64
58
54
50
46
35
t_DL [ms]
35
29
25
22
19
17
16
14
13
12
11
9
t_ON [ms]
960
800
686
600
533
480
436
400
370
343
320
240
t_INT [s]
11.84
9.68
8.45
7.40
6.57
5.92
5.38
4.93
4.55
4.23
3.95
2.96
t_AW [s]
10.24
8.53
7.31
6.40
5.68
5.12
4.65
4.26
3.94
3.66
3.41
2.56
t_DEL [s]
920
766
657
575
511
460
418
383
353
328
306
230
Rev. A4, 03-Apr-01
3 (10)