Atmel ATA6264 - Manual (Page 11)

11
4929B–AUTO–01/07
ATA6264 [Preliminary]
5.1 Discharger Circuit
Applications using the ATA6264 usually use a reverse polarity protection diode (D1 in Figure
5-1 ) in the power supply to prevent any damage if the wrong polarity is applied to V
K30
. Unfortu-
nately, this method includes some risk as can be seen in the following description:
During Standby mode (V
K15
< 3V and KEYLATCH = OFF) the IC consumes only a low current,
I
K30
. Any peaks on the supply voltage (V
Pulse
in Figure 5-1 ) will gradually charge the blocking
capacitor (C1). D1 prevents the capacitor from being discharged via the power supply and the
very small quiescent current via the IC can also be neglected. This means that during long peri-
ods of Standby mode, the IC’s supply voltage could increase continuously until finally the
maximum supply voltage limit would be exceeded and the IC could be damaged. ATA6264
therefore features a discharger circuit which avoids such unwanted effects. If V
K30
exceeds a
threshold value of approximately 26.8V, the blocking capacitor is discharged via an integrated
resistor until V
K30
again falls below the threshold.
Figure 5-1. Discharger Circuit
5.2 Initial Programming of the ATA6264
The ATA6264 supports different output voltages at the VSAT, VPERI and the VCORE regula-
tors. In addition, different modes at the ISO9141 interfaces can be adjusted at the initial
programming (IP). The memory cells are one-time programmable (OTP) and cannot be changed
after the IP (default values are “0”). In general, the IP is done after mounting the ATA6264 on the
PCB with an in-circuit tester. The programming voltage of 11.7V has to be applied on pin VSAT.
It is also possible to use the VSAT regulator as the programming voltage because VSAT is pro-
grammed to 11.7V (±0.5V) as long as the Test mode is entered and the lock bit is not set. To
ensure proper programming of the ATA6264, at least a 10-µF electrolytic cap and a 100-nF
ceramic cap have to be applied at pin VSAT.
V
Pulse
V
Batt
26.8V
K30
D1
C1 8 k Ω