TCA8418E_15 Datasheet, PDF (41/50 Pages) Texas Instruments – I2C Controlled Keypad Scan IC With Integrated ESD Protection

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9.2.3 Application Curves
4
4
3.5
3.5
3
3
2.5
2.5
2
2
1.5
1.5
1
1
0.5
0.5
ROW0
INT Output
0
0
-2
0
2
4
6
8
10
12
14
16
18
20
22
24
26
-40
Time (ms)
D001
Figure 34. Initial Key Press to Interrupt Output
TCA8418E
SCPS222C – MAY 2010 – REVISED OCTOBER 2015
ROW0
INT Output
-20
0
20
40
60
80
100
Time (µs)
D002
Figure 35. Zoom On Second Scan
10 Power Supply Recommendations
In the event of a glitch or data corruption, TCA8418E can be reset to its default conditions by using the power-on
reset feature. Power-on reset requires that the device go through a power cycle to be completely reset. This
reset also happens when the device is powered on for the first time in an application.
The two types of power-on reset are shown in Figure 36 and Figure 37.
V_CC
Ramp-Up
Ramp-Down
Re-Ramp-Up
V_{CC_TRR_GND}
V_{CC_RT}
V_{CC_FT}
Time to Re-Ramp
V_{CC_RT}
Time
Figure 36. V_CC is Lowered Below 0.2 V or 0 V and Then Ramped Up to V_CC
V_CC
Ramp-Down
V_IN drops below POR levels
V_{CC_TRR_VPOR50}
Ramp-Up
V_{CC_FT}
Time to Re-Ramp
V_{CC_RT}
Time
Figure 37. V_CC is Lowered Below the POR Threshold, Then Ramped Back Up to V_CC
Table 28 specifies the performance of the power-on reset feature for TCA8418E for both types of power-on reset.
V_{CC_FT}
V_{CC_RT}
V_{CC_TRR_GND}
V_{CC_TRR_POR50}
Table 28. Recommended Supply Sequencing and Ramp Rates⁽¹⁾
PARAMETER
Fall rate
Rise rate
Time to re-ramp (when V_CC drops to GND)
Time to re-ramp (when V_CC drops to V_{POR_MIN} – 50 mV)
See Figure 36
See Figure 36
See Figure 36
See Figure 37
MIN TYP
1
0.01
0.001
0.001
MAX
100
100
UNIT
ms
ms
ms
ms
(1) T_A = –40°C to 85°C (unless otherwise noted)
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