FDS 6531/6532 005
Data Sheet 71M6531D/F-71M6532D/F
3.11 Connecting the Reset Pin
Even though a functional meter will not necessarily need a reset switch, it is useful to have a reset push-
button for prototyping as shown in Figure 38, left side. The RESET signal may be sourced from V3P3SYS
(functional in MISSION mode only), V3P3D (MISSION and BROWNOUT modes), or VBAT (all modes, if
a battery is present), or from a combination of these sources, depending on the application.
For a production meter, the RESET pin should be protected by the by the external components shown in
Figure 38, right side. R1 should be in the range of 100 Ω and mounted as closely as possible to the IC.
VBAT/
V3P3D
V3P3D
71M6533
71M6532D/F
71M6531D/F
71M6531D/F
71M6532D/F
R2
1kΩ
Reset
Switch
RESET
RESET
GNDD
100Ω
R1
10kΩ
R1
0.1µF
DGND
Figure 38: External Components for the RESET Pin: Push-button (Left), Production Circuit (Right)
Since the 71M6531 generates its own power-on reset, a reset button or circuitry, as shown in Figure 38,
is only required for test units and prototypes.
3.12 Connecting the Emulator Port Pins
Even when the emulator is not used, small shunt capacitors to ground (22 pF) should be used for protection
from EMI as illustrated in Figure 39. Production boards should have the ICE_E pin connected to ground.
LCD Segments
(optional)
V3P3D
ICE_E
62 Ω
E_RST
62 Ω
E_RXT
E_TCLK
62 Ω
71M6531D/F
71M6532D/F
22 pF 22 pF 22 pF
Figure 39: External Components for the Emulator Interface
3.13 Connecting a Battery
It is important that a valid voltage is connected to the VBAT pin at all times. For meters without a battery,
VBAT should be connected directly to V3P3SYS. Designs for meters with batteries need to ensure that
the meter functions even when the battery voltage decreases below the specified voltage for VBAT. This
can be achieved by connecting a diode from V3P3SYS to VBAT. However, the battery test will yield
inaccurate results if that technique is used, since the voltage at V3P3SYS will feed current to the VBAT
pin. A better solution is shown in Figure 40: During the battery test, a DIO pin is activated as an output
and applies a low voltage to the anode of the diode. This prevents the voltage at the power supply to in-
fluence the voltage at the VBAT pin.
v1.3
© 2005-2010 TERIDIAN Semiconductor Corporation
69
TERIDIAN [ TERIDIAN SEMICONDUCTOR CORPORATION ]
