71M6521 Demo Board User’s Manual
Revision 2.18
© 2005-2009 TERIDIAN Semiconductor Corporation
Page: 75 of 111
3.3 CHANGES TO THE D6521T4A7
The Demo Board revision 7.0 (D6521T4A7) improves performance over previous revisions in the following
areas:
1. Optimized schematics for increased resistance against ESD.
2. Optimized layout for improved accuracy at low currents.
3. Added ICE_E signal to headers J14 and J15.
4. Default configuration is for resistive shunt.
The changes made to the D6521T4A7 design will be described in the following four chapters.
3.3.1 INCREASED ESD PROTECTION
The following components were added or removed to improve the stability of the V3P3D net for increased
rejection of ESD, as specified by IEC 6100-4-2 (ESD spikes applied to table-top equipment via a metallic
plate mounted underneath the meter):
C38 (1,000pF) added at J2
C44 (1,000pF) added at J14
C45 (1,000pF) added at J12
C46 (1,000pF) added at JP12
C47 (1,000pF) added at JP5
Pull-up resistors R88, R89, R119 removed at J14
C7, C13, C48 (22pF) added at J14
3.3.2 IMPROVED ACCURACY AT LOW CURRENTS
Improvement of meter accuracy at low currents was achieved by assigning both copper structures at the
current inputs (top and bottom) to the V3P3 net, as shown in Figure 3-2.
Figure 3-2: Top (Left) and Bottom Copper (Right) Structures at Current Inputs
3.3.3 ACCESS TO THE ICE_E SIGNAL
Another improvement is the added access to the ICE_E signal via the filter formed by R100 (1k
Ω
) and C12
(1,000pF) for the TFP-2 Flash Programming Device at the programming headers J 15 (pin #6) and J14 (pin
#2). These pins allow the TFP-2 to reset the 71M6521 chip after a flash erase operation using the watchdog-
timeout mechanism, allowing flash memory parts with the
SECURE
bit set (see the data sheet for more
information) to be erased and reprogrammed.
3.3.4 DEFAULT CONFIGURATION FOR RESISTIVE CURRENT SHUNT
Due to the majority of the 71M6521 meter designs using resistive shunts, the D6521T4A7 Demo Board are
shipped configured for shunts. To convert the D6521T4A7 Demo Board to CT configuration, the following
changes have to be made:
1. Remove R88
2. Install L12, L9, R19, and C10
3. Remove R24 and install the proper burden resistor combination at R24 and R25.
V3P3
V3P3
V3P3
V3P3
V3P3 star
point
GND star
point
