5) Setup of bandwidth and velocity scaling for the optimized crit-
ically damped case should proceed as follows:
Note: Use of the -5 V inverter is not recommended for appli-
cations that require the highest BW and Tracking Rates.
- Select the desired f BW (closed loop) based on overall
system dynamicsꢀ
HIGHER TRACKING RATES AND CARRIER
FREQUENCIES.
- Select f
≥ 3ꢀ5f BW
carrier
Maximum tracking rate is limited by the velocity voltage satura-
tion (nominally 4 V) and the maximum internal clock rate (nomi-
nally 1,333,333 Hz for R CLK = 30k)ꢀ To achieve higher tracking
- Select the applications tracking rate (in accordance with TABLE 3),
and use appropriate values for R SET and R CLK
Full Scale Velocity Voltage
- Compute Rv =
resolution
Tracking Rate (rps) x .
x 50 pF x 1ꢀ.5 V
TABLE 3. MAX TRACKING RATE (MIN) IN RPS
3ꢀ. x Fs (Hz) x 108
- Compute CBW (pF) =
RESOLUTION
R SET
(Ω)
R CLK
(Ω)
Rv x (f BW).
10
12 14 16
115. .88 7. 18
17.8 43. 108 .7
30k** or open
30k
.0k
15k
- Where Fs = 67 kHz for R CLK = 30 KΩ
100 kHz for R CLK = .0 KΩ
.3k
.3k
1.5 kHz for R CLK = 15 KΩ
.304 576
*
*
0ꢀ9
CBW x f BW
- Compute RB =
TABLE 4. CARRIER FREQUENCY (MAX)
IN KHZ
CBW
- Compute
10
RESOLUTION
R SET
R CLK
(Ω)
(Ω)
10
10
10
10
10
12
10
10
10
10
14
7
16
30k** or open
30k
30k
.0k
15k
5
7
As an example:
.3k
.3k
.3k
10
10
*
10
*
Calculate component values for a 16 bit converter with 100Hz
bandwidth, a tracking rate of 10 RPS and a full scale velocity
of 4 Voltsꢀ
* Not recommendedꢀ
** The use of a high quality thin-film resistor will provide better temperature
stability than leaving openꢀ
4 V
- Rv =
= 97655 Ω
10 rps x .16 x 50 pF x 1ꢀ.5 V
3ꢀ. x 67 kHz x 108
- Compute CBW (pF) =
= .1955 pF
97655 x 100 Hz.
+5V
0ꢀ9
- Compute RB =
= 410 kΩ
.1955 x 10 -1. x 100 Hz
33
58
.7
VDD
VDD
VDDP
6) Using the -5V Inverter will eliminate the need for a -5 V sup-
plyꢀ Refer to FIGURE 5ꢀ for the necessary connectionsꢀ
.6
PCAP
+
RD-19.30
10 F/10V
When using the built-in -5 V inverter, the maximum tracking rate
should be scaled for a full-scale velocity output of 3ꢀ5 V maxꢀ
.4
NCAP
.3
16
VSSP
VSS
17
VSS
TABLE 2. TRACKING/BW RELATIONSHIP
47 F/10V
+
RPS (MAX)/BW
RESOLUTION
.5
..
GND
AGND
1
10
1.
14
16
0ꢀ50
0ꢀ.5
0ꢀ1.5
FIGURE 5. -5V INVERTER CONNECTIONS
5
ETC [ ETC ]
