AD8436-EVALZ Analog Devices, AD8436-EVALZ Datasheet - Page 13

• Manufacturer Part Number: AD8436-EVALZ
• Description: Power Management IC Development Tools Eval Board
• Manufacturer: Analog Devices
• Type: Other Power Managementr
• Series: AD8436r

Specifications of AD8436-EVALZ

• Rohs: yes
• Product: Evaluation Boards
• Tool Is For Evaluation Of: AD8436
• Input Voltage: + / - 18 V
• Maximum Operating Temperature: + 125 C
• Minimum Operating Temperature: - 40 C
• Factory Pack Quantity: 1

Data Sheet
For simplicity, Figure 29 shows ripple vs. frequency for four
combinations of CAVG and CLPF
Figure 30 shows the effects of averaging and post-rms filter
capacitors on transition and settling times using a 10-cycle,
50 Hz, 1 second period burst signal input to demonstrate time-
domain behavior. In this instance, the averaging capacitor value
was 10 µF, yielding a ripple value of 6 mV rms. A postconversion
capacitor (CLPF) of 0.68 μF reduced the ripple to 1 mV rms. An
averaging capacitor value of 82 μF reduced the ripple to 1 mV
but extended the transition time (and cost) significantly.
CAVG Capacitor Styles
When selecting a capacitor style for CAVG there are certain
tradeoffs.
For general usage, such as most DMM or power measurement
applications where input amplitudes are typically greater than
1 mV, surface mount tantalums are the best overall choice for
space, performance, and economy.
For input amplitudes less than around a millivolt, low dc leakage
capacitors, such as film or X8L MLCs, maintain rms conversion
accuracy. Metalized polyester or similar film styles are best, as
long as the temperature range is appropriate. X8L grade MLCs are
rated for high temperatures (125°C or 150°C), but are available only
up to 10 μF. Never use electrolytic capacitors, or X7R or lower grade
ceramics.
Figure 29. Residual Ripple Voltage for Various Filter Configurations
Figure 30. Effects of Various Filter Options on Transition Times
0.0001
0.001
0.01
0.1
1
10
INPUT
50Hz 10 CYCLE BURST
400mv/DIV
CAVG = 10µF FOR BOTH PLOTS,
BUT RED PLOT HAS NO LOW-PASS FILTER,
GREEN PLOT HAS CLPF = 0.68µF
10mV/DIV
TIME (100ms/DIV)
INPUT FREQUENCY (Hz)
AC INPUT = 300mV rms
100
CAVG = 1µF, CLPF = 0.33µF
CAVG = 1µF, CLPF = 3.3µF
CAVG = 10µF, CLPF = 0.33µF
CAVG = 10µF, CLPF = 3.3µF
CAVG = 82µF
1k
Rev. B | Page 13 of 24
Basic Core Connections
Many applications require only a single external capacitor for
averaging. A 10 µF capacitor is more than adequate for acceptable
rms errors at line frequencies and below.
The signal source sees the input 8 kΩ voltage-to-current conversion
resistor at Pin RMS; thus, the ideal source impedance is a
voltage source (0 Ω source impedance). If a non-zero signal source
impedance cannot be avoided, be sure to account for any series
connected voltage drop.
An input coupling capacitor must be used to realize the near-zero
output offset voltage feature of the AD8436. Select a coupling
capacitor value that is appropriate for the lowest expected
operating frequency of interest. As a rule of thumb, the input
coupling capacitor can be the same as or half the value of the
averaging capacitor because the time constants are similar. For
a 10 μF averaging capacitor, a 4.7 μF or 10 μF tantalum capacitor
is a good choice (see Figure 31).
Using a Capacitor for High Crest Factor Applications
The
factor errors. Crest factor is often overlooked when considering
the requirements of rms-to-dc converters, but it is very
important when working with signals with spikes or high peaks.
The crest factor is defined as the ratio of peak voltage to rms.
See Table 5 for crest factors for some common waveforms.
Crest factor performance is mostly applicable for unexpected
waveforms such as switching transients in switchmode power
supplies. In such applications, most of the energy is in these
peaks and can be destructive to the circuitry involved, although
the average ac value can be quite low.
AD8436
Figure 32. Connection for Additional Crest Factor Performance
*FOR POLARIZED CAPACITOR STYLES.
*FOR POLARIZED CAPACITOR STYLES.
contains a unique feature to reduce large crest
OR 10µF
OR 10µF
4.7µF
4.7µF
Figure 31. Basic Applications Circuit
+*
+*
2
2
RMS
RMS
CAVG
CAVG
IGND
IGND
19
11
19
11
CAVG
10µF
CAVG
AD8436
AD8436
10µF
+*
VEE
CCF
VEE
–5V
–5V
+*
10
18
10
0.1µF
CCF
OGND
OGND
VCC
VCC
+5V
+5V
17
17
8
8
OUT
OUT
9
9
AD8436