
TABLE 1. Recommended Output Filter Capacitors
C
O (F)
Voltage (V), R
ESR (m)
Make
Manufacturer
Part Number
Case Size
22
6.3, < 5
Ceramic, X5R
TDK
C3216X5R0J226M
1206
47
6.3, < 5
Ceramic, X5R
TDK
C3216X5R0J476M
1206
47
6.3, < 5
Ceramic, X5R
TDK
C3225X5R0J476M
1210
47
10.0, < 5
Ceramic, X5R
TDK
C3225X5R1A476M
1210
100
6.3, < 5
Ceramic, X5R
TDK
C3225X5R0J107M
1210
100
6.3, 50
Tantalum
AVX
TPSD157M006#0050
D, 7.5 x 4.3 x 2.9 mm
100
6.3, 25
Organic Polymer
Sanyo
6TPE100MPB2
B2, 3.5 x 2.8 x 1.9 mm
150
6.3, 18
Organic Polymer
Sanyo
6TPE150MIC2
C2, 6.0 x 3.2 x 1.8 mm
330
6.3, 18
Organic Polymer
Sanyo
6TPE330MIL
D3L, 7.3 x 4.3 x 2.8 mm
470
6.3, 23
Niobium Oxide
AVX
NOME37M006#0023
E, 7.3 x 4.3 x 4.1 mm
Output Voltage Setting
A resistor divider network from V
OUT to the FB pin determines
the desired output voltage as follows:
R
fbt is defined based on the voltage loop requirements and
R
fbb is then selected for the desired output voltage. Resistors
are normally selected as 0.5% or 1% tolerance. Higher accu-
racy resistors such as 0.1% are also available.
The feedback voltage (at V
OUT = 2.5V) is accurate to within
-2.5% / +2.5% over temperature and over line and load reg-
ulation. Additionally, the LMZ10505EXT contains error nulling
circuitry to substantially eliminate the feedback voltage vari-
ation over temperature as well as the long term aging effects
of the internal amplifiers. In addition the zero nulling circuit
dramatically reduces the 1/f noise of the bandgap amplifier
and reference. The manifestation of this circuit action is that
the duty cycle will have two slightly different but distinct op-
erating points, each evident every other switching cycle.
Loop Compensation
The LMZ10505EXT preserves flexibility by integrating the
control components around the internal error amplifier while
utilizing three small external compensation components from
V
OUT to FB. An integrated type II (two pole, one zero) voltage-
mode compensation network is featured. To ensure stability,
an external resistor and small value capacitor can be added
across the upper feedback resistor as a pole-zero pair to
complete a type III (three pole, two zero) compensation net-
work. The compensation components recommended in
Table2 provide type III compensation at an optimal control loop
performance. The typical phase margin is 45° with a band-
width of 80 kHz. Calculated output capacitance values not
listed in
Table 2 should be verified before designing into pro-
duction. A detailed application note is available to provide
verification support, AN-2013. In general, calculated output
capacitance values below the suggested value will have re-
duced phase margin and higher control loop bandwidth. Out-
put capacitance values above the suggested values will
experience a lower bandwidth and increased phase margin.
Higher bandwidth is associated with faster system response
to sudden changes such as load transients. Phase margin
changes the characteristics of the response. Lower phase
margin is associated with underdamped ringing and higher
phase margin is associated with overdamped response. Los-
ing all phase margin will cause the system to be unstable; an
optimized area of operation is 30° to 60° of phase margin, with
a bandwidth of 100 kHz ±20 kHz.
30118308
TABLE 2. LMZ10505EXT Compensation Component
Values
V
IN
(V)
C
O (F)
ESR (m
)
R
fbt
(k
)
C
comp
(pF)
R
comp
(k
)
Min
Max
5.0
22
2
20
200
27
1.5
47
2
20
124
56
1.4
100
1
10
82.5
120
1
150
1
5
63.4
180
1.21
150
10
25
63.4
220
16.5
150
26
50
44.2
220
23.7
220
15
30
63.4
220
23.7
220
31
60
76.8
220
57.6
3.3
22
2
20
118
39
9.09
47
2
20
76.8
82
8.45
100
1
10
49.9
180
4.12
150
1
5
40.2
330
2.0
150
10
25
43.2
330
11.5
150
26
50
49.9
270
25.5
220
15
30
40.2
390
15.4
220
31
60
48.7
330
35.7
Note: In the special case where the output voltage is 0.8V, it is recom-
mended to remove R
fbb and keep Rfbt, Rcomp, and Ccomp for a type III
compensation.
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LMZ10505EXT