LT1507
U
W U U
APPLICATIONS INFORMATION
move around, but at the same time phase moves with it so
that adequate phase margin is maintained over a very wide
range of ESR (≥ 5:1)
components. In many cases only CC is needed. Adding RC
willimprovephasemargin,butthismaynecessitatetheneed
for CF to limit switching frequency ripple at the VC pin.
80
200
150
100
50
In Figure 10, full loop phase/gain characteristics are shown
with a compensation capacitor (CC) of 0.0033µF, giving the
error amplifier a pole at 240Hz, with phase rolling off to 90°
and staying there. The overall loop has a gain of 77dB at low
frequency rolling off to unity gain at 20kHz. Phase shows a
2-pole characteristic until the ESR of the output capacitor
brings it back above 10kHz. Phase margin is about 60° at
unity-gain.
V
OUT
= 10V
IN
V
OUT
= 5V, I
= 500mA
OUT
C
= 100µF, 10V, AVX TPS
60
C
= 3.3nF, R = 0
C
C
L = 10µH
GAIN
40
PHASE
20
0
0
Analog experts will note that around 1kHz, phase dips to
within 20° of the zero phase margin line. This is typical of
switching regulators because of the 2-pole rolloff generated
by the output capacitor and the compensation network. This
region of low phase is not a problem as long as it does not
occur near unity-gain. In practice, the variability of output
capacitorESRtendstodominateallothereffectswithrespect
to loop response. Variations in ESR will cause unity-gain to
–20
–50
0.01
0.1
1
10
100
100
FREQUENCY (kHz)
LT1511 • F10
Figure 10. Overall Loop Phase and Gain
Undervoltage Lockout
See Application Information in LT1376 data sheet.
U
PACKAGE DESCRIPTION Dimensions in inches (millimeters) unless otherwise noted.
N8 Package
8-Lead PDIP (Narrow 0.300)
(LTC DWG # 05-08-1510)
0.400*
(10.160)
MAX
0.130 ± 0.005
(3.302 ± 0.127)
0.300 – 0.325
(7.620 – 8.255)
0.045 – 0.065
(1.143 – 1.651)
8
1
7
6
5
0.065
(1.651)
TYP
0.009 – 0.015
(0.229 – 0.381)
0.255 ± 0.015*
(6.477 ± 0.381)
0.125
(3.175)
MIN
0.005
0.015
(0.380)
MIN
(0.127)
MIN
+0.025
–0.015
0.325
2
4
+0.635
8.255
3
(
)
–0.381
0.100 ± 0.010
(2.540 ± 0.254)
0.018 ± 0.003
(0.457 ± 0.076)
N8 0695
*THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.
MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.010 INCH (0.254mm)
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tationthattheinterconnectionofitscircuitsasdescribedhereinwillnotinfringeonexistingpatentrights.
19
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