LT1374CFE#TR Linear Technology, LT1374CFE#TR Datasheet - Page 22
LT1374CFE#TR
Manufacturer Part Number
LT1374CFE#TR
Description
IC SW REG 4.5A ADJ STPDN 16TSSOP
Manufacturer
Linear Technology
Type
Step-Down (Buck)r
Datasheet
1.LT1374CFEPBF.pdf
(32 pages)
Specifications of LT1374CFE#TR
Internal Switch(s)
Yes
Synchronous Rectifier
No
Number Of Outputs
1
Voltage - Output
2.42 ~ 21.5 V
Current - Output
4.5A
Frequency - Switching
500kHz
Voltage - Input
5 ~ 25 V
Operating Temperature
0°C ~ 125°C
Mounting Type
Surface Mount
Package / Case
16-TSSOP Exposed Pad, 16-eTSSOP, 16-HTSSOP
Lead Free Status / RoHS Status
Contains lead / RoHS non-compliant
Power - Output
-
Other names
LT1374CFETR
Available stocks
Company
Part Number
Manufacturer
Quantity
Price
LT1374
APPLICATIONS
Error amplifier transconductance phase and gain are
shown in Figure 11. The error amplifier can be modeled
as a transconductance of 2000µMho, with an output
impedance of 200kΩ in parallel with 12pF. In all practical
applications, the compensation network from V
ground has a much lower impedance than the output
impedance of the amplifier at frequencies above 500Hz.
This means that the error amplifier characteristics them-
selves do not contribute excess phase shift to the loop, and
the phase/gain characteristics of the error amplifier sec-
tion are completely controlled by the external compensa-
tion network.
In Figure 12, full loop phase/gain characteristics are
shown with a compensation capacitor of 1.5nF, giving the
error amplifier a pole at 530Hz, with phase rolling off to 90°
22
LT1374
GND
CURRENT MODE
POWER STAGE
C
Figure 10. Response from V
g
F
–20
–40
m
40
20
= 5.3A/V
0
Figure 9. Model for Loop Response
10
V
R
C
C
C
C
100
U
PHASE
GAIN
AMPLIFIER
FREQUENCY (Hz)
ERROR
–
+
INFORMATION
1k
U
2.42V
V
SW
FB
10k
C
W
V
V
I
100k
OUT
Pin to Output
IN
OUT
= 10V
= 2A
= 5V
1374 F10
1M
R1
R2
40
0
–40
–80
–120
+
U
ESR
C1
C
OUTPUT
pin to
1374 F09
and staying there. The overall loop has a gain of 74dB at
low frequency, rolling off to unity-gain at 100kHz. Phase
shows a two-pole characteristic until the ESR of the output
capacitor brings it back above 10kHz. Phase margin is
about 75° at unity-gain.
Analog experts will note that around 4.4kHz, phase dips
very close to the zero phase margin line. This is typical of
switching regulators, especially those that operate over a
wide range of loads. 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 capacitor ESR tends to
dominate all other effects with respect to loop response.
Variations in ESR will cause unity-gain to 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
(≥ ±3:1).
Figure 11. Error Amplifier Gain and Phase
3000
2500
2000
1500
1000
500
–20
Figure 12. Overall Loop Characteristics
80
60
40
20
0
100
10
V
R
V
V
C
C
ERROR AMPLIFIER EQUIVALENT CIRCUIT
FB 2 × 10
IN
OUT
OUT
C
LOAD
= 1.5nF, R
(
= 10V
= 5V, I
= 100µF, 10V, AVX TPS
100
1k
= 50Ω
–3
)
OUT
C
FREQUENCY (Hz)
FREQUENCY (Hz)
PHASE
= 0, L = 10µH
GAIN
10k
= 2A
1k
GAIN
R
200k
OUT
100k
10k
100k
1M
C
12pF
PHASE
OUT
V
C
1374 F11
1374 F12
10M
1M
200
150
100
50
0
–50
200
150
100
50
0
–50
1374fd