LT1576IS8-5#PBF Linear Technology, LT1576IS8-5#PBF Datasheet - Page 22

• Manufacturer Part Number: LT1576IS8-5#PBF
• Description: IC REG SW 5V 1.5A STEPDOWN 8SOIC
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LT1576IS8-5#PBF

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 5V
• Current - Output: 1.5A
• Frequency - Switching: 200kHz
• Voltage - Input: 5 ~ 25 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -

LT1576/LT1576-5
APPLICATIONS
How Do I Test Loop Stability?
The “standard” compensation for LT1576 is a 100pF
capacitor for C
will work for most applications, the “optimum” value for
loop compensation components depends, to various ex-
tent, on parameters which are not well controlled. These
include inductor value ( 30% due to production toler-
ance, load current and ripple current variations), output
capacitance ( 20% to 50% due to production tolerance,
temperature, aging and changes at the load), output
capacitor ESR ( 200% due to production tolerance, tem-
perature and aging), and finally, DC input voltage and
output load current . This makes it important for the
designer to check out the final design to ensure that it is
“robust” and tolerant of all these variations.
22
C
, with R
INPUT SUPPLY
ADJUSTABLE
U
C
INFORMATION
= 0 . While this compensation
U
10mV/DIV
REGULATOR
SWITCHING
W
5A/DIV
ADJUSTABLE
DC LOAD
Figure 13. Loop Stability Test Circuit
Figure 14. Loop Stability Check
U
+
0.2ms/DIV
50
100Hz TO 1kHz
100mV TO 1V
100 F TO
1000 F
TO
OSCILLOSCOPE
SYNC
I check switching regulator loop stability by pulse loading
the regulator output while observing transient response at
the output, using the circuit shown in Figure 13. The
regulator loop is “hit” with a small transient AC load
current at a relatively low frequency, 50Hz to 1kHz. This
causes the output to jump a few millivolts, then settle back
to the original value, as shown in Figure 14. A well behaved
loop will settle back cleanly, whereas a loop with poor
phase or gain margin will “ring” as it settles. The number
of rings indicates the degree of stability, and the frequency
of the ringing shows the approximate unity-gain fre-
quency of the loop. Amplitude of the signal is not particu-
larly important, as long as the amplitude is not so high that
the loop behaves nonlinearly.
P-P
3300pF
470
1576 F14
RIPPLE FILTER
4.7k
V
I
BEFORE FILTER
V
I
AFTER FILTER
LOAD PULSE
THROUGH 50
f 780Hz
V
I
AFTER FILTER
OUT
OUT
OUT
OUT
OUT
OUT
= 50mA
= 500mA
= 500mA
AT
AT
AT
330pF
1576 F13
TO X1
OSCILLOSCOPE
PROBE