LT1302CN8-5 Linear Technology, LT1302CN8-5 Datasheet - Page 9

• Manufacturer Part Number: LT1302CN8-5
• Description: IC DC/DC CONV STEP-UP 5V 8-DIP
• Manufacturer: Linear Technology
• Type: Step-Up (Boost)r

Specifications of LT1302CN8-5

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 5V
• Current - Output: 600mA
• Frequency - Switching: 220kHz
• Voltage - Input: 2 ~ 8 V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Through Hole
• Package / Case: 8-DIP (0.300", 7.62mm)
• Power - Output: 700mW
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

APPLICATIONS
Frequency Compensation
Obtaining proper RC values for the frequency compensa-
tion network is largely an empirical procedure, since
variations in input and output voltage, topology, capacitor
ESR and inductance make a simple formula elusive. As an
example, consider the case of a 2.5V to 5V boost converter
supplying 500mA. To determine optimum compensation,
the circuit is built and a transient load is applied to the
circuit. Figure 7 shows the setup.
In Figure 7a, the V
output voltage is maintained and transient response is
good, switch current rises instantaneously to the internal
current limit upon application of load. This is an undesir-
able situation as it places maximum stress on the switch
and the other power components. Additionally, efficiency
is well down from its optimal value. Next, a 0.1 F capacitor
is connected with no resistor. Figure 7b details response.
Although the circuit eventually stabilizes, the loop is quite
underdamped. Initial output “sag” exceeds 5%. Aberrant
AC COUPLED
I
LOAD
100mV/DIV
510mA
Figure 7a. V
Low Frequency Components Under Load
10mA
V
OUT
2.5V
C1, C2, C3 = AVX TPS SERIES
D1 = MOTOROLA MBRS130LT3
L1 = COILCRAFT DO3316-103K
V
IN
C
U
C
pin is simply left floating. Although
+
Pin Left Unconnected. Output Shows
INFORMATION
C1
330 F
U
+
2ms/DIV
C2
220 F
W
+
Figure 7. Boost Converter with Simulated Load
L1
10 H
D1
C3
220 F
1302 F07a
U
0.1 F
SW
PGND
GND
V
IN
LT1302-5
behavior in the 4th graticule is the result of the LT1302’s
Burst Mode comparator turning off all switching as output
voltage rises above its threshold.
In Figure 7c, the 0.1 F capacitor has been replaced by a
0.01 F unit. Undershoot is less but the response is still
underdamped. Figure 7d shows the results of the 0.1 F
capacitor and a 10k resistor in series. Now some amount
of damping is observed, and behavior is more controlled.
Figure 7e details response with a 0.01 F/10k series net-
work. Undershoot is down to around 100mV, or 2%. A
slight underdamping is still noticeable.
Finally, a 0.01 F/24k series network results in the re-
sponse shown in Figure 7f. This has optimal damping,
undershoot less than 100mV and settles in less than 1ms.
The V
layouts may inject enough noise to modulate peak switch
current at 1/2 the switching frequency. A small capacitor
connected from V
exceed 1/10 of the compensation capacitor value.
SENSE
SHDN
NC
V
I
T
C
AC COUPLED
I
LOAD
R
100mV/DIV
C
C
510mA
10mA
V
pin is sensitive to high frequency noise. Some
OUT
500
Figure 7b. 0.1 F from V
Better, but More Improvement Needed
MTP3055EL
C
10
2W
to ground will eliminate this. Do not
2ms/DIV
LT1302/LT1302-5
50
1302 F07
C
to Ground.
PULSE
GENERATOR
1302 F07b
9