LT1308BCS8#TRPBF Linear Technology, LT1308BCS8#TRPBF Datasheet - Page 14

• Manufacturer Part Number: LT1308BCS8#TRPBF
• Description: IC DC/DC CONV SINGLE CELL 8-SOIC
• Manufacturer: Linear Technology
• Type: Step-Up (Boost)r

Specifications of LT1308BCS8#TRPBF

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 5V
• Current - Output: 1A
• Frequency - Switching: 600kHz
• Voltage - Input: 1 ~ 10 V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -

APPLICATIONS INFORMATION
LT1308A/LT1308B
Ceramic Capacitors
Multilayer ceramic capacitors have become popular, due
to their small size, low cost, and near-zero ESR. Ceramic
capacitors can be used successfully in LT1308A/LT1308B
designs provided loop stability is considered. A tantalum
capacitor has some ESR and this causes an "ESR zero" in
the regulator loop. This zero is benefi cial to loop stability.
Ceramics do not have appreciable ESR, so the zero is lost
when they are used. However, the LT1308A/LT1308B have
external compensation pin (V
be adjusted to achieve stability. A phase lead capacitor can
also be used to tune up load step response to optimum
levels, as detailed in the following paragraphs.
Figure 19 details a 5V to 12V boost converter using either
a tantalum or ceramic capacitor for C2. The input capaci-
tor has little effect on loop stability, as long as minimum
capacitance requirements are met. The phase lead capaci-
tor C
load step response of a 50mA to 500mA load step using a
47μF tantalum capacitor at the output. Without the phase
lead capacitor, there is some ringing, suggesting the
phase margin is low. C
the same load step is pictured in Figure 21. Some phase
margin is restored, improving the response. Next, C2 is
replaced by a 10μF, X5R dielectric, ceramic capacitor.
14
V
5V
IN
+
PL
C1: AVX TAJC476M010
C2: AVX TPSD476M016 (47μF) OR
D1: IR 10BQ015
L1: MURATA LQH6C4R7
parallels feedback resistor R1. Figure 20 shows
TAIYO YUDEN TMK432BJ106MM (10μF)
C1
47μF
Figure 19. 5V to 12V Boost Converter
SHDN
V
V
IN
C
47k
LT1308B
100pF
4.7μH
L1
GND
PL
SW
FB
is then added, and response to
D1
C
10k
R3
) so component values can
R1
100k
R2
11.3k
C
330pF
PL
1308 F19
C2
V
12V
500mA
OUT
CURRENT
CURRENT
CURRENT
Without C
Although the output settles faster than the tantalum case,
there is appreciable ringing, again suggesting phase margin
is low. Figure 23 depicts load step response using the 10μF
ceramic output capacitor and C
no ringing is evident. Ceramic capacitors have the added
benefi t of lowering ripple at the switching frequency due
to their very low ESR. By applying C
series RC at the V
optimize response using ceramic output capacitors.
LOAD
LOAD
LOAD
500mV/DIV
500mV/DIV
500mV/DIV
Figure 20. Load Step Response of LT1308B 5V to 12V
Boost Converter with 47μF Tantalum Output Capacitor
1A/DIV
500mA
1A/DIV
500mA
1A/DIV
500mA
Figure 21. Load Step Response with 47μF Tantalum
Output Capacitor and Phase Lead Capacitor C
50mA
50mA
50mA
V
V
V
OUT
OUT
OUT
I
Figure 22. Load Step Response with 10μF X5R
Ceramic Output Capacitor
I
I
L1
L1
L1
PL
, load step response is pictured in Figure 22.
C
pin, loop response can be tailored to
200μs/DIV
200μs/DIV
200μs/DIV
PL
. Response is clean and
PL
in tandem with the
1308 F20
1308 F21
1308 F22
PL
1308abfb