LT1930ES5 Linear Technology, LT1930ES5 Datasheet - Page 6

• Manufacturer Part Number: LT1930ES5
• Manufacturer: Linear Technology

Specifications of LT1930ES5

• Dc To Dc Converter Type: Step Up
• Number Of Outputs: 1
• Pin Count: 5
• Input Voltage: 16V
• Output Voltage: 1.255 to 34V
• Switching Freq: 1400KHz
• Output Current: 2A
• Package Type: TSOT-23
• Output Type: Adjustable
• Switching Regulator: Yes
• Line Regulation: 0.05%/V
• Mounting: Surface Mount
• Input Voltage (min): 2.45V
• Operating Temperature Classification: Industrial
• Lead Free Status / Rohs Status: Not Compliant

APPLICATIONS
LT1930/LT1930A
CAPACITOR SELECTION
Low ESR (equivalent series resistance) capacitors should
be used at the output to minimize the output ripple voltage.
Multi-layer ceramic capacitors are an excellent choice, as
they have extremely low ESR and are available in very
small packages. X5R dielectrics are preferred, followed by
X7R, as these materials retain the capacitance over wide
voltage and temperature ranges. A 4.7 F to 10 F output
capacitor is sufficient for most applications, but systems
with very low output currents may need only a 1 F or 2.2 F
output capacitor. Solid tantalum or OSCON capacitors can
be used, but they will occupy more board area than a
ceramic and will have a higher ESR. Always use a capacitor
with a sufficient voltage rating.
Ceramic capacitors also make a good choice for the input
decoupling capacitor, which should be placed as close as
possible to the LT1930/LT1930A. A 1 F to 4.7 F input
capacitor is sufficient for most applications. Table 3 shows
a list of several ceramic capacitor manufacturers. Consult
the manufacturers for detailed information on their entire
selection of ceramic parts.
Table 3. Ceramic Capacitor Manufacturers
Taiyo Yuden
AVX
Murata
The decision to use either low ESR (ceramic) capacitors or
the higher ESR (tantalum or OSCON) capacitors can affect
the stability of the overall system. The ESR of any capaci-
tor, along with the capacitance itself, contributes a zero to
the system. For the tantalum and OSCON capacitors, this
zero is located at a lower frequency due to the higher value
of the ESR, while the zero of a ceramic capacitor is at a
much higher frequency and can generally be ignored.
A phase lead zero can be intentionally introduced by
placing a capacitor (C3) in parallel with the resistor (R1)
between V
of the zero is determined by the following equation.
6
Z
2
OUT
•
R C
and V
1
1
•
[phone]
[phone]
[phone]
3
U
FB
as shown in Figure 1. The frequency
INFORMATION
U
W
www.t-yuden.com
www.avxcorp.com
www.murata.com
U
By choosing the appropriate values for the resistor and
capacitor, the zero frequency can be designed to improve
the phase margin of the overall converter. The typical
target value for the zero frequency is between 35kHz to
55kHz. Figure 3 shows the transient response of the step-
up converter from Figure 1 without the phase lead capaci-
tor C3. The phase margin is reduced as evidenced by more
ringing in both the output voltage and inductor current. A
10pF capacitor for C3 results in better phase margin,
which is revealed in Figure 4 as a more damped response
and less overshoot. Figure 5 shows the transient response
when a 33 F tantalum capacitor with no phase lead
capacitor is used on the output. The higher output voltage
ripple is revealed in the upper waveform as a set of double
lines. The transient response is not greatly improved
which implies that the ESR zero frequency is too high to
increase the phase margin.
CURRENT
CURRENT
Figure 3. Transient Response of Figure 1's Step-Up
Converter without Phase Lead Capacitor
Figure 4. Transient Response of Figure 1's Step-Up
Converter with 10pF Phase Lead Capacitor
LOAD
AC COUPLED
AC COUPLED
LOAD
AC COUPLED
AC COUPLED
0.2V/DIV
0.5A/DIV
0.2V/DIV
0.5A/DIV
250mA
150mA
250mA
150mA
V
V
OUT
I
OUT
LI
I
LI
50 s/DIV
50 s/DIV
1930 F04
1930 F03