QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 755
600KHZ, 1A SYNCHRONOUS BUCK-BOOST CONVERTER
1
LTC3443
DESCRIPTION
Demonstration Circuit 755 is a constant-frequency
synchronous Buck-Boost converter using the
LTC3443. The input range is from 2.4V to 5.5V,
making it ideal for single-cell lithium-ion or three-
cell NiCd/NiMH battery applications. This
converter provides up to 95% efficiency, much
higher than traditional Buck-Boost converters. For
2.5V minimum input voltage, this converter can
provide up to 1A load current.
The output voltage is set at 3.3V. A different output
voltage in the range of 2.4V to 5.25V can be
obtained by changing one of the feedback
resistors. The switching frequency is set at
600kHz, which is a good trade-off between
efficiency and size. Applying twice the desired
frequency at the MODE/SYNC pin can also
synchronize the switching frequency between
690kHz to 1.2MHz. In shutdown, the IC draws
less than 1
µ
A.
When using long wire connection to the input
sources (such as wall adaptors), there can be
input over voltage transients during initial plug-in.
C8 is installed on DC755 to damp the possible
voltage transients. C8 is not needed for any
application when input source is close to the
regulator. Please refer to Application Note 88 for
details.
Design files for this circuit board are available.
Call the LTC factory.
Table 1. Performance Summary (T
A
= 25°C unless otherwise noted)
PARAMETER CONDITION VALUE
Minimum Input Voltage -40
°
C to 85
°
C 2.4V (2.5V minimum input for
1A load)
Maximum Input Voltage -40
°
C to 85
°
C 5.5V
Output Voltage V
OUT
V
IN
= 2.5V to 5.5V, I
OUT
= 0A to 1A 3.3V ±4%
Maximum Output Current V
IN
= 2.5V 1A
Typical Output Ripple V
OUT
V
IN
= 3.0V, I
OUT
= 1A (20MHz BW) 12mV
PP
(measured at C5)
30mV
PP
(measured across TP1
and TP2)
Typical Switching Frequency 600kHz
Efficiency (Fixed Frequency Mode) V
IN
= 4.2V, I
OUT
= 0.2A
V
IN
= 4.2V, I
OUT
= 1A
95% Typical
91% Typical
Off (40
°
C to 85
°
C) 0.4V MAX
On/Off Control On (-40
°
C to 85
°
C) 1.4V MIN
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 755
600KHZ, 1A SYNCHRONOUS BUCK-BOOST CONVERTER
2
QUICK START PROCEDURE
Demonstration circuit 755 is easy to set up to
evaluate the performance of the LTC3443. Refer
to Figure 1 for proper measurement equipment
setup and follow the procedure below:
NOTE:
When measuring the input or output voltage
ripple, care must be taken to avoid a long ground
lead on the oscilloscope probe. Measure the input
or output voltage ripple by touching the probe tip
directly across the Vin or Vout and GND terminals.
See Figure 2 for proper scope probe technique.
1.
Place jumpers in the following positions:
JP1
RUN
FIXED FREQ.
2.
With power off, connect the input power supply
to Vin and GND.
3.
Turn on the power at the input.
NOTE:
Make sure that the input voltage does not
exceed 5.5V.
4.
Check for the proper output voltage. Vout =
3.17V to 3.43V.
NOTE:
If there is no output, temporarily
disconnect the load to make sure that the load
is not set too high.
5.
Once the proper output voltage is established,
adjust the load within the operating range and
observe the output voltage regulation, ripple
voltage, efficiency and other parameters.
JP2
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 755
600KHZ, 1A SYNCHRONOUS BUCK-BOOST CONVERTER
3
GRAPHICS
Figure 1. Proper Measurement Equipment Setup
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 755
600KHZ, 1A SYNCHRONOUS BUCK-BOOST CONVERTER
4
Figure 2. Measuring Input or Output Ripple
Efficiency vs. Load
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
0.1 1 10 100 1000
Iout (mA)
Efficiency%
2.7Vin P WM
3.6Vin P WM
4.2Vin P WM
2.7Vin B urst
3.6Vin B urst
4.2Vin B urst
F i g u r e 3 . Efficiency of DC755
VIN
GND
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 755
600KHZ, 1A SYNCHRONOUS BUCK-BOOST CONVERTER
5
Figure 4. Load Transient Response (Vin=3.3V; Channel 1: Vout, 100mV/div; Channel4: Iout load step: 100mA to 1A)
5
5
4
4
3
3
2
2
1
1
D D
C C
B B
A A
4
9
5
8
10
12
11
263
7
1
SW1
PVIN
SW2
VOUT
VIN
FB
VC
GNDPGNDPGND
MODE/SYNC
SHDN/SS
Linear Technology Corporation
LTC3443EDE
Bill Of Material
Demo Bd. #755A
6/20/2005
Item Qty Reference Part Description Manufacture / Part #
1 1 C1 Cap., X5R 10uF 6.3V 20% Taiyo Yuden JMK212BJ106MG-T
2 1 C2 Cap., X5R 0.047uF 16V 20% AVX 0402YD473MAT2A
3 1 C3 Cap., X7R 560pF 16V 20% AVX 0402YC561MAT2A
4 0 C4 (Opt) Cap., NPO 10pF 25V 10% AVX 04023A100KAT2A
5 1 C5 Cap., X5R 47uF 6.3V 20% Taiyo Yuden JMK325BJ476MM-T
6 1 C6 Cap., X5R 1uF 6.3V 10% Taiyo Yuden JMK107BJ105KA-T
7 1 C7 Cap., NPO 150pF 25V 5% AVX 04023A151JAT2A
8 1 C8 Cap., Tant. 47uF 10V 20% AVX TAJB476M010
9 0 C9 (Opt) Cap., X7R 1000pF 25V 20% AVX 04023C102MAT2A
10 2 D2,D1 Schottky Diodes, 1A/20V Philips PMEG2010EA
11 1 D3 Schottky Diodes, 1A/20V ON SEMI. MBRM120ET3
12 2 JP1,JP2 Headers, 3 Pins 2mm Ctrs. CommConn Con Inc. 2802S-03G2
13 2 XJP1-XJP2 SHUNT, .079" CENTER COMM-CON CCIJ2MM-138GW
14 1 L1 Inductor, 6.0uH Sumida CDRH6D28-6R0NC
15 1 R1 Res., Chip 1.0M 1/16W 5% AAC CR05-105JM
16 1 R2 Res., Chip 15K 1/16W 5% AAC CR05-153JM
17 1 R3 Res., Chip 200K 0.06W 1% AAC CR05-2003FM
18 1 R4 Res., Chip 340K 1/16W 1% AAC CR05-3403FM
19 1 R6 Res., Chip 2.2K 0.06W 5% AAC CR05-222JM
20 0 R7 (Opt) Res., Chip 2.0 0.06W 1% AAC CR05-2R00FM
22 1 U1 I.C., Buck Converter Linear Tech. Corp. LTC3443EDE
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