QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 799
SYNCHRONOUS BUCK-BOOST CONVERTER WITH AUTOMATIC BURST MODE
1
LTC3442EDE
DESCRIPTION
Demonstration Circuit 799 is a high efficiency syn-
chronous Buck-Boost converter using the LTC3442.
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 2.7V minimum input voltage,
this converter can provide up to 1.2A 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 1MHz, which is a good
trade-off between efficiency and size. Adjusting RT
can program the frequency between 300kHz to 2MHz.
In shutdown, the IC itself draws less than 1µA.
The LTC3442 has manual or programmable Auto-
matic Burst Mode operation and programmable aver-
age input current limit.
When using long wire connections to the input
source (such as wall adaptors), there can be input
over voltage transients during initial plug-in. C2 is
installed on DC799 to damp the possible voltage
transients. C2 is not needed for any application when
the 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.
LTC is a trademark of Linear Technology Corporation
Table 1.
Performance Summary (T
A
= 25°C unless otherwise noted)
PARAMETER CONDITION VALUE
Minimum Input Voltage -40
°
C to 85
°
C 2.4V
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 1.1A 3.3V ±4%
Maximum Output Current V
IN
= 2.5V 1.1A
Maximum Output Current V
IN
= 2.7V 1.2A
Typical Output Ripple V
OUT
V
IN
= 3.6V, I
OUT
= 1.1A (20MHz BW) 45mV
PP
Typical Switching Frequency RT=43.2K 1MHz
Efficiency (Fixed Frequency Mode) V
IN
= 4.2V, I
OUT
= 0.2A
V
IN
= 4.2V, I
OUT
= 1.0A
93% Typical
90% Typical
Off (40
°
C to 85
°
C) 0.4V MAX
On/Off Control
On (-40
°
C to 85
°
C) 1.4V MIN
QUICK START PROCEDURE
Demonstration circuit 799 is easy to set up to evalu-
ate the performance of the LTC3442. Refer to Figure 1
for proper measurement equipment setup and follow
the procedure below:
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 799
SYNCHRONOUS BUCK-BOOST CONVERTER WITH AUTOMATIC BURST MODE
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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 out-
put 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
DISABLE
JP3 AUTO ON
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 ex-
ceed 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, ad-
just the load within the operating range and ob-
serve the output voltage regulation, ripple voltage,
efficiency and other parameters.
GRAPHICS
Figure 1.
Proper Measurement Equipment Setup
JP2
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 799
SYNCHRONOUS BUCK-BOOST CONVERTER WITH AUTOMATIC BURST MODE
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Figure 2.
Measuring Input or Output Ripple
Figure 3.
Efficiency of DC799
VIN
GND
Efficiency vs. Load
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
0.1 1 10 100 1000 10000
Iout (mA)
Efficiency%
2.7Vin PWM
3.6Vin PWM
4.2Vin PWM
2.7Vin Burst
3.6Vin Burst
4.2Vin Burst
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 799
SYNCHRONOUS BUCK-BOOST CONVERTER WITH AUTOMATIC BURST MODE
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Figure 4. Load Transient Response (Vin=3.6V; top trace: Vout, 100mV/div; bottom trace: Iout load step: 200mA to 1.2A)
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 799
SYNCHRONOUS BUCK-BOOST CONVERTER WITH AUTOMATIC BURST MODE
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