DC799A - Demo Manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 799
SYNCHRONOUS BUCK-BOOST CONVERTER WITH AUTOMATIC BURST MODE
LTC3442EDE
DESCRIPTION
Demonstration Circuit 799 is a high efficiency synchronous 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 BuckBoost 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 Automatic Burst Mode operation and programmable average 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 (TA = 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 VOUT
VIN = 2.5V to 5.5V, IOUT = 0A to 1.1A
3.3V ±4%
Maximum Output Current
VIN = 2.5V
1.1A
Maximum Output Current
VIN = 2.7V
1.2A
Typical Output Ripple VOUT
VIN = 3.6V, IOUT = 1.1A (20MHz BW)
45mVPP
Typical Switching Frequency
RT=43.2K
1MHz
VIN = 4.2V, IOUT = 0.2A
93% Typical
VIN = 4.2V, IOUT = 1.0A
90% Typical
Off (40°C to 85°C)
0.4V MAX
On (-40°C to 85°C)
1.4V MIN
Efficiency (Fixed Frequency Mode)
On/Off Control
QUICK START PROCEDURE
Demonstration circuit 799 is easy to set up to evaluate the performance of the LTC3442. Refer to Figure 1
for proper measurement equipment setup and follow
the procedure below:
1
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 799
SYNCHRONOUS BUCK-BOOST CONVERTER WITH AUTOMATIC BURST MODE
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.
2.
3.
NOTE: Make
RUN
JP2
DISABLE
JP3
AUTO ON
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.
With power off, connect the input power supply to
Vin and GND.
sure that the input voltage does not ex-
ceed 5.5V.
Place jumpers in the following positions:
JP1
Turn on the power at the input.
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.
GRAPHICS
Figure 1. Proper Measurement Equipment Setup
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 799
SYNCHRONOUS BUCK-BOOST CONVERTER WITH AUTOMATIC BURST MODE
GND
VIN
Figure 2. Measuring Input or Output Ripple
Efficiency vs. Load
100%
90%
80%
Efficiency%
70%
60%
50%
40%
2.7Vin PWM
30%
3.6Vin PWM
20%
2.7Vin Burst
10%
4.2Vin Burst
4.2Vin PWM
3.6Vin Burst
0%
0.1
1
10
100
1000
10000
Iout (mA)
Figure 3. Efficiency of DC799
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 799
SYNCHRONOUS BUCK-BOOST CONVERTER WITH AUTOMATIC BURST MODE
Figure 4. Load Transient Response (Vin=3.6V; top trace: Vout, 100mV/div; bottom trace: Iout load step: 200mA to 1.2A)
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 799
SYNCHRONOUS BUCK-BOOST CONVERTER WITH AUTOMATIC BURST MODE
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