DC1159A - Demo Manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1159A
4MHZ, 1.25A MONOLITHIC SYNCHRONOUS BUCK REGULATOR
LTC3565
DESCRIPTION
Demonstration circuit 1159A is a high efficiency
monolithic synchronous buck regulator using a
constant frequency, current mode LTC3565. Its
high switching frequency of 2.25MHz allows the
use of small surface mount inductors and capacitors. Supply current during operation is typically
only 20uA, and drops to below 1uA in shutdown.
The 2.5V to 5.5V input voltage range makes the
Table 1.
LTC3565 ideally suited for single Li-Ion batterypowered or 3.3V to 5V input voltage applications.
100% duty cycle provides low dropout operation,
extending battery life in portable systems. Automatic Burst Mode® operation increases efficiency
at light loads, further extending battery runtime.
Gerber files for this circuit are available. Call
the LTC Factory.
Performance Summary (TA = 25ºC)
PARAMETER
CONDITION
VALUE
Input Voltage
Output Voltage
2.5V to 5.5V
IOUT=0A to 1.25A
VOUT ± 1%
Maximum Output Current
1.25A
DC Supply Current
VIN = 3.3V, VOUT = 1.8V, IOUT = 0A
<100µA
Nominal Switching Frequency
VIN = 3.3V, VOUT = 1.8V, IOUT = 1.25A
2.25MHz
QUICK START PROCEDURE
The DC1159A is easy to set up to evaluate the
performance of the LTC3565. Refer to Figure 2
for the proper measurement equipment setup.
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 the measurement example diagram in Figure 1 for proper scope probe measuring technique.
Please follow the procedure outlined below for
proper operation.
1. Connect the input power supply to the VIN
and GND terminals. Connect the load between
the VOUT and GND terminals.
2. Before proceeding to operation, insert
jumper shunt XJP1 into the pulse-skip mode,
jumper shunt XJP2 into the OFF position and
insert one jumper shunt into XJP3, XJP4, or
XJP5 for an output voltage of 1.8V, 1.5V, or
1.2V respectively. Set the load output current to
less than 1.25A. An optional output voltage can
be set by populating resistor RFB5 and moving
the shunt to header JP5.
3. Apply 5V at VIN. Measure VOUT; it should
read 0V. If desired, one can measure the shutdown supply current at this point. The supply current will be less than 10 µA in shutdown.
4. Turn on VOUT by changing shunt XJP2 from
the OFF position to the ON position. The output voltage should measure according to the
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1159A
4MHZ, 1.25A MONOLITHIC SYNCHRONOUS BUCK REGULATOR
voltage set by the shunt in headers JP2, JP3, or
JP4.
5. Vary the input voltage between 2.5V and
5.5V and the output voltage should be within +/1% tolerance.
Warning - If the power for the demo board is
supplied with long leads, the input voltage at the
part could “ring”, which could affect the operation
of the circuit or even exceed the maximum voltage rating of the IC. To eliminate the ringing,
insert a small tantalum capacitor on the pads
6. Vary the VOUT load current from 0 to 1.25A,
and the output voltage should be within a tolerance of +/- 1%.
7. Observe the switch node, pin 4. The waveform should be a rectangular, pulse-width
modulated one, with a frequency of approx.
2.25 MHz.
between the input power and return terminals on
the bottom of the demo board. The ESR of the
tantalum will dampen the (possible) ringing voltage due to the use of long input leads. On a
normal, typical PCB, with short traces, the capacitor is not needed.
Figure 1. Measuring Input or Output Ripple
Figure 2. Proper Measurement Equipment Setup
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1159A
4MHZ, 1.25A MONOLITHIC SYNCHRONOUS BUCK REGULATOR
Load Step Response
Figure 3. Load Step Response
Vin = 3.3V, Vout = 1.8V, 1A Load Step (250mA <-> 1.25A), Fsw = 2.25 MHz
Trace 3: Output Voltage (100mV/div – AC coupled)
Trace 4: Output Current (500mA/div)
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1159A
4MHZ, 1.25A MONOLITHIC SYNCHRONOUS BUCK REGULATOR
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