DC1610A - Demo Board

DEMO CIRCUIT 1610A
QUICK START GUIDE
LTC3604
LTC3604EUD
2.5A, 15V, MONOLITHIC SYNCHRONOUS
STEP-DOWN REGULATOR
DESCRIPTION
Demonstration circuit 1610 is a step-down converter,
using the LTC3604 monolithic synchronous buck
regulator. The DC1610A has a maximum input voltage
15V, and is capable of delivering up to 2.5A of output
current at a minimum input voltage of 3.6V. The output voltage of the DC1610A can be set as low as 0.6V,
the reference voltage of the LTC3604. At low load currents, the DC1610A operates in discontinuous mode,
and during shutdown, it consumes less than 40 uA of
quiescent current. In continuous mode operation, the
DC1610A is a high efficiency circuit - over 80%. The
DC1610A can track another voltage with the LTC3604
track function. Because of the high switching frequency of the LTC3604, which is programmable up to
4 MHz, the DC1610A uses low profile surface mount
components. All these features make the DC1610A an
ideal circuit for use in Lithium-Ion Battery applications
and distributed power systems. Gerber files for this
circuit are available. Call the LTC Factory.
Design files for this circuit board are available. Call the
LTC factory.
As Shipped Performance Summary
PARAMETER
CONDITIONS
VALUE
Minimum Input Voltage
3.6V
Maximum Input Voltage
15V
GND = Shutdown
Run/Shutdown
VIN = 3.6V to 15V, IOUT = 0A to 2.5A
VIN = Run
1.2V ±4% (1.152V – 1.248V)
VIN = 3.6V to 15V, IOUT = 0A to 2.5A
1.8V ±4% (1.728V – 1.872V)
VIN = 4.5V to 15V, IOUT = 0A to 2.5A
3.3V ±4% (3.168V – 3.432V)
Typical Output Ripple Voltage
VIN = 12V, VOUT = 1.8V, IOUT = 2.5A (20 MHz BW)
< 20mVP–P
Burst Mode
VIN = 12V, VOUT = 1.8V
< 700 mA
Nominal Switching Frequency
RT = 324k
1 MHz ± 20%
Output Voltage
Regulation
Table 1. Jumper Description
JUMPER
JP1
JP5
JP6
JP7
JP8
JP9
FUNCTION
Vout Setting.
Tracking or Soft-Start (SS)
Mode: Forced Continuous Mode (FCM), Burst Mode, or External Synchronization (SYNC)
Run
Frequency
ITH: Compensation
RANGE/SETTING (DEFAULT)
1.2V
(SS) - TRACK
(FCM) – SYNC – Burst Mode
(ON) - OFF
(1 MHz) - 2 MHz
INT – (EXT)
1
LTC3604
QUICK START PROCEDURE
Demonstration Circuit 1610 is easy to set up to evaluate the performance of the LTC3604. For proper
measurement equipment configuration, set up the circuit according to the diagram in Figure 1. Before proceeding to test, insert shunts into the 1.2V position of the
output voltage header JP1, into the SS (soft-start) position of Track/SS header JP5, into the FCM (Forced Continuous Mode) position of MODE header JP6, into the OFF
position of RUN header JP7, into the 1 MHz position of
FREQ header JP8, and into the EXT position of ITH header
JP9.
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 measurement technique.
output current to any current less than 400 mA. Observe the discontinuous mode of operation at the
switch node, and measure the output ripple voltage. It
should measure less than 150 mV.
Insert the JP7 shunt into the OFF position and move
the shunt in the 1.2V output JP1 header into any of the
two remaining output voltage option headers: 1.8V
(JP2) or 3.3V (JP3). Just as in the 1.2V Vout test, the
output voltage should read Vout +/- 2% tolerance under static line and load conditions and +/- 1% tolerance under dynamic line and load conditions (+/- 2%
total). Also, the circuit operation in discontinuous
mode will be the same.
When finished, turn off the circuit by inserting the
shunt in header JP7 into the OFF position.
Low Output Voltage, 2MHz Operation
With the DC1610 set up according to the proper
measurement configuration and equipment in Figure
1, apply 6.3V at Vin (Do not hot-plug Vin or increase
Vin over the rated maximum supply voltage of 15V, or
the part may be damaged.). Measure Vout; it should
read 0V. Turn on the circuit by inserting the shunt in
header JP7 into the ON position. The output voltage
should be regulating. Measure Vout - it should measure 1.2V +/- 2% (1.176V to 1.224V).
Vary the input voltage from 3.6V to 15V and adjust the
load current from 0 to 2.5A. Set the input voltage to
15V and the output current to 2.5A. Measure the output ripple voltage; it should measure less than 20
mVAC.
Observe the voltage waveform at the switch pins (the
other side of the inductor from the output). Verify the
switching frequency is between 800 kHz and 1.2 MHz
(T = 1.25 us and 0.833 us), and that the switch node
waveform is rectangular in shape.
Change the JP6 shunt from forced continuous mode to
Burst Mode. Also set the input voltage to 12V and the
2
In applications with low output voltages of less than
1.2V, and frequencies of 2 MHz or higher, the inductor
ripple current will be reduced significantly such that the
internal current comparator will not be able to clearly
differentiate it from surrounding noise. Sporadic ckt.
operation will result. To avoid this effect, replace the
standard 1 uH inductor with a 0.47 uH inductor. This
will make the inductor ripple current large enough so
that the circuit operation will not be affected.
Warning - If the power for the demo board is carried in
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 (which, of
course, may damage the IC). To eliminate the ringing, a
small tantalum capacitor has been inserted on the pads
between the input power and return terminals on the
bottom of the demo board. The (greater) ESR of the
tantalum capacitor 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.
LTC3604
Figure 1.
Proper Equipment Measurement Set-Up
Figure 2. Measuring Input or Output Ripple
3
LTC3604
Normal Switching Frequency & Output Ripple Voltage
Waveforms
Figure 3. Switch Node & Output Ripple Voltage Waveforms
VIN = 12V, VOUT = 1.8V, IOUT = 2.5A, FSW = 2 MHz
Trace 3: Output Ripple Voltage (20 mV/div AC)
Trace 2: Switch Voltage (10 V/div)
4
LTC3604
Load Step Response Waveform
Figure 4. Load Step Response
VIN = 12V, VOUT = 1.8V, 2.5A Load Step (0A <-> 2.5A)
Forced Continuous Mode FSW = 2 MHz
Trace 3: Output Voltage (50mV/div AC)
Trace 4: Output Current (1A/div)
5
LTC3604
6
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