DC1574A - Demo Manual

DEMO CIRCUIT 1574A
LTC3612
QUICK START
GUIDE
LTC3612
3A, 4MHz, MONOLITHIC SYNCHRONOUS
STEP-DOWN REGULATOR
DESCRIPTION
Demo Circuit 1574 is a high efficiency, high frequency step-down converter, incorporating the
LTC3612 monolithic synchronous regulator. The
DC1574A has an input voltage range of 2.25V to
5.5V, and is capable of delivering up to 3A of output
current. The output voltage of the DC1574A can be
set as low as 0.6V, the reference voltage of the
LTC3612. The operating frequency range of the
DC1574A is either set to a fixed 2.25 MHz by connecting the frequency pin to SVin, set by an external resistor, or synchronized to an external clock,
with a range up to 4 MHz. At low load currents, the
DC1574A can operate in either noise sensitive applications, due to the capability of the LTC3612 to
operate in pulse-skipping mode, or in high efficiency applications, because the LTC3612 also has
Burst-Mode capability. The Burst Mode clamp can
be set externally. Of course, in (forced) continuous
mode, or large load current applications, the
DC1574A is a very efficient circuit - over 90%. The
DC1574A consumes less than 200 uA of quiescent
current during sleep operation, and during shutdown, it consumes less than 1 uA. The DC1574A
can track another voltage, due to the LTC3612
track function, for easy power supply sequencing.
Extra features include frequency and current foldback, and an adjustable 0.3V-to-0.6V external reference. Because of the high switching frequency
of the LTC3612, which is programmable up to 4
MHz, the DC1574A uses low profile surface mount
components. All these features make the DC1574A
perfectly suited for portable computer and distributed power applications.
Design files for this circuit board are available. Call the
LTC factory.
As Shipped Performance Summary
PARAMETER
CONDITIONS
VALUE
Minimum Input Voltage
2.25V
Maximum Input Voltage
5.5V
GND = Shutdown
Run/Shutdown
VIN = 2.25V to 5.5V, IOUT = 0A to 3A
VIN = Run
1.2V ±4% (1.152V – 1.248V)
VIN = 2.25V to 5.5V, IOUT = 0A to 3A
1.8V ±4% (1.728V – 1.872V)
VIN = 3.1V to 5.5V, IOUT = 0A to 3A
2.5V ±4% (2.4V – 2.6V)
VIN = 3.9V to 5.5V, IOUT = 0A to 3A
3.3V ±4% (3.168V – 3.432V)
Typical Output
Ripple Voltage
VIN = 5V, VOUT = 1.8V, IOUT = 3A
(20 MHz BW)
<30mVP–P
Burst Mode
VIN = 5V, VOUT = 1.8V
<600 mA
Pulse-Skip Mode
VIN = 5V, VOUT = 1.8V
<500 mA
Nominal Switching
Frequency
RT = 165k
2 MHz ± 20%
Output Voltage
Regulation
1
LTC3612
Table 1. Jumper Description
JUMPER FUNCTION
JP1
Output Voltage Setting.
J1
Mode: Forced Continuous Mode (FCM), Burst Mode (BM or BMEC), or Pulse-Skip Mode(SYNC)
J2
Run
J3
Tracking (TRACK), Internal Soft-Start (INT SS), or External Soft-Start (EXT SS)
J4
DDR Memory Termination
J5
External or Internal ITH Compensation
J6
Frequency Setting: Timing Resistor (RT), Internally Synchronized (INT SYNC - 2.25 MHz), or
Externally Synchronized (EXT SYNC)
J9
External Burst Mode Clamp Voltage
RANGE/SETTING (DEFAULT)
1.2V
(FCM) – BMEC – BM - PSM
(ON) - OFF
(EXT SS) – INT SS - TRACK
(OFF) - ON
(EXT) – INT
(Rt) – INT SYNC – EXT SYNC
(SET) – EXT
QUICK START PROCEDURE
Demonstration Circuit 1574 is easy to set up to evaluate the performance of the LTC3612. 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 FCM (Forced Continuous Mode) position of MODE header J1, into the OFF
position of RUN header J2, into the EXT SS (external softstart) position of Track/SS header J3, into the OFF position of DDR header J4, into the EXT (external) position of
COMP header J5, into the Rt position of Rt/SYNC header
J6, and into the SET position of VBMCV header J9.
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.
With the DC1574 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 5.5V, or
the part may be damaged.). Measure Vout; it should
read 0V. Turn on the circuit by inserting the shunt in
header J2 into the ON position. The output voltage
should be regulating. Measure Vout - it should measure 1.2V +/- 2% (1.176V to 1.224V).
2
Vary the input voltage from 2.25V to 5.5V and adjust
the load current from 0 to 3A. Vout should regulate
around 1.2V. Measure the output ripple voltage; it
should measure less than 30 mVAC.
Observe the voltage waveform at the switch pins (the
other side of the inductor from the output). Verify the
switching frequency is between 1.6 MHz and 2.4 MHz
(T = 625 ns and 416 ns), and that the switch node
waveform is rectangular in shape.
Change the J1 shunt from forced continuous mode to
Burst Mode or pulse-skip mode. Set the input voltage
to 5V and the output current to any current less than
600 mA. Observe the discontinuous mode of operation at the switch node, and measure the output ripple
voltage. It should measure less than 100 mV.
Insert the J2 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), 2.5V (JP3), or 3.3V (JP4). 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 J2 into
the OFF position.
LTC3612
Figure 1. Proper Measurement Equipment Set-Up
Figure 2. Measuring Input or Output Ripple
3
LTC3612
Normal Switching Frequency & Output Ripple Voltage
Waveforms
Figure 3. Switch Node & Output Ripple Voltage Waveforms
VIN = 3.3V, VOUT = 1.8V, IOUT = 3A, FSW = 2 MHz
Trace 3: Output Ripple Voltage (20 mV/div AC)
Trace 1: Switch Voltage (2 V/div)
4
LTC3612
Load Step Response Waveform
Figure 4. Load Step Response
VIN = 3.3V, VOUT = 1.8V, 2.5A Load Step (0.5A <-> 3A)
Forced Continuous Mode FSW = 2 MHz
Trace 3: Output Voltage (100mV/div AC)
Trace 4: Output Current (2A/div)
5
LTC3612
6
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