DEMO CIRCUIT 1461A
LTC3616
QUICK START GUIDE
LTC3616
6A, 4MHz, MONOLITHIC SYNCHRONOUS
DC/DC STEP-DOWN CONVERTER
DESCRIPTION
Demo Circuit 1461 is a high efficiency, high fre-
quency step-down converter, incorporating the
LTC3616 monolithic synchronous regulator. The
DC1461A has an input voltage range of 2.25V to
5.5V, and is capable of delivering up to 6A of output
current. The output voltage of the DC1461A can be
set as low as 0.6V, the reference voltage of the
LTC3616. The operating frequency range of the
DC1461A is either set to a fixed 2.25 MHz by con-
necting the frequency pin to SVin, set by an exter-
nal resistor, or synchronized to an external clock,
with a range up to 4 MHz. At low load currents, the
DC1461A can operate in either noise sensitive ap-
plications, due to the capability of the LTC3616 to
operate in pulse-skipping mode, or in high effi-
ciency applications, because the LTC3616 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
DC1461A is a very efficient circuit - over 90%. The
DC1461A consumes less than 300 uA of quiescent
current during sleep operation, and during shut-
down, it consumes less than 1 uA. The DC1461A
can track another voltage, due to the LTC3616
track function, for easy power supply sequencing.
Extra features include frequency and current fold-
back, and an adjustable 0.3V-to-0.6V external ref-
erence. Because of the high switching frequency
of the LTC3616, which is programmable up to 4
MHz, the DC1461A uses low profile surface mount
components.
All these features make the
DC1461A 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
Minimum Input Voltage
Maximum Input Voltage
Run/Shutdown
CONDITIONS
VALUE
2.25V
5.5V
GND = Shutdown
VIN = Run
1.2V ±4% (1.152V – 1.248V)
1.8V ±4% (1.728V – 1.872V)
2.5V ±4% (2.4V – 2.6V)
3.3V ±4% (3.168V – 3.432V)
<40mVP–P
<1.3A
<1.2A
2 MHz ± 20%
VIN = 2.25V to 5.5V, IOUT = 0A to 6A
Output Voltage
Regulation
VIN = 2.5V to 5.5V, IOUT = 0A to 6A
VIN = 3.3V to 5.5V, IOUT = 0A to 6A
VIN = 4.2V to 5.5V, IOUT = 0A to 6A
Typical Output
Ripple Voltage
Burst Mode
Pulse-Skip Mode
Nominal Switching
Frequency
VIN = 5V, VOUT = 1.8V, IOUT = 6A (20 MHz BW)
VIN = 5V, VOUT = 1.8V
VIN = 5V, VOUT = 1.8V
RT = 165k
1
LTC3616
Table 1.
Jumper Description
JUMPER FUNCTION
JP1
Output Voltage Setting.
J1
Mode: Forced Continuous Mode (FC), 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 (2.25 MHz), or Externally
Synchronized
J7
External Burst Mode Clamp Voltage
RANGE/SETTING (DEFAULT)
1.2V
(FC) – 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 1461 is easy to set up to evalu-
ate the performance of the LTC3616. For proper
measurement equipment configuration, set up the cir-
cuit according to the diagram in
Figure 1.
Before pro-
ceeding to test, insert shunts into the 1.2V position of the
output voltage header JP1, into the FCM (Forced Con-
tinuous Mode) position of MODE header J1, into the OFF
position of RUN header J2, into the EXT SS (external soft-
start) position of Track/SS header J3, into the OFF posi-
tion 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 J7.
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 volt-
age 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 DC1461 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 meas-
ure 1.2V +/- 2% (1.176V to 1.224V).
Vary the input voltage from 2.25V to 5.5V and adjust
the load current from 0 to 6A. Vout should regulate
around 1.2V. Measure the output ripple voltage; it
should measure less than 40 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
1A. Observe the discontinuous mode of operation at
the switch node, and measure the output ripple volt-
age. 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 discon-
tinuous mode will be the same. When finished, turn
off the circuit by inserting the shunt in header J2 into
the OFF position.
2
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