DEMO MANUAL DC1864A
LTC3621-2
17V, 1A Monolithic Synchronous
Step-Down Regulator
DESCRIPTION
Demonstration circuit 1864A is a step-down converter,
capable of delivering up to 1A of output current from a
minimum input voltage of 2.7V. The DC1864A uses the
power-saving
LTC
®
3621-2
2.25MHz monolithic synchro-
nous buck regulator that comes in a tiny 2mm
×
3mm
6-lead DFN package. The LTC3621-2 IC quiescent currents
can be as low as 3.5µA in normal operation, and less
than 0.1µA in shutdown. The output voltage range of the
DC1864A is from as low as 0.6V, the reference voltage of
the LTC3621-2, to as high as the maximum input voltage,
17V. The DC1864A can operate in three distinct operating
modes: Burst Mode
®
for highest efficiency at low output
currents, forced continuous mode for lowest output ripple
voltage, and pulse-skipping mode for the best compromise
operation between the two other modes, by setting the
MODE pin to INTVCC (3.6V), INTVCC/2, or ground re-
spectively. All these features make the DC1864A an ideal
circuit for use in any high efficient, low power application.
Design files for this circuit board are available at
http://www.linear.com/demo
L,
LT, LTC, LTM, Linear Technology, the Linear logo and Burst Mode are registered trademarks
of Linear Technology Corporation. All other trademarks are the property of their respective
owners.
PERFORMANCE SUMMARY
PARAMETER
Input Voltage Range
Output Voltage Range
Run/Shutdown
Output Voltage Regulation
CONDITIONS
Specifications are at T
A
= 25°C
VALUE
2.7V to 17V
0.6V to V
IN
Shutdown
Operating
1.2V ±3% Typ. (1.164V to 1.236V)
1.8V ±3% Typ. (1.746V to 1.854V)
2.5V ±3% Typ. (2.425V to 2.575V)
3.3V ±3% Typ. (3.201V to 3.399V)
5V ±3% Typ. (4.85V to 5.15V)
< 20mV
P-P
2.25MHz ±8%
Burst Mode Operation
Pulse-Skipping
Forced Continuous
I
OUT
< 500mA
3.6V ±8.33% (3.3V to 3.9V)
Typical Output Ripple Voltage
Nominal Switching Frequency
Operation Modes
RUN Pin = GND
RUN Pin = V
IN
V
IN
= 2.7V to 17V, I
OUT
= 0A to 1A
V
IN
= 2.7V to 17V, I
OUT
= 0A to 1A
V
IN
= 2.7V to 17V, I
OUT
= 0A to 1A
V
IN
= 3.5V to 17V, I
OUT
= 0A to 1A
V
IN
= 5.2V to 17V, I
OUT
= 0A to 1A
V
IN
= 12V, V
OUT
= 5V, I
OUT
= 1A (20MHz BW)
MODE Pin = INTVCC
MODE Pin = GND
MODE Pin = INTVCC/2
V
IN
= 12V, V
OUT
= 1.2V
Burst Mode-to-CCM Operation
INTV
CC
Table 1. Jumper Description
JUMPER
JP1
JP2
JP3
FUNCTION/RANGE
Run: ON – OFF.
Mode: Burst Mode Operation (BM) or Pulse-Skipping Mode (PS)
Output Voltage Setting.
SETTING
ON
BM
1.2V
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DEMO MANUAL DC1864A
QUICK START PROCEDURE
Demonstration circuit 1864 is easy to set up to evaluate the
performance of the LTC3621-2. For proper measurement
equipment configuration, set up the circuit according to
the diagram in Figure 1. Before proceeding to test, check
that the shunts are inserted into the correct locations:
1.2V position of the output voltage header JP3, into the
BM (Burst Mode operation) position of MODE header JP2,
and into the ON position of RUN header JP1.
When measuring the input or output voltage ripple, care
must be taken to avoid a long ground lead on the oscil-
loscope 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 DC1864 set up according to the proper measure-
ment configuration and equipment in Figure 1, apply 5V at
VIN (Do not hot-plug VIN or increase VIN over the rated
maximum supply voltage of 17V, or the part may be dam-
aged.). Measure V
OUT
; it should read 1.2V. (If desired, the
quiescent current of the circuit can be monitored now by
swapping the shunt in header JP1 into the OFF position.)
The output voltage should be regulating. Draw 500mA out
of the output and measure V
OUT
— it should measure 1.2V
±2% (1.176V to 1.224V). Verify the switching frequency
is between 1.8MHz and 2.6MHz (t = 55ns and 38ns), and
that the switch node waveform is rectangular in shape.
Vary the input voltage from 2.7V to 17V and the load cur-
rent from 0 to 1A. V
OUT
should regulate around 1.2V ±3%
(1.164V to 1.236V). Measure the output ripple voltage; it
should measure less than 20mV AC.
Set the input voltage to 12V and the output current to than
100mA. Observe the Burst Mode operation at the switch
node (the pad of the inductor opposite from the output),
and measure the output ripple voltage. It should measure
less than 100mV. Change the shunt position on the MODE
header from BM to PS (pulse-skipping mode) and observe
the voltage waveform at the switch pins. To achieve forced
continuous operation, insert two 100k resistors at the
pads for R1 and R2. These resistors develop a voltage of
INTV
CC
/2 at the MODE pin, which is the voltage setting
for forced continuous operation.
Insert the JP1 shunt into the OFF position and move the
shunt in the 1.2V output JP3 header into any of the re-
maining output voltage option headers: 1.8V (JP4), 2.5V
(JP5), 3.3V (JP6) or 5V (JP7). Just as in the 1.2V V
OUT
test, the output voltage should read V
OUT
±2% tolerance
under static line and load conditions and ±1% tolerance
under dynamic line and load conditions (±3% total). Also,
the circuit switch operation in Burst or pulse-skipping
mode operation will remain the same. There is an extra
output voltage header, JP8, to allow the user to easily set
the output to their desired value
When finished, turn off the circuit by inserting the shunt
in header JP1 into the OFF position.
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