Linear Technology LTC3542 User manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 993
500MA, 2.25 MHZ SYNCHRONOUS STEP-DOWN REGULATOR
1
LTC3542
DESCRIPTION
Demonstration circuit 993A is a step-down converter,
using the LTC3542 monolithic synchronous buck regula-
tor. The DC993A has an input voltage range of 2.5V to
5.5V, and is capable of delivering up to 500 mA of output
current in a small 2x2 mm DFN package. The output
voltage of the DC993A can be set as low as 0.6V, the
reference voltage of the LTC3542. At low load currents,
the DC993A can operate in either noise sensitive applica-
tions, due to the capability of the LTC3542 to operate in
pulse-skipping mode, or in high efficiency applications,
because the LTC3542 can also operate in Burst Mode.
Of course, in continuous mode, or large load current
applications, the DC993A is a high efficiency circuit -
over 90% in some cases. The DC993A consumes only
27 uA during sleep mode operation, and during shut-
down, it consumes at less than 1 uA. Because of the
high switching frequency of the LTC3542 – nominal 2.25
MHz - the DC993A uses low profile surface mount com-
ponents. These features, plus the LTC3542 coming in a
either a tiny 2x2 mm 6-Lead DFN package or a small 6-
Lead SOT package, make the DC993A an ideal circuit for
use in battery-powered, hand-held applications. Gerber
files for this circuit are available. Call the LTC Fac-
tory.
Table 1. Performance Summary (TA= 25°C)
PARAMETER CONDITIONS VALUE
Minimum Input Voltage 2.5V
Maximum Input Voltage 5.5V
GND = Shutdown
Run/Shutdown VIN = Run
1.2V ±4% (1.152V – 1.248V)
1.5V ±4% (1.44V - 1.56V)
Output Voltage VOUT
VIN = 2.5V to 5.5V, IOUT = 0A to 500 mA
1.8V ±4% (1.728V – 1.872V)
Typical Output Ripple VOUT VIN = 5V, IOUT = 500 mA (20 MHz BW) < 20mVP–P
Line ±1%
Output Regulation
Load ±1%
Nominal Switching Frequency 2.25 MHz
Burst Mode - VIN = 3.6V, VOUT = 1.8V ~60 mA ± 10 mA
Operation Modes
Pulse-Skip - VIN = 3.6V, VOUT = 1.8V ~60 mA ± 10 mA

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 993
500MA, 2.25 MHZ SYNCHRONOUS STEP-DOWN REGULATOR
2
QUICK START PROCEDURE
D emonstration Circuit 993 is easy to set up to evalu-
ate the performance of the LTC3542. For proper
measurement equipment configuration, set up the
circuit according to the diagram in Figure 1. Before
proceeding to test, insert shunts into the OFF position
of header JP3, which connects the RUN pin to ground
(GND), and thus, shuts down the circuit, and the 1.2V
output voltage header – JP4.
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 DC993 set up according to the proper meas-
urement and equipment in Figure 1, apply 3.3V 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. If de-
sired, one can measure the shutdown supply current
at this point. The supply current will be approxi-
mately 1 uA, or less, in shutdown.
Turn on the circuit by inserting the shunt in header
JP3 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 2.5V to 5.5V and adjust
the load current from 0 to 500 mA. Vout should read
between 1.2V +/- 4% (1.152V to 1.248V).
Measure the output ripple voltage at any output cur-
rent level; it usually will measure less than 30 mVAC.
Observe the voltage waveform at the switch node.
Verify the switching frequency is between 1.8 MHz
and 2.7 MHz (T = 0.555 us and 0.37 us), and that the
switch node waveform is rectangular in shape.
Insert header JP3 shunt into the OFF position and move
the 1.2V Vout shunt into any of the two remaining output
voltage option headers: 1.5V or 1.8V. Just as in the
1.2Vout 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).
When finished, turn off the circuit by inserting the
shunt in header JP3 into the OFF position (connecting
the RUN pin to ground).

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 993
500MA, 2.25 MHZ SYNCHRONOUS STEP-DOWN REGULATOR
3
Demonstration circuit 993 is a step-down converter based on the LTC3542 monolithic synchronous buck regulator.
The DC993 is easy to set up and evaluate the performance of the LTC3542. Refer to Figure 1 for proper equipment
set-up .
Figure 1. Proper Equipment Measurement Set-Up
Figure 2. Measuring Input or Output Ripple

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 993
500MA, 2.25 MHZ SYNCHRONOUS STEP-DOWN REGULATOR
4

Mouser Electronics
Authorized Distributor
Click to View Pricing, Inventory, Delivery & Lifecycle Information:
Analog Devices Inc.:
DC993A