DC822A - Demo Manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 822
DUAL SYNCHRONOUS, 800MA/400MA, 2.25 MHZ STEP-DOWN DC/DC REGULATOR
LTC3548
DESCRIPTION
Demonstration circuit DC822 is a Dual channel Synchronous, 2.25MHz Step-Down DC/DC Regulator featuring the LTC 3548. The DC822 has an input voltage range of 2.5V to 5.5V. The 2.5V output is capable
of delivering up to 400mA of output current; The
jumper selective 1.2V/1.5V/1.8V output is capable of
delivering up to 800mA of current. In Burst Mode
operation, the LTC3548 requires only 40uA of quiescent current, as a result, the DC822 provides good
efficiency at light load currents. In Pulse Skip mode,
the DC822 provides lower output ripple voltage at
light load currents than in Burst Mode. In either
mode, the DC822 can provide up to 95% efficiency
and consumes less than 1uA in shutdown. The
LTC3548 comes in a small 10-Pin DFN package,
which has an exposed pad on the bottom-side of the
IC for good thermal performance. These features,
plus the nominal operating frequency of 2.25MHz (allowing the exclusive use of low profile surface mount
components), make the DC822 demo board an ideal
reference circuit for battery-powered, hand-held
applications.
Design files for this circuit board are available. Call
the LTC factory.
LTC is a trademark of Linear Technology Corporation
Table 1. Performance Summary (TA = 25°C)
PARAMETER
Minimum Input Voltage
CONDITION
Maximum Input Voltage
VALUE
2.5V
5.5V
1.2V ±2%
Output Voltage VOUT1
VIN = 2.5V to 5.5V, IOUT1 = 0A to 800mA
1.5V ±2%
1.8V ±2%
Typical Output Ripple VOUT1
VIN = 5V, IOUT1 = 800mA (20MHz BW)
20mVP–P
Line
±1%
Load
±1%
Output Voltage VOUT2
VIN = 2.5V to 5.5V, IOUT2 = 0A to 800mA
2.5V ±2%
Typical Output Ripple VOUT2
VIN = 5V, IOUT2 = 400mA (20MHz BW)
20mVP–P
Line
±1%
Load
±1%
Output Regulation
Output Regulation
Nominal Switching Frequency
2.25MHz
1
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 822
DUAL SYNCHRONOUS, 800MA/400MA, 2.25 MHZ STEP-DOWN DC/DC REGULATOR
QUICK START PROCEDURE
Demonstration circuit 822 is easy to set up to evaluate the performance of the LTC3548. Refer to Figure 1
for proper measurement equipment setup and follow
the procedure below.
Note: 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 technique.
Note: The POR pin is an open-drain output which
pulls low when either regulator is out of regulation.
When both output voltages are within ---8.5% of regulation, a timer is started which releases POR after 218
clock cycles. This delay can be significantly longer in
Burst Mode operation with low load currents, since
the clock cycles only occur during a burst and there
could be milliseconds of time between bursts. This
can be bypassed by tying the POR output to the
MODE/SYNC input to force pulse skipping mode during a reset (JP4 needs to be removed when connecting POR to MODE/SYNC).
1.
Connect the input power supply to the Vin and
GND terminals on the left-side of the board. Do
not hot-plug Vin or increase Vin over the rated
maximum supply voltage of 5.5V. Connect the
loads between the Vout and GND terminals on the
right-side of the board. Refer to Figure 1 for the
proper measurement equipment setup.
2.
Before proceeding to operation, insert jumpers JP1
and JP2 into the OFF positions, jumper JP3 into
the Vout1 voltage position of choice (1.2V, 1.5V,
and 1.8V), and jumper JP4 into the desired mode
of operation: Pulse Skip or Burst Mode.
3.
Apply 3.3V at Vin. Measure both Vouts; they
should read 0V. The supply current will be approximately 33uA in shutdown, with roughly 32uA
due to the optional 100kΩ pull-up resistor of the
Power-On Reset (POR) feature. This resistor can
be removed to measure the actual shutdown supply current (of approx. 1uA).
4.
Turn on Vout1 and Vout2 by changing jumpers JP1
and JP2 from the OFF position(s) to the ON position(s). Vary the input voltage from 2.5V to 5.5V
and adjust each load current from 0 to full load.
Both output voltages should be regulating. The
regulated error is less than 2% of rated voltage.
5.
Set the load current of outputs between 25% to
100% load range, and measure both output ripple
voltages; they should measure less than 20mV
each. The switching frequencies should be between
1.8MHz and 2.7MHz (T = 0.555 us and 0.37 us)
2
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 822
DUAL SYNCHRONOUS, 800MA/400MA, 2.25 MHZ STEP-DOWN DC/DC REGULATOR
V
+
+
Load
+
A
Power
supply
V
+
+
V
Load
+
A
A
+
Figure 1. Proper Measurement Equipment Setup
Figure 2. Scope Probe Placement for Measuring Input or Output Ripple
3
+
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 822
DUAL SYNCHRONOUS, 800MA/400MA, 2.25 MHZ STEP-DOWN DC/DC REGULATOR
4
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