QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1105
LOW VIN SYNCHRONOUS STEP-DOWN CONVERTER WITH TRACKING
LTC3822EDD-1
DESCRIPTION
Demonstration circuit 1105A is a high efficiency syn-
chronous step-down DC/DC converter with output
tracking featuring the LTC3822EDD-1 controller. The
demo board is capable of providing 1.8V/8A from 2.75V
to 4.5V input. Burst mode/Pulse skipping/Forced
continuous operation is selectable. The constant
frequency current mode architecture with MOSFET V
DS
sensing eliminates the need for a sense resistor and
improves efficiency. The maximum peak current sense
threshold can easily be selected with the IPRG pin.
Switching frequency is internally set at 550KHz. The
frequency can be adjusted using PLLLPF pin. Tying
PLLLPF pin to GND selects 300KHz operation; tying
PLLLPF pin to V
IN
selects 750KHz operation. The switch-
ing frequency can also be externally synchronized from
250KHz to 750KHz using SYNC terminal (JP1 should be
selected for Sync).
The demo board has a tracking feature, allowing Vout to
track an external voltage signal at TRACK terminal (JP2
selected for Track).
Design files for this circuit board are available. Call
the LTC factory.
,
LTC and LT are registered trademarks of Linear Technology Corporation.
Table 1. Performance Summary (T
A
= 25°C)
PARAMETER
Input Voltage Range
V
OUT
Maximum load current I
OUT
Typical Output Ripple Voltage
Typical Switching Frequency
V
IN
= 2.75-4.5V, I
OUT
= 0A to 8A
V
IN
= 2.75-4.5V, V
OUT
= 1.8V
V
IN
= 3.3V, I
OUT
= 4A, Fs = 550KHz (20MHz BW)
PLLLPF Pin Floating
CONDITION
VALUE
2.75V to 4.5V
1.8V ±2%
8A
12mV
P–P
550kHz
QUICK START PROCEDURE
Demonstration circuit 1105A is easy to set up to evalu-
ate the performance of the LTC3822-1. Refer to Figure 1
for proper measurement equipment setup and follow the
procedure below: (Initial jumper positions: JP1: PS;
JP2: Soft Start)
measuring the input or output voltage rip-
ple, 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:
When
1.
2.
3.
4.
5.
With power off, connect the input power supply to
+Vin (2.75V-4.5V) and GND (input return).
Connect the 1.8V load between Vout and GND (Initial
load: 0 A).
Connect DVMs to the input and output.
Turn on the input power supply and check for the
proper output voltage. Vout should be 1.8V+/-2%.
Once the proper output voltage is established, adjust
the load within the operating range and observe the
1
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