QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 623
550KHZ MICROPOWER STEP-DOWN DC/DC CONTROLLER
LTC3801
DESCRIPTION
Demonstration circuit 623 is a step-down (buck)
regulator, using the LTC
®
3801 monolithic controller.
The DC623 has an input voltage range of 2.5V to 9.8V
and is capable of providing 1A at an output voltage of
2.5V from a single Li-Ion cell. The DC623 highlights
the capabilities of the LTC3801, a constant frequency
step-down DC-to-DC controller that comes in a tiny
SOT-23 package and runs off extremely low quiescent
currents. The LTC3801 uses a current mode PWM
architecture to drive an external P-channel power
Table 1.
PARAMETER
Minimum Input Voltage
Maximum Input Voltage
Output Voltage
Typical Output Ripple
Normal
Typical Supply Current
Sleep
Shutdown
Maximum Output Current
Typical Load Regulation
V
IN
= 2.5V to 9.8V, I
OUT
= 0A to 1A
V
IN
= 4.2V, I
OUT
= 600mA (20MHz BW)
V
IN
= 4.2V
V
IN
= 4.2V
V
IN
= 4.2V, lth/Run=0V
V
IN
= 4.2V, V
OUT
= 2.5V
V
IN
= 4.2V, 100mA
≤
I
OUT
≤ 1A
MOSFET in a buck regulator application. The result is
a high performance power supply that is ideal for cell
phones and other portable electronics operating from
one or two Li-ion cell. Due to the use of surface
mount components, the DC623 is a highly efficient
power supply for use in very small spaces.
Design files for this circuit board are available. Call the
LTC factory.
LTC is a registered trademark of Linear Technology Corporation.
Performance Summary (T
A
= 25°C)
CONDITION
VALUE
2.5V
9.8V
2.5V ±5%
100mV
P–P
195
16
5
1A (min)
1%
QUICK START PROCEDURE
Demonstration circuit 623 is easy to set up to evalu-
ate the performance of the LTC3801. Refer to
Figure 1 for proper measurement equipment setup
and follow the procedure below:
NOTE:
When measuring the input or output voltage
1.
Turn on the input power supply, set to 5V,
with no load on the output. Measure
V
OUT
; it should be 2.5V ±3% (2.425V to
2.575V).
2.
Vary the load current from no load to 1A.
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 V
IN
or V
OUT
and GND terminals.
See Figure 2 for proper scope probe technique.
The output voltage should be within a
tolerance of ±4% (2.4V and 2.6V).
3.
Vary the input voltage from 2.7V to 9.8V.
The output voltage should be within ±5%
tolerance (2.375V and 2.625V).
1
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 623
550KHZ MICROPOWER STEP-DOWN DC/DC CONTROLLER
4.
With the load current at 1A, measure the
6.
To shut down the circuit, connect the RUN
output ripple voltage; it should measure
less than 100 mVAC.
5.
Observe the voltage waveform at the
turret to ground (GND).
When finished, disconnect the power.
switch node (pin); the switching
frequency should be between 500kHz and
650kHz (T = 2 us and 1.5 us).
Figure 1. Proper Measurement Equipment Setup
Figure 2. Measuring Input or Output Ripple
VIN
GND
2
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