DC903A - Demo Manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 903A
STEP-UP /STEP-DOWN DC-DC CHARGE PUMP CONVERTER
LTC3240-3.3 and LTC3240-2.5
DESCRIPTION
Demonstration circuit 903A is a step-up/step-down
charge pump dc-dc converter. It comes with two assembly versions, DC903A-A and DC903A-B featuring the
LTC3240-3.3 and LTC3240-2.5 respectively, each in a
tiny 2mmx2mm DFN package.
The DC903A-A and DC903A-B generate a fixed regulated
output of 3.3V and 2.5V respectively over a wide input
voltage range from 1.8V to 5.5V. The output current can
reach up to 150mA when the input voltage is above 2.5V
in DC903A-A. The maximum output current of DC903AB is designed at 60mA over the full input range.
The DC903A optimizes the output efficiency by operating
in the LDO step-down mode during most of the battery
life time when the input is higher than the output voltage. When the battery voltage gets low enough it auto-
matically switches into charge-pump doubling mode to
maximize the battery usage.
Additionally, DC903A features Automatic Burst Mode
operation at light load to achieve low supply current
(65µA, no load). Also, the built-in soft-start limits inrush current at turn-on, and short-circuit current
limit/thermal protection help the part survive a continuous short-circuit. All these features make the circuit ideally suited for efficient DC-DC conversion in spaceconstrained applications such as battery-powered handheld electronics.
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
CONDITION
MINIMUM
Input Voltage Range
Maximum Output Current
Output Voltage VOUT
150mA
DC903A-B, 1.8V < VIN < 5.5V
60mA
DC903A-A,
Load Regulation
(20MHz BW)
VIN ≥ 2.5V, IOUT < 150mA
1.8V < VIN < 2.5V, IOUT <40mA
VIN > 1.8V, IOUT < 60mA
3.168V
3.3V
3.432V
2.4V
2.5V
2.6V
DC903A-A, IOUT = 150mA
32mVP–P
DC903A-B, IOUT = 60mA
22mVP–P
DC903A-A
−1.7%
−2.1%
DC903A-B
−0.6%
−0.68%
Nominal Switching Frequency
Efficiency
MAXIMUM
5.5V
DC903A-A, VIN ≥ 2.5V
DC903A-B,
Output Ripple VOUT
TYPICAL
1.8V
1.2MHz
DC903A-A, VIN = 3.7V, IOUT = 150mA
85.8%
DC903A-B, VIN = 1.8V, IOUT = 60mA
69.4%
QUICK START PROCEDURE
1.
Demonstration circuit 903A is easy to set up to evaluate the performance of the LTC3240-3.3 and
LTC3240-2.5.
Refer to Figure 1 for proper measurement equipment
setup and follow the procedure below:
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 903A
STEP-UP /STEP-DOWN DC-DC CHARGE PUMP CONVERTER
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.
2.
Place JP1 jumper in the ON position.
3.
With power off, connect a 1.8V-5.5V, 500mA power
supply to Vin and GND.
4.
Connect a load (preset load current to 0A) to Vout and
GND.
5.
Turn on the power at the input.
NOTE: Make sure that the input voltage does not exceed 5.5V.
6.
Check for the proper output voltages. Vout should
measure a typical 3.3V (could vary from 3.168V to
3.432V) for DC903A-A, and a typical 2.5V (could vary
from 2.4V to 2.6V) for DC903A-B.
7.
Once the proper output voltages are established, adjust the loads within the operating range and observe
the output voltage regulation, ripple voltage, efficiency
and other parameters.
Figure 1. Proper Measurement Equipment Setup
GND
VIN
Figure 2. Measuring Input or Output Ripple
OPERATING PRINCIPLES
The LTC3240 is a step-up/step-down charge pump
DC/DC converter. For VIN greater than VOUT by about
100mV, the LTC3240 operates as a low dropout regulator. Once VIN drops to within 100mV of regulated VOUT, the
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 903A
STEP-UP /STEP-DOWN DC-DC CHARGE PUMP CONVERTER
part automatically switches into charge pump step-up
mode to maintain the regulated output voltage. Regulation is achieved by sensing the output voltage through
an internal resistor divider and modulating the charge
pump output current based on the feedback error signal.
In the charge pump mode, a 2-phase non-overlapping
clock activates the charge pump switches. The flying
capacitor is charged from VIN on the first phase of the
clock. On the second phase of the clock it is stacked in
series with VIN and connected to VOUT.
Burst Mode operation, soft-start and short-circuit
/thermal protection can be found on the LTC3240 datasheet at www.linear.com.
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 903A
STEP-UP /STEP-DOWN DC-DC CHARGE PUMP CONVERTER
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