QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 903A
STEP-UP /STEP-DOWN DC-DC CHARGE PUMP CONVERTER
1
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 assem-
bly 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 DC903A-
B 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 volt-
age. 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
(65
µ
A, no load). Also, the built-in soft-start limits in-
rush current at turn-on, and short-circuit current
limit/thermal protection help the part survive a continu-
ous short-circuit. All these features make the circuit ide-
ally suited for efficient DC-DC conversion in space-
constrained applications such as battery-powered hand-
held 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 (T
A
= 25°C)
PARAMETER CONDITION MINIMUM TYPICAL MAXIMUM
Input Voltage Range 1.8V 5.5V
Maximum Output Current DC903A-A, V
IN
≥
2.5V
DC903A-B, 1.8V < V
IN
< 5.5V 150mA
60mA
DC903A-A, V
IN
≥
2.5V, I
OUT
< 150mA
1.8V < V
IN
< 2.5V, I
OUT
<40mA 3.168V 3.3V 3.432V
Output Voltage V
OUT
DC903A-B, V
IN
> 1.8V, I
OUT
< 60mA 2.4V 2.5V 2.6V
DC903A-A, I
OUT
= 150mA 32mV
P–P
Output Ripple V
OUT
(20MHz BW)
DC903A-B, I
OUT
= 60mA 22mV
P–P
DC903A-A
−
1.7%
−
2.1%
Load Regulation
DC903A-B
−
0.6%
−
0.68%
Nominal Switching Frequency 1.2MHz
DC903A-A, V
IN
= 3.7V, I
OUT
= 150mA 85.8%
Efficiency
DC903A-B, V
IN
= 1.8V, I
OUT
= 60mA 69.4%
QUICK START PROCEDURE
1.
Demonstration circuit 903A is easy to set up to evalu-
ate 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:
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 903A
STEP-UP /STEP-DOWN DC-DC CHARGE PUMP CONVERTER
2
NOTE:
When 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.
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 ex-
ceed 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, ad-
just the loads within the operating range and observe
the output voltage regulation, ripple voltage, efficiency
and other parameters.
Figure 1.
Proper Measurement Equipment Setup
VIN
GND
Figure 2.
Measuring Input or Output Ripple
OPERATING PRINCIPLES
The LTC3240 is a step-up/step-down charge pump
DC/DC converter. For V
IN
greater than V
OUT
by about
100mV, the LTC3240 operates as a low dropout regula-
tor. Once V
IN
drops to within 100mV of regulated V
OUT
, the
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 903A
STEP-UP /STEP-DOWN DC-DC CHARGE PUMP CONVERTER
3
part automatically switches into charge pump step-up
mode to maintain the regulated output voltage. Regula-
tion 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 V
IN
on the first phase of the
clock. On the second phase of the clock it is stacked in
series with V
IN
and connected to V
OUT
.
Burst Mode operation, soft-start and short-circuit
/thermal protection can be found on the LTC3240 data-
sheet at www.linear.com.
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 903A
STEP-UP /STEP-DOWN DC-DC CHARGE PUMP CONVERTER
4
