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:
