QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 912
BOOST AND INVERTING DC/DC CONVERTERS
1
LT3487EDD
DESCRIPTION
Demonstration circuit 912 features the LT
®
3487EDD.
The demo circuit demonstrates small size and low
component count in a Boost Circuit and an Inverting
Circuit. The Boost Converter is designed to convert a
3V-5V input to 15V output at 45mA-90mA maximum
load. The Inverting Circuit generates a -8V output at
90mA-150mA maximum load from the same input.
Since the maximum Vin of the LT3487EDD is 16V,
this Demo circuit will work well at higher inputs. The
only limitation is that the input has to be lower than
the Boost converter output (15V) in order to stay in
regulation. If Vin and VBAT will be powered sepa-
rately, cut trace as indicated on farside of board and
use “VBAT” pad on top.
The LT3487EDD features integrated Schottky diodes
for both outputs and requires only one resistor (per
output) to set the output voltage. Internal sequencing
disables switching on the negative supply until the
positive has reached 87% of its final value. Both cir-
cuits are designed to demonstrate the capacitor pro-
grammable Soft-Start feature with a single capacitor,
advantages of the 2MHz constant switching fre-
quency and the internal 32V switches. Both outputs
on this demo circuit can be modified for higher volt-
ages. These circuits are intended for space-conscious
applications such as CCD Bias, TFT LCD Bias, OLED
Bias and +/- Rail Generation for Op Amps.
Design files for this circuit board are available. Call
the LTC factory.
LT is a trademark of Linear Technology Corporation
Table 1.
Performance Summary (T
A
= 25°C)
PARAMETERS FOR 15V BOOST CIRCUIT CONDITION VALUE
Minimum Input Voltage 3V
Maximum Input Voltage 5V
Output Voltage V
OUT
V
IN
= 3V, I
OUT
= 0mA to 45mA 15V ±5%
Output Voltage V
OUT
V
IN
= 5V, I
OUT
= 0mA to 90mA 15V ±5%
Maximum Output Current Vin = 3V 45mA
Maximum Output Current Vin = 5V 90mA
Typical Output Ripple V
OUT
V
IN
= 3.3V, I
OUT
= 45mA 20mV
P–P
Typical Efficiency V
IN
= 3.6V, Vout = 15V@45mA 77%
PARAMETERS FOR -8V INVERTING CIRCUIT VALUE
Output Voltage V
OUT
V
IN
= 3V, I
OUT
= 0mA to 90mA -8V ±5%
Output Voltage V
OUT
V
IN
= 5V, I
OUT
= 0mA to 150mA -8V ±5%
Maximum Output Current Vin = 3V 90mA
Maximum Output Current Vin = 5V 150mA
Typical Output Ripple V
OUT
V
IN
= 3.6V, I
OUT
= 100mA 10mV
P–P
Typical Efficiency V
IN
= 3.6V, Vout = -8V@100mA 70%
