Linear Technology 1060 User manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1060
DUAL MONOLITHIC STEP-DOWN SWITCHING REGULATOR
1
LT3508
DESCRIPTION
Demonstration circuit 1060 features two LT3508
step-down DC/DC switching converters. One circuit
uses the LT3508EFE and the other circuit has the
LT3508EUF. The LT3508 dual output step-down
switching regulator has two internal power
switches, a wide input voltage range, adjustable
switching frequency synchronizable over the fre-
quency range, programmable soft-start, tracking,
power-good, and channel sequencing. The anti-
phase switching reduces the input capacitor. The
wide V
IN
range of the LT3508 allows step-down
configurations with up to 36V input. The high power
internal switches have current limit that allows for
up to 1.4A output on each output.
The demonstration circuit has two circuits. The top
is optimized for high efficiency, wide input range
and maximum output current; the bottom is opti-
mized for the size. The top circuit is rated for 3.3V
at 1.4A and 5V at 1.4A output from a 6V–36V input
using the FE package. The frequency is set to
700kHz to allow for the high VIN to VOUT ratio and
provides high efficiency throughout the range. The
bottom circuit generates 1.8V at 1A and 3.3V at 1A
from a 5V to 16V DC input using the QFN package
and shows off the compact size with 1.6MHz
switching frequency. The two channels are se-
quenced so that the 1.8V channel starts before the
3.3V channel. The two circuits are completely iso-
lated from each other and can be run simultane-
ously or independently. The shutdown terminals are
available on each circuit as are the power good and
track terminals in case sequencing or tracking is
preferred.
This board is designed for applications that require
two step-down converters up to 1.4A load with low
cost, small board space, low parts count, and sim-
ple circuit design. The high current, on-board, dual
monolithic switches eliminate the need for external
switches. The current-mode control simplifies the
compensation network and gives excellent transient
response.
Please read the LT3508 datasheet in addition to this
quickstart guide for details regarding LT3508 opera-
tion and applications.
Design files for this circuit board are available.
Call the LTC factory.
LT is a trademark of Linear Technology Corporation

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1060
DUAL MONOLITHIC STEP-DOWN SWITCHING REGULATOR
2
TYPICAL PERFORMANCE (T
A
= 25°C)
60%
65%
70%
75%
80%
85%
90%
95%
100%
0 0.5 1 1.5
C H1, C H2 LO AD C URRE NT (mA )
E F F IC IE NC Y (%)
6V IN
18VIN
12VIN
3.3V, 5V
outputs
Figure 1. Typical Efficiency of DC1060A LT3508EFE Dual Step-
Down VOUT1=3.3V, VOUT2=5V
Table 1. FE package Dual Step-Down Converter (VOUT1=3.3V
and VOUT2=5V)
Parameter Value
V
IN
6V to 36V
V OUT1 3.3V
V
OUT
2 5V
V
OUT
1 Load Current 1.4A(max)
V
OUT
2 Load Current 1.4A(max)
Switching frequency 700kHz
V
OUT
1 Ripple pk-pk 25mV at 1.4A and 18VIN
V
OUT
2 Ripple pk-pk 18mV at 1.4A and 18VIN
Efficiency 86% at 1.4A load current (VOUT1
and VOUT2) and 12VIN
60%
65%
70%
75%
80%
85%
90%
95%
100%
0 0.25 0.5 0.75 1
C H1, C H2 LO A D C URRE NT (mA )
E F F IC IE N C Y (%)
5V IN
16VIN
12VIN
1.8V, 3.3V
outputs
Figure 2. Typical Efficiency of DC1060A LT3508EUF Dual Step-
Down VOUT1=1.8V, VOUT2=3.3V
Table 2. QFN Package Dual Step-Down Converter (VOUT1=1.8V
and VOUT2=3.3V)
Parameter Value
V
IN
5V to 16V
VOUT1 1.8V
VOUT2 3.3V
VOUT1 Load Current 1A(max)
VOUT2 Load Current 1A(max)
Switching frequency 1.6MHz
V
OUT
1 Ripple pk-pk 3mV at 1A and 12VIN
V
OUT
2 Ripple pk-pk 5mV at 1A and 12VIN
Efficiency 85% at 500mA load current
(VOUT1 and VOUT2) and 5VIN

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1060
DUAL MONOLITHIC STEP-DOWN SWITCHING REGULATOR
3
QUICK START PROCEDURE
DC1060A is easy to set up to evaluate the perform-
ance of the LT3508. Refer to Figure 3 for proper
measurement equipment setup and follow the proce-
dure below:
LT3508EFE top circuit:
1. Connect a 6V–36V DC input power supply to the
VIN and GND terminals on the board with power
OFF.
2. Attach the desired load to each channel – up to
1.4A.
3. After all connections are made, turn ON input
power and verify that the output voltages are 3.3V
and 5V.
4. The Track/SS, power good (PG), and shutdown
functions are optional and their terminals can be
left floating (disconnected). Connecting the shut-
down terminal to the GND terminal shuts down the
circuit and drops the output voltages to zero. Shut-
down has a pull-up resistor on circuit that may not
be necessary with the proper high and low signal
applied.
LT3508EUF bottom circuit
1. Use the same testing method for the bottom cir-
cuit as used in the top circuit, but with a different
input voltage (5V to 16V), load currents (1A per
channel maximum), and output voltages (1.8V
and 3.3V).
2. Upon startup, sequencing of VOUT1 and VOUT2
can be observed with an oscilloscope.
Figure 3. Proper Measurement Equipment Setup
SYNC FUNCTION
The Rt/Sync pin can be used for synchronization of the LT3508 internal oscillator to an external source. To use
the sync function, remove R2 (in the top FE circuit) or R13 (in the bottom UF circuit), and attach the external
sync signal to the Rt/Sync pin directly or to the now-unstuffed resistor pad tied to the Rt/Sync pin.

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1060
DUAL MONOLITHIC STEP-DOWN SWITCHING REGULATOR
4

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