QUICK START GUIDE FO
R DEMONSTRATION CIRC
UIT 1389A
1
DESCRIPTION
Demonstration circuit 1389A is high efficiency triple out-
put DC/DC power supply featuring the LTC3521. The IC
includes a 4-switch synchronous Buck-Boost DC/DC
converter with 1A switch ratings and two synchronous
600mA Buck converters. The board will accept an input
voltage between 2.4V and 5V, and provide fixed output
voltages of 3.3V @800mA for the Buck-Boost converter
and 1.2V & 1.8V @600mA for the Buck converters.
The board includes jumpers for shutdown for each con-
verter, one jumper for PWM or BURST operation and
terminals to monitor each converter’s Power Good out-
put signal. Other features are; 1µA shutdown current,
integrated soft start, thermal and over current protection,
under voltage lockout, 100% duty cycle for the Buck
converter and a 1MHz switching frequency that allows
small L and C components to be used.
With BURST mode selected, the buck converters operate
in BURST mode at low load current and automatically
switch to PWM mode at higher loads. The Buck-Boost
converter will also operate in burst mode but the avail-
able load current is reduced considerably, to approxi-
mately 50mA. No load BURST mode quiescent current is
approximately 50µA. When all three converters are shut-
down, the quiescent current drops to less than 1µA.
The Power Good output terminals pull low if the output
voltage is 8% or more below the regulation voltage.
The LTC3521 datasheet gives a complete description of
the part, operation and application information. The data-
sheet must be read in conjunction with this quick start
guide.
Design files for this circuit board are available. Call
the LTC factory.
, LTC and LT are registered trademarks of Linear Technology Corporation. ThinSOT and
PowerPath are trademarks of Linear Technology Corporation.
Performance Summary ( TA = 25oC )
PARAMETER CONDITION VALUE
Input Voltage Range 2.4V to 5V
Buck-Boost Output Voltage (Vout 1) Vin = 2.4V, Vout Load = 100mA 3.3V
+/- 2.5%
Buck Output Voltage (Vout 2) Vin = 2.4V, Vout Load = 100mA 1.2V
+/- 2.5%
Buck Output Voltage (Vout 3) Vin = 2.4V, Vout Load = 100mA 1.8V
+/- 2.5%
Maximum Output Current (Buck-Boost) Vin = 2.4V, PWM mode 800mA
Maximum Output Current (Buck) Vin = 2.4V 600mA
Input Supply Current All Converters Shutdown, Vin = 2.4V <1µA
Input Supply Current (no load) All Converters Enabled, BURST Mode, Vin = 2.4V, No Load 50µA, typ.
Input Supply Current (no load) All Converters Enabled, PWM Mode, Vin = 2.4V, No Load 8.5mA, typ.
Table 1. Circuit Specifications
QUICK START PROCEDURE
This Demonstration circuit 1389A can be evaluated using the setup
shown in Figure 1.
1.
Place all Shutdown jumpers in the ON position and the
MODE jumper to the PWM position.
DEMO CIRCUIT 1389A
QUICK START GUIDE
LTC3521EUF
Synchronous 1A Buck-
Boost DC/DC Converter and
Dual 600mA Buck DC/DC Converters
QUICK START GUIDE FO
R DEMONSTRATION CIRC
UIT 1389A
2
2.
With AC power off, connect the input power supply to Vin and
GND.
3.
Connect voltmeters to Vin and ground terminals and each
Vout and Ground terminals.
4.
With the input voltage turned down, switch on the input power
supply and raise the input voltage to 1.8V.
5.
Verify that each output voltage meets the values as shown in
Table 1.
6.
Increase the input voltage to 2.5V and connect suitable load
resistors between each output and ground.
7.
Verify each output voltage. If an output is low, temporarily dis-
connect the load to make sure that the load current is not set
too high. Also, monitor the input voltage at the board terminals
to verify that the input voltage has not dropped due to the in-
creased input current. Note: The Buck-Boost converter output
current is limited to approximately 50mA if the Mode jumper is
set for BURST.
8.
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.
9.
The Power Good terminals can be monitored with a voltmeter
or an oscilloscope. The Power Good outputs pull low if the
output voltage is 8% or more below the regulation voltage,
otherwise they are pulled up to their respective output voltage
through a 1MΩ pull-up resistor.
10.
To measure no load input current, connect a mA/µA meter in
series with the input supply, adjust for 2.4V and read meter.
Both BURST and PWM quiescent current can be verified by
moving JP1 to the appropriate position.
RL2
+
+
+
+
-
-
-
-
V
out
2
RL2
V
out
3
V
out
1
RL1
Power
Supply
Power
Good
Outputs
Mode
Shutdown
Figure 1.
Proper Measurement Equipment Setup
Figure 2.
Measuring Input or Output Voltage Ripple
QUICK START GUIDE FO
R DEMONSTRATION CIRC
UIT 1389A
3
+
CIN1
47uF
10V
C9
(Opt)
C10
(Opt)
JP4
ON
OFF
SHDN31
3
2
R1
1M
R2
1M
R3
1M
PGOOD1
PGOOD2
PGOOD3
JP2
ON
OFF
SHDN11
3
2
JP3
ON
OFF
SHDN21
3
2
C3
22uF
6.3V
1206
E4
GND
VOUT1
VOUT3
VOUT2
E1
VIN
2.4V - 5V
E3
VOUT1
3.3V / 1A
E2
GND
U1
LTC3521EUF
SW3
17
F B1
8
PGN D1A
21
F B3
23
SW1A
15
VIN
5
PVIN1
11
SW1B
14
PGO O D2
3
PGO O D1
4
S H DN 2
1
S H DN 1
10
GND
6
PGN D1B
12
PGN D2
18
PWM
7
S H DN 3
9
PGO O D3
2
V O U T1
16
PVIN2
22
SW2
20
F B2
24
GND
25
R9
100K
1%
R8
102K
1%
C4
22pF
L3
3.3uH
Sumida
CDRH2D18/HP-3R3NC
R4
1.00M
1%
L2
3.3uH
Sumida
CDRH2D18/HP-3R3NC
C1
22pF
R7
68.1K
1%
R6
137K
1%
VOUT2 E5
VOUT2
1.8V / 600mA
E6
GND
C2
10uF
6.3V
0805
PGOOD1
PGOOD3
PGOOD2
R5
221K
1%
E9
PGOOD1
E7 VOUT3
1.2V / 600mA
E8
GND
C5
10uF
6.3V
0805
E10
PGOOD2
E11
PGOOD3
VOUT3
JP1
PWM
BURST
MODE
1
3
2
VIN
C6
0.1uF
C7
0.1uF
CIN4
4.7uF
10V
C8
0.1uF
VOUT1
L1
4.7uH
CDRH5D16NP-4R7NC
Sumida
CIN2
4.7uF
10V
CIN3
4.7uF
10V