DEMO CIRCUIT 1324A
PDC
QUICK START GUIDE
LTC3672BEDC-2: Monolithic
Fixed-Output 400mA Buck Regulator with Dual
150mA LDOs in 2mm X 2mm DFN
DESCRIPTION
Demonstration Circuit 1324A is a monolithic 400mA
Buck regulator, with fixed output, and two 150mA,
Low Drop Out linear regulators. These are housed in
an 8 lead, 2mm X 2mm DFN package.
Design files for this circuit board are available. Call
the LTC factory.
L
, LTC, LTM, LT, Burst Mode, OPTI-LOOP, Over-The-Top and PolyPhase are registered
trademarks of Linear Technology Corporation. Adaptive Power, C-Load, DirectSense, Easy
Drive, FilterCAD, Hot Swap, LinearView, μModule, Micropower SwitcherCAD, Multimode
Dimming, No Latency
ΔΣ,
No Latency Delta-Sigma, No R
SENSE
, Operational Filter, PanelProtect,
PowerPath, PowerSOT, SmartStart, SoftSpan, Stage Shedding, SwitcherCAD, ThinSOT,
UltraFast and VLDO are trademarks of Linear Technology Corporation. Other product names
may be trademarks of the companies that manufacture the products.
PERFORMANCE SUMMARY
Specifications are at T
A
= 25°C
SYMBOL
VIN
VOUT1
VOUT2
VOUT3
PARAMETER
Input voltage
Output of regulator (buck) 1
Output of LDO1
Output of LDO2
CONDITIONS
I
OUT1
≤ 400mA
I
OUT2
≤ 150mA. Subject to dropout limitations.
IOUT3 ≤ 150mA
MIN
2.9
1.17
2.73
1.755
TYP
MAX
5.5
1.23
2.87
1.845
UNITS
V
V
V
V
OPERATING PRINCIPLES
The LTC3672BEDC-2 is a monolithic fixed output,
400mA, synchronous buck regulator and two 150mA
LDOS.
Efficiency [%]
LTC3672BEDC-1
VOUT = 1.2V
100
90
80
70
60
50
40
30
20
0
100
200
300
400
LOAD CURRENT [mA]
VOUT1 is driven by a high efficiency synchronous buck
regulator with a fixed output of 1.2V. The buck regulator
on the LTC3672BEDC-2 operates at approximately
2.25MHz, allowing the use of small inductors and
capacitors.
The two fixed output LDOs, have a maximum dropout
voltage of 250mV, over process and temperature. This
allows all three outputs to remain in regulation with VIN
as low as 2.98V.
All of the regulators on the LTC3672BEDC-2 are enabled
via the ENALL pin, controlled by JP1.
Efficiency of the Buck regulator at VIN = 3.6V
1
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1324A
FIXED-OUTPUT 400MA BUCK REGULATOR WITH DUAL 150MA LDOS
LTC3672BEDC-2
AM1
+
+
VM2
-
+
LD1
0V-5V
-
-
VM3
-
-
AM2
+
1A
LD2
0V-5V
1A
+
+
PS1
0V-6V 2A Supply
-
-
VM1
-
-
+
+
+
VM4
AM3
+
+
-
-
LD3
0V-5V
1A
Figure 1: Test Equipment Hookup Diagram
1) Connect test equipment as shown in Figure 1.
Set PS1 = 0V, set PS1 Ilimit = 1A, set LD1 =
0A, LD2 = 0A, LD3 = 0A, and JP1 = ON.
2) Slowly increase PS1 and verify that all
regulators are operational at VIN ≥ 2.9V.
3) Set PS1 = 3.6V, and JP1 = ON. Verify VM2 =
1.17V~1.23V, VM3 = 1.755V ~ 1.845V, and
VM4 = 2.73V~2.87V.
4) Set PS1 = 2.9V, LD1 = 400mA. Verify VM2 =
1.17V~1.23V.
5) Set LD2 = 150mA, LD3=150mA. Verify that
VM3 = 1.755V~1.845V, and VM4 =
2.65~2.87V.
6) Set PS1 = 5.5V, and repeat step 5.
7) Set JP1 = OFF, set PS1 = 2.9V, verify that all
output voltages (VM2-4) are 0V.
8) Set PS1 = 5.5V, verify that all output voltages
(VM2-4) are 0V.
9) Set PS1 = 0V, set JP1 = ON.
2
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1324A
FIXED-OUTPUT 400MA BUCK REGULATOR WITH DUAL 150MA LDOS
LTC3672BEDC-2
Oscillograph 1:Startup from ENALL
Oscillograph 2:Shutdown from ENALL
Oscillograph 3:Startup from VIN
Oscillograph 4:Shutdown from VIN
3
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1324A
FIXED-OUTPUT 400MA BUCK REGULATOR WITH DUAL 150MA LDOS
LTC3672BEDC-2
APPLICATIONS INFORMATION
There are several components that are only necessary
under certain conditions. C1, C3, and R1, need to be
used as follows.
The connection of VIN to an operating supply may
have significant parasitic inductance. When this
connection is made to the DC1324A PCB, the supply
must charge up the local decoupling capacitance, C2.
A current is established in the connecting leads, while
this capacitor is charging. This current acts as a step
load to induce ringing in the connection. This ringing
may cause the voltage at VIN to rise to up to 2X the
supply voltage, possibly damaging devices, including
the LTC3672BEDC-2, on the DC1324A board. To
prevent this, the damping network composed of
C1&R1 has been added. R1 serves to reduce the Q of
the resonant circuit, and reduces overshoot on VIN
from resonant ringing. C1 blocks the DC voltage,
preventing R1 from consuming any DC current.
If the connection between VIN and the power supply is
very short, and has very low parasitic inductance, there
is no need for this damping circuit, and it may be
omitted.
This is usually the case when the
LTC3672BEDC-2 resides on the same PCB as the
source of the VIN voltage. Please be careful with
battery wiring that supplies VIN, as this may also have
significant parasitic inductance.
C3 provides a decoupling function, in the event that
some parasitic resistance and inductance exists
between VIN and VIN1. This impedance can be
problematic when the LTC3672BEDC-2 is supplying
current to loads that contain high speed transients. If,
in the application, a direct connection is made to VIN1,
then it is unlikely that C3 will be needed.
4
E1
VIN
1
2.9V - 5.5V
C1
10uF
0603
6.3V
R1
1.0
0402
LTC3672BEDC-2
U1
8
VIN
SW
1
E2
GND
C2
10uF
0603
6.3V
L1
4.7uH
EPL2014-472MLC
E10
VOUT1
1.2V
400mA
C6
10uF
0603
6.3V
E9
GND
5
VIN1
BUCKOUT
4
C3
2.2uF
6.3V
0402
OPT
LDO1
6
E8
VOUT2
2.8V
150mA
E7
GND
ON
3
ENALL
JP1
ENALL
OFF
C5
2.2uF
4V
0402
E3
GND1 GND
9
2
LDO2
7
E6
VOUT3
1.8V
150mA
E5
GND
C4
2.2uF
4V
0402
ENALL
Figure 2: Schematic of DC1324A: LTC3672BEDC-2 Monolithic Fixed-Ouput 400mA Buck Regulator with Dual
150mA LDOs in 2mm X 2mm DFN
GND
E4
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1324A
FIXED-OUTPUT 400MA BUCK REGULATOR WITH DUAL 150MA LDOS
LTC3672BEDC-2
Note1: Subject to the dropout limitations of LDO2 (VOUT3)
5
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