DEMO BOARD MANUAL DC324
LTC1876 High Efficiency, Low Cost, 3-Output Power Supply
DESCRIPTION
Demonstration Board DC324 is a high efficiency, low cost design using the LTC
®
1876.
This demo board provides three regulated outputs from a single IC: 3.3V/5A, 5V/5A and
12V/200mA, along with two LDO outputs at 3.3V and 5V. Using only a small number of
surface mount components, this design is ideal for network equipment, notebook
computers and other portable applications that require low profile, small board area and
minimum system cost. High efficiency and low EMI are also achieved by operating the
two main power stages 180° out of phase, which, in turn, results in long battery life and
smaller input capacitors. All three main outputs can be adjusted externally and the 12V
regulator is configured to receive its input from the 3.3V output, the 5V output or an
external supply.
DC324 highlights the capabilities of the LTC1876, which incorporates a dual out-of-
phase, step-down switching controller and a step-up regulator with an internal 1A, 36V
switch. It uses a constant frequency, current mode architecture to provide excellent line
and load regulation for all three outputs. The operating frequency of the step-down
controller is DC programmable from 150kHz to 300kHz and the frequency of the step-up
regulator is fixed at 1.2MHz, allowing the use of tiny, low cost capacitors and inductors.
Protection features of the controller include an overvoltage soft latch, an overcurrent
latch-off (which can be externally defeated) and internal current foldback for overload
situations. At low output currents, two modes of operation are available: Burst Mode™
operation to maintain high efficiency and burst disable mode to maintain constant
frequency operation. The controller is also capable of very low dropout operation, with a
99% maximum duty cycle. To be compatible with battery operation, the input range of
this demo board is 7.5V to 24V for the 3.3V and 5V outputs and from 3V to10V for the
12V output.
Gerber files for this circuit board are available. Call the LTC factory.
PERFORMANCE SUMMARY (Operating Temperature Range: 0°C to 50°C)
PARAMETERS
Input Voltages
CONDITIONS
Step-Down Channels (V
OUT
= 5V and 3.3V); Limited by
External MOSFET Drive and Breakdown Requirement
Step-Up Channel (V
OUT
= 12V)
Step-Down Channel 1; Externally Adjustable
Step-Down Channel 2; Externally Adjustable
Step-Up Channel; Externally Adjustable
5V Linear Regulator
3.3V Linear Regulator
Step-Down Channels
V
IN2
= 3.3V
Step-Up Channel
V
IN2
= 10V
VALUE
5.2V to 30V
2.6V to 11V
5.00V
±
0.10V
3.30V
±
0.07V
12.00V
±
0.24V
5.00V
±
4%
3.30V
±
4%
0 to 5A, 6A Peak
200mA
600mA
Output Voltages
Load Currents
PARAMETERS
Frequencies
Output Ripple Voltages
Line Regulation
Load Regulation
Supply Current
Shutdown Current
Standby Current
Efficiency
CONDITIONS
Step-Down Channels; Externally Adjustable; FREQSET Pin
Tied to INTV
CC
Step-Up Channel; Fixed
Step-Down Channel 1; 20MHz BW; V
IN
= 15V; I
O
= 5A
Step-Down Channel 2; 20MHz BW; V
IN
= 15V; I
O
= 5A
Step-Up Channel; 20MHz BW; V
IN2
= 5V; I
O
= 200mA
Step-Down Channel 1; V
IN
= 7.5V to 24V
Step-Down Channel 2; V
IN
= 7.5V to 24V
Step-Up Channel; V
IN
= 3.3V to 10V
Step-Down Channel 1; V
IN
= 15V; V
OUT1
= 5.00V; I
O
= 0 to 5A
Step-Down Channel 2; V
IN
= 15V; V
OUT2
= 3.30V; I
O
= 0 to 5A
Step-Up Channel; V
IN
= 5V; V
OUT3
= 12.00V; I
O
= 0 to 200mA
V
IN
= 15V; All Three Channels On; EXTV
CC
= V
OUT1
V
IN
= 15V; STBYMD = 0
V
IN
= 15V; 1MΩ Resistor from STBYBD to V
IN
; 5V INTV
CC
and
3.3V LDO On; RUN/SS1 = RUN/SS2 = AUXSD = 0
V
IN
= 15V; V
IN2
= V
OUT1
; 4A Load at 5V Channel (Not Including
the Supply Current to 12V Channel); 5A Load at 3.3V
Channel; 200mA at 12V Channel
VALUE
300kHz
1.2MHz
60mV
P-P
60mV
P-P
50mV
P-P
±5mV
±5mV
±5mV
−60mV
−60mV
−10mV
80µA*
20µA
170µA
90%
*400µA including the supply current from EXTV
CC
. Dynamic supply current is higher
due to the gate charge being delivered at the switching frequency. See the LTC1876 data
sheet for more information.
TYPICAL PERFORMANCE CHARACTERISTICS
1; 5V Channel
Vin(V)
15
15
15
15
15
15
15
15
15
15
(Both 3.3V and 12V Channels are
Iin(A)
Vout(V)
Iout(A)
0.004
5.02
0
0.01
5.01
0.015
0.023
5
0.052
0.041
4.99
0.102
0.182
4.99
0.496
0.356
4.98
1.004
0.706
4.98
2.003
1.066
4.98
3.002
1.44
4.98
4.002
1.822
4.97
4.99
OFF)
Eff.(%)
0
50.1
75.36232
82.76098
90.66081
93.63146
94.19207
93.49568
92.26833
90.74387
2; 3.3V Channel
(Both 5V and 12V Channels are OFF)
Vin(V)
Iin(A)
Vout(V)
Iout(A)
Eff.(%)
15
0.004
3.38
0
0
15
0.008
3.37
0.014
39.31667
15
0.017
3.356
0.051
67.12
15
0.03
3.346
0.102
75.84267
15
0.131
3.339
0.505
85.81145
15
0.251
3.337
1.004
88.98667
15
0.488
3.335
2.003
91.2569
15
0.735
3.334
3.002
90.78157
15
0.995
3.329
4.001
89.24174
15
1.264
3.32
4.99
87.37764
3; 12V Channel
(Both 5V and 3.3V Channels are
Vin(V)
Iin(mA)
Vout(V) Iout(mA)
5
6
11.96
0
5
46
11.97
14
5
145
11.95
51
5
280
11.94
101
5
336
11.94
122
5
392
11.94
142
5
452
11.94
163
5
502
11.94
181
5
563
11.94
201
OFF)
Eff.(%)
0
72.86087
84.06207
86.13857
86.70714
86.50408
86.11593
86.1012
85.25542
100
95
90
85
80
75
70
65
60
55
50
0.01
0.1
Load Current (A)
1
Vin=15V
Efficiency of 3.3V
Efficiency of 5V
10
90
85
80
75
70
65
60
55
50
10
100
Load Current (mA)
1000
Vin2=5V
Efficiency of 12V
MEASUREMENT SETUP
The circuit shown in Figure 1 provides three fixed voltages: 5V, 3.3V and 12V, at
currents of up to 5A, 5A and 200mA, respectively. Figure 2 illustrates the correct
measurement setup to be used to verify the typical numbers found in the Performance
Summary table. Small spring clip leads are very convenient for small-signal bench testing
but should not be used at the current and impedance levels associated with this switching
regulator. Soldered wire connections are requited to properly ascertain the performance
of this demonstration board. Do not tie the grounds together off the test board.
The six jumpers on the left side of the board are settable as follows: the center pin is
connected to ground when the jumper is in the rightmost position. The center pin is
connected to a positive bias source when the jumper is in the leftmost position. The
jumper below L2 at the lower right side of the board is used to select the input supply for
the step-up channel.
V
OUT
2
(3.3V) is selected if this jumper is in the leftmost position and
V
OUT
1
(5V) is selected if it is in the rightmost position. This jumper should be left off
when a separate power supply is used through the
V
IN
2
terminal near the jumper. Refer to
the Jumper Configuration table for jumper functions.
QUICK START GUIDE
This demonstration board is easily set up to evaluate the performance of the LTC1876.
Please follow the procedure outlined below for proper operation.
LOAD
LTC1876CG
DEMO CIRCUIT 324A
HIGH EFFICIENCY
LOW COST 3-OUTPUT
POWER SUPPLY
GND
PGOOD
5V/5A
GND
INTVCC
RUN/SS
FREQ
STDBY
FCB
3.3V
VIN
+
–
RUN/SS2
AUXSD 12V/O.2A GND
3.3V/5A
VOUT1
VIN2
VOUT2
VIN2
LOAD
LOAD
Figure 2. DC324A Test and Measurement Setup
1. Refer to Figure 2 for board orientation and proper measurement equipment setup.
2. Place the jumpers as shown in the diagram. Temporarily leave the STDBY jumper
off.
3. Connect the desired loads between
V
OUT
1
,
V
OUT
2
and
V
OUT
3
and their closest GND
terminals on the board. The loads can be up to 5A for
V
OUT
1
and
V
OUT
2
and 200mA
for
V
OUT
3
. Soldered wires should be used when load current exceeds 1A in order to
achieve optimum performance.
4. Connect the input power supply to the
V
IN
and GND terminals on the right edge of
the board. Do not increase
V
IN
over 30V or the MOSFETs may be damaged. The
recommended
V
IN
to start is <7V.
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