DC741A - Demo Manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 741
DUAL OUTPUT LOW NOISE LDO REGULATORS
LTC3025
DESCRIPTION
Demonstration circuit 741 is an ultra-low dropout
voltage supply using the LTC3025 linear regulator,
which comes in a small 2mm x 2mm 6-Pin DFN
package. The DC741 has an input voltage range
from 0.9V to 5.5V, an output voltage range between 0.4V and 2.6V, and is capable of delivering
300 mA max of output current. The 0.4V reference
of the LTC3025 allows the DC741 to supply power
to very low voltage applications. DC741 is also an
excellent choice for post regulation of step-down
switching regulators, creating a high efficiency
low-noise supply. The DC741 comes assembled
with small ceramic capacitors, showing the
LTC3025 ability to maintain stability with ceramic
output capacitors.
Gerber files for this circuit are available. Call the LTC
Factory.
LTC is a trademark of Linear Technology Corporation.
QUICK START PROCEDURE
DC741 is easy to set up to evaluate the performance
of the LTC3025. For proper measurement equipment
configuration, set up the circuit according to the diagram in Figure 1.
4.
Insert jumper JP5 into the OFF position
and move the shunt from jumper JP2 into
any of the remaining output voltage options: 0.8V, 1.5V, or 1.8V. Re-insert jumper
JP5 into the ON position. Just as in the
1.2Vout test, the output voltage should
read Vout +/- 2% tolerance under static line
and load conditions, and +/- 2% tolerance
under dynamic line and load conditions.
5.
When finished evaluating, insert jumper
JP5 into the OFF position.
Please follow the procedure outlined below for
proper operation.
1.
2.
Before proceeding to test, insert jumper
JP5 into the OFF position, and insert a
shunt into jumper JP2 for 1.2V output.
Apply 1.3V to Vin (100 mV above Vout),
and 5V to Vbias.
Caution: The bias voltage must be 1.4V, or
greater, above the output voltage, and it
must be 2.5V, or greater, for the circuit to
regulate.
Insert jumper JP5 into the ON position.
Measure Vout; it should be 1.2V+/-2%
(1.176V to 1.224V).
3.
Vary the input voltage from 1.3V to 5.5V
and the load current from no load to 300
mA. Vout should measure 1.2V +/- 2%
(1.176V to 1.224V).
Note - If the power for the demo board is carried in
long leads, the input voltage at the part could
“ring”, due to the inductance in the long leads.
This ringing could affect the operation of the circuit
or even exceed the maximum voltage rating of the
IC. To eliminate the ringing, a small tantalum capacitor (for instance, an AVX part #
TAJW106M025R) was inserted on the pads between the input power and return terminals on the
bottom of the demo board. The (greater) ESR of
the tantalum will dampen the (possible) ringing
voltage due to the use of long input leads. On a
normal, typical PCB, with short traces, the capacitor is not needed.
1
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 741
DUAL OUTPUT LOW NOISE LDO REGULATORS
VBIAS must exceed Vout by 1.4V or greater
Figure1. Proper Measurement Equipment Setup
Figure 2. Measuring Input or Output Ripple
2
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 741
DUAL OUTPUT LOW NOISE LDO REGULATORS
RMS Output Noise vs. Load Current
(10 Hz to 100 kHz)
120
Vout - 1.8V
100
Output Noise (uVrms)
Vout - 1.5V
80
Vout - 1.2V
Vout - 0.8V
60
40
20
0
0
50
100
150
200
250
300
Load Current (mA)
Output Noise Spectral Density
Output Noise Spectral Density (uV/rootHz)
10
1
0.1
0.01
0.01
0.1
1
10
100
Frequency (kHz)
3
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 741
DUAL OUTPUT LOW NOISE LDO REGULATORS
10 Hz to 100 kHz Output Noise (X-Axis Scale: 1ms/div; Y-Axis Scale: 100uV/div)
LTC3025 Load-Step Response
4
A
B
C
D
E
4
4
3
3
VIN
1
BIAS
6
ENABLE
OUT
4
3
FB
5
GND
2
1
2
2
2
3
1
1
A
B
C
D
E
Item Qty Reference
1
2
3
4
5
6
7
8
9
10
11
12
13
14
3
1
0
0
6
4
1
2
3
2
1
1
1
2
C1,COUT,CIN
CIN1
COUT1 (Opt)
COUT2 (Opt)
E1,E2,E3,E4,E5,E6
JP1,JP2,JP3,JP4
JP5
XJP4,XJP5
R1,R2,R5
R3,R4
R6
U1
Part Description
Cap., X5R 1uF 6.3V 20%
Cap., Tant. 10uF 25V 20%
Cap., X5R 1uF 6.3V 20%
Cap., Tant. 100uF 10V 20%
Testpoint, Turret
Jumper, 2pins 2mm Ctrs.
Headers, 3 Pins 2mm Ctrs.
SHUNT, .079" CENTER
Res., Chip 40.2K 1/16W 1%
Res., Chip 30.1K 0.06W 1%
Res., Chip 10M 1/16W 5%
I.C., VLDO Linear Regulator
PRINTED CIRCUIT BOARD
STENCIL
Page 1 - of - 1
Manufacture / Part #
TDK C1005X5R0J105M
AVX TAJW106M025R
TDK C1005X5R0J105M
AVX TPSD107M010R0100
Mill Max 2501-2
CommConn Con Inc. 2802S-02G2
CommConn Con Inc. 2802S-03G2
CommConn Con Inc. CCIJ2MM-138GW
AAC CR05-4022FM
AAC CR05-3012FM
AAC CR05-106JM
Linear Tech. Corp. LTC3025EDC
DEMO CIRCUIT 741A
STENCIL DC741A
Similar pages