ADP3310 Analog Devices, ADP3310 Datasheet - Page 7

• Manufacturer Part Number: ADP3310
• Description: Precision Voltage Regulator Controller
• Manufacturer: Analog Devices

Current Limit Threshold Voltage = 0.05 V
Safety Factor = 1.5
I
R
In that case, the I
The simplest and cheapest sense resistor for high current applica-
tions, (i.e., Figure 1) is a PCB trace. The temperature depen-
dence of the copper trace and the thickness tolerances of the
trace must be taken into account in the design. The resistivity of
copper has a positive temperature coefficient of +0.39%/ C.
Copper’s Tempco in conjunction with the proportional-to-
absolute temperature (PTAT) current limit voltage can provide
an accurate current limit. Table II provides the resistance value
for PCB copper traces. Alternately, an appropriate sense resistor
such as surface mount sense resistors available from KRL can be
used.
PCB-Layout Issues
For optimum voltage regulation, place the load as close as pos-
sible to the device’s V
use dedicated PCB traces to connect the MOSFET’s drain to
the positive terminal and GND to the negative terminal of the
load to avoid voltage drops along the high current carrying PCB
traces.
Application Circuits
Typical 3 A LDO Circuit
The ADP3310 and a power MOSFET can be used to power the
new generation of CPUs and microprocessors from the standard
+5 V supply at a very low cost (Figure 14). This circuit provides
low dropout, fast switching and high switching load current
from 0 A to 3 A. Due to the high switching load current, capaci-
tors with high ripple current carrying capability, such as OSCON
or special tantalum capacitors from Sprague (593D), are recom-
mended for the output.
REV. A
O
S
= Output Current
is not needed in circuits that do not require current limiting.
22nF
1k
C
R
C
C
S
pin must be tied to the input pin.
470pF
OSCON
OUT
C
220 F
T
10nF
C2
and GND pins. It is recommended to
+
V
S-GND P-GND
INT V
SD
C T
C
I
IN
TH
IN
ADP1148
= 5V TO 15V
CC
V
N-DRIVE
P-DRIVE
IN
SENSE
SENSE
Figure 15. High Current Post Regulator with SOIC PMOS
FB
+
–
C1
1 F
IRF7204
N-CH
IRF7403
68µH
L*
** COILTRONICS CTX-68-4
** KRL SL-1-C1-ORO5OL
C3
1nF
R
D1
10BQ040
SENSE
0.1
**
OSCON
220 F
–7–
C4
2N3906
Conductor
Thickness
1/2 oz/ft
(18 m)
1 oz/ft
(35 m)
2 oz/ft
(70 m)
3 oz/ft
(106 m)
Figure 14. Typical 3 A Low Dropout Regulator Circuit
4.5V TO 5.5V
Q1
OSCON
R1
30.1k
1%
R2
124k
1%
220 F
2
2
2
2
Table II. Printed Circuit Copper Resistance
+
EN
IS
IN
ADP3310-3.3
10 F
1k
50mV/div
IRF7404
GATE
GND
MI
Conductor Width
In
0.025
0.050
0.100
0.200
0.500
0.025
0.050
0.100
0.200
0.500
0.025
0.050
0.100
0.200
0.500
0.025
0.050
0.100
0.200
0.500
0.011
2N3906
OUT
R2
V
EN
IN
ADP3310-3.3
Q2
IS
GND
2V/div
R3
274k
NDP6020P
GATE
M1
BAT54
V
OUT
10 F
C5
10 F
ADP3310
3.3V/1A
5 s/div
+
Resistance
m /In
39.3
19.7
9.83
4.91
1.97
19.7
9.83
4.91
2.46
0.98
9.83
4.91
2.46
1.23
0.49
6.5
3.25
1.63
0.81
0.325
3
OSCON
220 F
3.3V