ADP1111-5 View Datasheet(PDF) - Analog Devices
Part Name
Description
Manufacturer
ADP1111-5
Analog Devices
ADP1111-5 Datasheet PDF : 16 Pages
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ADP1111
Table I. Component Selection for Typical Converters
Input Output Output
Circuit Inductor Inductor
Voltage Voltage Current (mA) Figure Value
Part No.
2 to 3.1 5
2 to 3.1 5
2 to 3.1 12
2 to 3.1 12
5
12
5
12
6.5 to 11 5
12 to 20 5
20 to 30 5
5
–5
12
–5
90 mA
10 mA
30 mA
10 mA
90 MA
30 mA
50 mA
300 mA
300 mA
7 mA
250 mA
4
15 µH
CD75-150K
4
47 µH
CTX50-1
4
15 µH
CD75-150K
4
47 µH
CTX50-1
4
33 µH
CD75-330K
4
47 µH
CTX50-1
5
15 µH
5
56 µH
CTX50-4
5
120 µH CTX100-4
6
56 µH
CTX50-4
6
120 µH CTX100-4
NOTES
CD = Sumida.
CTX = Coiltronics.
**Add 47 Ω from ILIM to VIN.
**Add 220 Ω from ILIM to VIN.
Capacitor
Value
33 µF
10 µF
22 µF
10 µF
22 µF
15 µF
47 µF
47 µF
47 µF
47 µF
100 µF
Notes
*
**
**
**
**
POSITIVE-TO-NEGATIVE CONVERSION
The ADP1111 can convert a positive input voltage to a negative
output voltage as shown in Figure 22. This circuit is essentially
identical to the step-down application of Figure 19, except that
the “output” side of the inductor is connected to power ground.
When the ADP1111’s internal power switch turns off, current
flowing in the inductor forces the output (–VOUT) to a negative
potential. The ADP1111 will continue to turn the switch on
until its FB pin is 1.25 V above its GND pin, so the output
voltage is determined by the formula:
VOUT
= 1.25 V
•
1
+
R2
R1
INPUT
+
CINPUT
RLIM
123
ILIM VIN SW1
SW2 4
ADP1111
AO
SET
FB
GND
8
67
NC NC
5
D1
1N5818
L1
R2
OUTPUT
+
R1
CL
NEGATIVE
OUTPUT
also reduces the circuit’s output voltage sensitivity to tempera-
ture, which otherwise would be dominated by the –2 mV VBE
contribution of Q1. The output voltage for this circuit is
determined by the formula:
VOUT
= 1.25 V • R2
R1
Unlike the positive step-up converter, the negative-to-positive
converter’s output voltage can be either higher or lower than the
input voltage.
L1
RLIM
+
C2
1
2
ILIM VIN
SW1 3
ADP1111
FB 8
AO SET GND SW2
6 754
D1
1N5818
R2
Q1
MJE210
+
D2
2N3906
POSITIVE
OUTPUT
CL
10kΩ
R1
NEGATIVE
INPUT
NC NC
Figure 23. ADP1111 Negative-to-Positive Converter
Figure 22. Positive-to-Negative Converter
The design criteria for the step-down application also apply to
the positive-to-negative converter. The output voltage should be
limited to |6.2 V| unless a diode is inserted in series with the
SW2 pin (see Figure 20.) Also, D1 must again be a Schottky
diode to prevent excessive power dissipation in the ADP1111.
NEGATIVE-TO-POSITIVE CONVERSION
The circuit of Figure 23 converts a negative input voltage to a
positive output voltage. Operation of this circuit configuration is
similar to the step-up topology of Figure 18, except the current
through feedback resistor R2 is level-shifted below ground by a
PNP transistor. The voltage across R2 is VOUT –VBEQ1. How-
ever, diode D2 level-shifts the base of Q1 about 0.6 V below
ground thereby cancelling the VBE of Q1. The addition of D2
LIMITING THE SWITCH CURRENT
The ADP1111’s RLIM pin permits the switch current to be
limited with a single resistor. This current limiting action occurs
on a pulse by pulse basis. This feature allows the input voltage
to vary over a wide range without saturating the inductor or
exceeding the maximum switch rating. For example, a particular
design may require peak switch current of 800 mA with a 2.0 V
input. If VIN rises to 4 V, however, the switch current will
exceed 1.6 A. The ADP1111 limits switch current to 1.5 A and
thereby protects the switch, but the output ripple will increase.
Selecting the proper resistor will limit the switch current to
800 mA, even if VIN increases. The relationship between RLIM
and maximum switch current is shown in Figure 6.
The ILIM feature is also valuable for controlling inductor current
when the ADP1111 goes into continuous-conduction mode.
REV. 0
–11–
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