ADP1111 Analog Devices, ADP1111 Datasheet - Page 14

• Manufacturer Part Number: ADP1111
• Description: Micropower, Step-Up/Step-Down SW Regulator; Adjustable and Fixed 3.3 V, 5 V, 12 V
• Manufacturer: Analog Devices

ADP1111
Voltage-Controlled Positive-to-Negative Converter
By including an op amp in the feedback path, a simple positive-
to-negative converter can be made to give an output that is a
linear multiple of a controlling voltage, Vc. The op amp, an
OP196, rail-to-rail input and output amplifier, sums the
currents from the output and controlling voltage and drives the
FB pin either high or low, thereby controlling the on-board
oscillator. The 0.22 Ω resistor limits the short-circuit current to
about 3 A and, along with the BAT54 Schottky diode, helps
limit the peak switch current over varying input voltages. The
external power switch features an active pull-up to speed up the
turn-off time of the switch. Although an IRF9530 was used in
the evaluation, almost any device that can handle at least 3 A of
peak current at a VDS of at least 50 V is suitable for use in this
application, provided that adequate attention is paid to power
dissipation. The circuit can deliver 2 W of output power with a
+6-volt input from a control voltage range of 0 V to 5 V.
+3 V to –22 V LCD Bias Generator
This circuit uses an adjustable-output version of the ADP1111
to generate a +22.5 V reference output that is level-shifted to
give an output of –22 V. If operation from a +5 volt supply is
desired, change R1 to 47 ohms. The circuit will deliver 7 mA
with a 3 volt supply and 40 mA with a 5 volt supply.
INPUT
+5V TO +12V
+3V
Figure 32. Voltage Controlled Positive-to-Negative
Converter
CELLS
2xAA
Figure 33. 3 V to –22 V LCD Bias Generator
AO
V
NC
2
6
IN
ADP1111
0.22Ω
R
SET
AO
I
NC
LIM
NC
1
LIM
L1 = CTX25-4
6
7
ADP1111
R
100Ω
I
LIM
GND
SET
LIM
1
NC
7
5
BAT54
GND
SW2
SW1
V
4
2
5
IN
FB
SW2
SW1
3
8
2kΩ
25μH
4
FB
L1
1N5818
1kΩ
1N5231
1N5818
3
8
4.7
μF
1N4148
6
1N4148
+
2N3904
7
D1
V
IN
4
+
IRF9530
732kΩ
42.2kΩ
2
3
IN5821
22μF
200kΩ
51Ω
D1
39kΩ
2W MAXIMUM OUTPUT
L1
CTX20-4
C
0.1μF
–V
L
V
OUTPUT
20μH
47μF
C
–22V OUTPUT
7mA @ 2V INPUT
OUT
35V
(0V TO +5V)
C
L
+
= –5.13 *V
OUTPUT
C
–14–
High Power, Low Quiescent Current Step-Down Converter
By making use of the fact that the feedback pin directly controls
the internal oscillator, this circuit achieves a shutdown-like state
by forcing the feedback pin above the 1.25 V comparator
threshold. The logic level at the 1N4148 diode anode needs to
be at least 2 V for reliable standby operation.
The external switch driver circuit features an active pull-up
device, a 2N3904 transistor, to ensure that the power MOSFET
turns off quickly. Almost any power MOSFET will do as the
switch as long as the device can withstand the 18 volt V
reasonably robust. The 0.22 Ω resistor limits the short-circuit
current to about 3 A and, along with the BAT54 Schottky
diode, helps to limit the peak switch current over varying input
voltages.
Figure 34. High Power, Low Quiescent Current Step-Down
Converter
NOTES
1. All inductors referenced are Coiltronics CTX-series except
2. If the source of power is more than an inch or so from the
OPERATE/STANDBY
2V ≤ V
where noted.
converter, the input to the converter should be bypassed with
approximately 10 μF of capacitance. This capacitor should
be a good quality tantalum or aluminum electrolytic.
INPUT
+8V TO +18V
IN
≤ 5
V
AO
NC
6
2
IN
ADP1111
1N4148
R
0.22
SET
NC
LIM
7
GND
I
LIM
1
5
BAT54
SW2
SW1
4
FB
3
8
2k
1N4148
LI = COILTRONICS CTX20-4
2N3904
IRF9540
S
G
40.2kΩ
D
121kΩ
51Ω
D1
IN5821
20μH
LI
+
GS
C
220μF
L
REV. 0
and is
500mA
+5V