ADP3050-3.3 Analog Devices, ADP3050-3.3 Datasheet - Page 15

• Manufacturer Part Number: ADP3050-3.3
• Description: 200 Khz, 1 a Step-down High-voltage Switching Regulator
• Manufacturer: Analog Devices

TYPICAL APPLICATIONS
5 V to 3.3 V Buck (Step-Down) Regulator
The circuit in Figure 5 shows the ADP3050 in a buck configu-
ration. It is used to generate 3.3 V regulated output from 5 V
input voltage with the following specifications:
INVERTING (BUCK-BOOST) REGULATOR
The circuit in Figure 6 shows the ADP3050 in a buck-boost
configuration, which produces a negative output voltage from a
positive input voltage. This topology looks quite similar to the
buck shown in Figure 5 above (except the IC and the output filter
are now referenced to the negative output instead of ground), but
1N5817
GND
D1
V
SD
IN
5V
V
V
I
I
V
OUT
RIPPLE
IN
OUT
OUT RIPPLE
= 4.5 V to 5.5 V
= 0.75 A
C3
0.22 F
= 3.3 V
OUTPUT
= 0.4 A
22 H
R2
+
L1
1N4148
C1
22 F
D2
= 50 mV
D2
L1
0.75 A = 0.3 A
R1
C2
C2
0.01 F
C1
1
2
3
4
ADP3050-3.3
GROUND
SWITCH
BOOST
BIAS
FB
U1
CC
D1
COMP
C3
ADP3050
GND
SD
IN
8
7
6
5
7.5k
INPUT
RC
R1
+ C5
C4
1nF
100 F
3.3V
V
OUT
its operation is quite different. For this topology, the feedback
pin is grounded and the GND pin is tied to the negative output,
allowing the feedback network of the IC to regulate the negative
output voltage.
The design procedure used for the standard buck converter cannot
be used for a buck-boost converter due to fundamental differences
in how the output voltage is generated. The switch currents in the
buck-boost are much higher than in the standard buck converter,
thus lowering the available load current. To calculate the maximum
output current for a given maximum switch current use the fol-
lowing equation:
where I
and V
can be estimated using the following equation:
For the circuit in Figure 6, the maximum ripple current (at the
maximum input voltage) is:
High ripple currents are present in both the input and output
capacitors, and their ripple current ratings must be large enough
to sustain the large switching currents present in this topology.
The capacitors should have a ripple current rating of at least:
The peak current seen by the diode, switch, and inductor can be
found by rearranging the load current equation:
GND
V
SD
47 H
1N5818
IN
L1
I
12V
RIPPLE
IN
D1
I
SW(MAX)
I
RIPPLE
is the minimum input voltage. The inductor ripple current
PEAK
I




OUT
I
SW
+
=
1N4148
C3
0.22 F
C1
22 F
(MAX)
(MAX)
47 10
I
=
=
RMS
is the switch current limit rating of the ADP3050
D2



V
×
12
V
NC
IN
(CIN, COUT)
IN
=
−
(MAX)
L
−
V
V
+
2
6
C2
0.01 F
IN
IN
×
1
2
3
4
V
×
OUT
V
f
200 10
+
SWITCH
BOOST
BIAS
FB
ADP3050-5
SW
×
IN
V
f
V
≈
SW
OUT
×
1
1
×
U1
×
IN
I
L
I
OUT
COMP
OUT
×
GND
×
×
3
SD
×
V
IN
(
V
V
×
×
IN

 +

OUT
IN
12
8
7
6
5
(MAX)
5.1k



+
V
+ −
V
−
V
1
2
R1
OUT
OUT
V
5
IN
×
ADP3050
OUT
+
5
I
C4
3.3nF
RIPPLE
V
=
OUT
)
100 F




0 375
.
C5



5V @ 0.5A
+
A
(17)
(15)
(16)
(18)
V
OUT