MAX1972EEE+ Maxim Integrated Products, MAX1972EEE+ Datasheet - Page 17

• Manufacturer Part Number: MAX1972EEE+
• Description: IC REG STP DWN 750MA 16-QSOP
• Manufacturer: Maxim Integrated Products
• Type: Step-Down (Buck)r

Specifications of MAX1972EEE+

• Internal Switch(s): Yes
• Synchronous Rectifier: Yes
• Number Of Outputs: 2
• Voltage - Output: 1.5V, 1.8V, 2.5V, 3.3V, Adj
• Current - Output: 750mA
• Frequency - Switching: 1.4MHz
• Voltage - Input: 2.6 ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 16-QSOP
• Power - Output: 667mW
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Table 1. Output Voltage Settings
For most designs, a reasonable inductor value (L
derived from the following equation:
Keep the inductor current ripple percentage LIR
between 20% and 40% of the maximum load current for
best compromise of cost, size, and performance. The
maximum inductor current is:
The input filter capacitor reduces peak currents drawn
from the power source and reduces noise and voltage
ripple on the input caused by the circuit’s switching.
The input capacitor must meet the ripple current
requirement (I
defined by the following equation:
A ceramic capacitor is recommended due to its low
equivalent series resistance (ESR), equivalent series
inductance (ESL), and lower cost. Choose a capacitor
that exhibits less than a 10°C temperature rise at the
maximum operating RMS current for optimum long-term
reliability.
Table 2. Suggested Inductors
Coilcraft
Sumida
Sumida
FBSEL1
MANUFACTURER
Open
GND
Dual, 180° Out-of-Phase, 1.4MHz, 750mA Step-
V
CC
I
RMS
L
INIT
=
V
=
RMS
1
I
IN
L MAX
OUTPUT 1
Ext Divider
V
(
IN
3.3V
1.8V
______________________________________________________________________________________
) imposed by the switching currents
I
OUT
I
OUT
×
)
Down Regulator with POR and RSI/PFO
=
V
LIR
1
2
OUT
2
⎡
⎢
⎣
2
1
CDRH3D16-4R7
×
+
×
×
V
LIR
CR43-4R7
(
V
OUT
DO1606
2
V
I
OU
PART
OUT MAX
IN
FBSEL2
⎤
⎥
⎦
Open
GND
T T
1
V
−
I
2
CC
(
OUT MAX
(
V
V
(
OUT
Input Capacitor
IN
V
IN
(
−
)
−
)
×
V
OUT
V
f
OUT
OSC
)
OUTPUT 2
Ext Divider
1
INDUCTANCE
)
2
2.5V
1.5V
+
)
INIT
(µH)
4.7
4.7
4.7
) is
The key selection parameters for the output capacitor
are its capacitance, ESR, ESL, and the voltage rating
requirements. These affect the overall stability, output
ripple voltage, and transient response of the DC-DC
converter.
The output ripple is due to variations in the charge
stored in the output capacitor, the voltage drop due to
the capacitor’s ESR, and the voltage drop due to the
capacitor’s ESL.
The output voltage ripple due to the output capaci-
tance, ESR, and ESL is:
V
whichever is greater.
I
These equations are suitable for initial capacitor selec-
tion, but final values should be set by testing a proto-
type or evaluation circuit. As a rule, a smaller ripple
current results in less output voltage ripple. Since the
inductor ripple current is a factor of the inductor value,
the output voltage ripple decreases with larger induc-
tance. Ceramic capacitors are recommended due to
their low ESR and ESL at the switching frequency of the
converter. For ceramic capacitors, the ripple voltage
due to ESL is negligible.
Load transient response depends on the selected out-
put capacitor. During a load transient, the output
instantly changes by ESR
P-P
RIPPLE (ESL)
108.7
(mΩ)
ESR
120
V
80
is the peak-to-peak inductor current:
RIPPLE
=
V
V
= (I
RIPPLE C
RIPPLE C
I
V
P P
SATURATION
CURRENT (A)
RIPPLE ESR
−
P-P
1.15
=
1.2
0.9
( )
( )
/T
V
ON
(
IN
f
=
+
SW
V
)
−
8
RIPPLE ESR

V
)
×

×
OUT
=
ESL or (I
∆I
C
L
I
P P
OUT
I
−
LOAD
P P
Output Capacitor
(
×
−
×
V
DIMENSIONS (mm)
×
OUT
V
ESR
)
IN
. Before the con-
3.8
P-P
+
f
SW
5.3
4.5
V
RIPPLE ESL
/T
✕
✕
✕
3.8
OFF
5.3
4
✕
✕
)
3.5
✕
(
0.8

2
ESL,
)
17