MAX1999EEI Maxim Integrated Products, MAX1999EEI Datasheet - Page 28

• Manufacturer Part Number: MAX1999EEI
• Description: DC/DC Switching Controllers
• Manufacturer: Maxim Integrated Products

Specifications of MAX1999EEI

• Number Of Outputs: 1
• Output Voltage: 3.3 V, 2 V to 5.5 V
• Output Current: 0.95 A
• Input Voltage: 6 V to 24 V
• Mounting Style: SMD/SMT
• Package / Case: QSOP-28
• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: - 40 C
• Case: SSOP
• Dc: 07+/04+
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

High-Efficiency, Quad Output, Main Power-
Supply Controllers for Notebook Computers
an MBR0530 (500mA-rated) type for loads up to 1.5A, a
1N5819 type for loads up to 3A, or a 1N5822 type for
loads up to 10A. The rectifier’s rated reverse breakdown
voltage must be at least equal to the maximum input volt-
age, preferably with a 20% derating factor.
A signal diode, such as a 1N4148, works well in most
applications. Use a small (20mA) Schottky diode for
slightly improved efficiency and dropout characteris-
tics, if the input voltage can go below 6V. Do not use
large power diodes, such as 1N5817 or 1N4001, since
high-junction capacitance can force LDO5 to excessive
voltages.
The output voltage-adjust range for continuous-conduc-
tion operation is restricted by the nonadjustable 350ns
(max) minimum off-time one-shot. Use the slower 5V
SMPS for the higher of the two output voltages for best
dropout performance in adjustable feedback mode. The
duty-factor limit must be calculated using worst-case val-
ues for on- and off-times, when working with low input
voltages. Manufacturing tolerances and internal propaga-
tion delays introduce an error to the t
keep in mind that transient response performance of
buck regulators operated close to dropout is poor, and
bulk output capacitance must often be added (see the
V
The absolute point of dropout occurs when the inductor
current ramps down during the minimum off-time
(∆I
(∆I
slew the inductor current higher in response to
increased load, and must always be greater than 1. As
h approaches 1, the absolute minimum dropout point,
the inductor current is less able to increase during each
switching cycle and V
additional output capacitance is used.
A reasonable minimum value for h is 1.5, but this may
be adjusted up or down to allow tradeoffs between
V
voltage. For a given value of h, the minimum operating
voltage can be calculated as:
28
V
SAG
SAG
+
DOWN
UP
(
______________________________________________________________________________________
MIN
). The ratio h = ∆I
, output capacitance, and minimum operating
equation in the Output Capacitor Selection section).
)
) as much as it ramps up during the on-time
=
1
(
−
V
OUT
⎛
⎜
⎜
⎝
Applications Information
t
OFF MIN
_
+
(
V
K
UP
DROP
SAG
)
/∆I
×
DOWN
Dropout Performance
1
h
greatly increases unless
)
⎞
⎟
⎟
⎠
Boost Supply Diode
+
V
indicates the ability to
DROP
ON
2
K factor. Also,
−
V
DROP
1
where V
drops in the discharge and charge paths (see the On-
Time One-Shot section), t
and K is taken from Table 2. The absolute minimum
input voltage is calculated with h = 1.
Operating frequency must be reduced or h must be
increased and output capacitance added to obtain an
acceptable V
the required minimum input voltage. Calculate V
be sure of adequate transient response if operation
near dropout is anticipated.
MAX1977: With V
t
the minimum V+ is:
Calculating with h = 1 yields:
Therefore, V+ must be greater than 6.65V. A practical
input voltage with reasonable output capacitance
would be 7.5V.
Figure 12. Transformer-Coupled Secondary Output
OFF(MIN)
V
V
T1 = TRANSPOWER TECHNOLOGIES TTI-5870
+
+
(
MIN
(
MIN
MAX1777
MAX1977
MAX1999
DROP1
= 350ns, V
)
)
=
=
1
SAG
1
−
DH_
DL_
−
and V
⎛
⎜
⎝
(
OUT5
(
⎛
⎜
⎝
5
5
0 35
if calculated V+
0 35
DROP1
V
V
.
.
2 25
2 25
+
+
.
µ ×
.
DROP2
0 1
= 5V, fsw = 400kHz, K = 2.25µs,
µ ×
0 1
s
V+
.
s
.
µ
µ
= V
V
OFF(MIN)
s
V
s
)
1 5
)
1
DROP2
.
T1
10µH
1:2.2
⎞
⎟
⎠
Dropout Design Example
are the parasitic voltage
⎞
⎟
⎠
+
+
0 1
.
0 1
(MIN)
is from the EC table,
= 100mV, and h = 1.5,
V
MAX1658/
MAX1659
.
LDO
V
−
−
0 1
is greater than
.
0 1
.
V
V
=
12V
POSITIVE
SECONDARY
OUTPUT
5V
MAIN
OUTPUT
=
6 04
6 65
.
SAG
.
V
V
to