MAX17004ETJ+ Maxim Integrated Products, MAX17004ETJ+ Datasheet - Page 25

• Manufacturer Part Number: MAX17004ETJ+
• Description: IC PS CTRLR FOR NOTEBOOKS 32TQFN
• Manufacturer: Maxim Integrated Products

Specifications of MAX17004ETJ+

• Applications: Controller, Notebook Computers
• Voltage - Input: 6 ~ 26 V
• Number Of Outputs: 4
• Voltage - Output: 3.3V, 5V, 2 ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 32-TQFN Exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

The MAX17003/MAX17004 include an auxiliary linear
regulator (OUTA) that can be configured for 12V, ideal for
PCMCIA power requirements, and for biasing the gates
of load switches in a portable device. OUTA can also be
configured for outputs from 1V to 23V. The auxiliary regu-
lator has an independent ON/OFF control, allowing it to
be shut down when not needed, reducing power con-
sumption when the system is in a low-power state.
A flyback-winding control loop regulates a secondary
winding output, improving cross-regulation when the pri-
mary output is lightly loaded or when there is a low input-
output differential voltage. If V
low-side switch is turned on for a time equal to 33% of
the switching period. This reverses the inductor (primary)
current, pulling current from the output filter capacitor
and causing the flyback transformer to operate in for-
ward mode. The low impedance presented by the trans-
former secondary in forward mode dumps current into
the secondary output, charging up the secondary
capacitor and bringing V
tion. The secondary feedback loop does not improve
secondary output accuracy in normal flyback mode,
where the main (primary) output is heavily loaded. In this
condition, secondary output accuracy is determined by
the secondary rectifier drop, transformer turns ratio, and
accuracy of the main output voltage.
Firmly establish the input voltage range and maximum
load current before choosing a switching frequency
and inductor operating point (ripple-current ratio). The
primary design trade-off lies in choosing a good switch-
ing frequency and inductor operating point, and the fol-
lowing four factors dictate the rest of the design:
•
•
Input Voltage Range. The maximum value
(V
AC-adapter voltage. The minimum value (V
must account for the lowest battery voltage after
drops due to connectors, fuses, and battery selector
switches. If there is a choice at all, lower input volt-
ages result in better efficiency.
Maximum Load Current. There are two values to
consider. The peak load current (I
determines the instantaneous component stresses
and filtering requirements and thus drives output
capacitor selection, inductor saturation rating, and
the design of the current-limit circuit. The continu-
ous load current (I
stresses and thus drives the selection of input
capacitors, MOSFETs, and other critical heat-con-
tributing components.
IN(MAX)
Supply Controllers for Notebook Computers
Auxiliary LDO Detailed Description
High-Efficiency, Quad-Output, Main Power-
) must accommodate the worst-case, high
SMPS Design Procedure
______________________________________________________________________________________
LOAD
INA
- V
) determines the thermal
OUTA
DRVA
back into regula-
< V
LOAD(MAX)
OUTA
IN(MIN)
, the
)
)
•
•
The switching frequency and inductor operating point
determine the inductor value as follows:
For example: I
f
Find a low-loss inductor having the lowest possible DC
resistance that fits in the allotted dimensions. Most induc-
tor manufacturers provide inductors in standard values,
such as 1.0µH, 1.5µH, 2.2µH, 3.3µH, etc. Also look for
non-standard values, which can provide a better compro-
mise in LIR across the input voltage range. If using a
swinging inductor (where the no-load inductance
decreases linearly with increasing current), evaluate the
LIR with properly scaled inductance values. For the
selected inductance value, the actual peak-to-peak
inductor ripple current (ΔI
OSC
Switching Frequency. This choice determines the
basic trade-off between size and efficiency. The opti-
mal frequency is largely a function of maximum input
voltage, due to MOSFET switching losses that are
proportional to frequency and V
quency is also a moving target, due to rapid improve-
ments in MOSFET technology that are making higher
frequencies more practical.
Inductor Operating Point. This choice provides
trade-offs between size vs. efficiency and transient
response vs. output ripple. Low inductor values pro-
vide better transient response and smaller physical
size, but also result in lower efficiency and higher out-
put ripple due to increased ripple currents. The mini-
mum practical inductor value is one that causes the
circuit to operate at the edge of critical conduction
(where the inductor current just touches zero with
every cycle at maximum load). Inductor values lower
than this grant no further size-reduction benefit. The
optimum operating point is usually found between
20% and 50% ripple current. When pulse skipping
(SKIP low and light loads), the inductor value also
determines the load-current value at which
PFM/PWM switchover occurs.
= 300kHz, 30% ripple current or LIR = 0.3:
L
=
ΔI
12
INDUCTOR
L
V x
LOAD(MAX)
=
5
V f
V x
300
IN OSC LOAD MAX
V
OUT IN
(
kHz x A x
12
=
V
INDUCTOR
(
I
V
V
= 5A, V
−
OUT IN
5
5
V
−
V f
)
(
(
IN OSC
V
V
Inductor Selection
OUT
0 3
IN
.
) is defined by:
IN
−
)
LIR
= 12V, V
=
2
)
V
L
. The optimum fre-
OUT
6 50
.
)
μ
H
OUT
= 5V,
25