MAX17004ETJ+ Maxim Integrated Products, MAX17004ETJ+ Datasheet - Page 21

• 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

Table 4. FSEL Configuration Table
The FSEL input selects the PWM mode switching fre-
quency. Table 4 shows the switching frequency based
on FSEL connection. High-frequency (500kHz) operation
optimizes the application for the smallest component
size, trading off efficiency due to higher switching losses.
This may be acceptable in ultraportable devices where
the load currents are lower. Low-frequency (200kHz)
operation offers the best overall efficiency at the expense
of component size and board space.
The low-noise forced-PWM mode (SKIP = LDO5) dis-
ables the zero-crossing comparator, which controls the
low-side switch on-time. This forces the low-side gate-
drive waveform to be constantly the complement of the
high-side gate-drive waveform, so the inductor current
reverses at light loads while DH_ maintains a duty factor
of V
the switching frequency fairly constant. However, forced-
PWM operation comes at a cost: the no-load 5V supply
current remains between 20mA to 50mA, depending on
the external MOSFETs and switching frequency.
Forced-PWM mode is most useful for avoiding audio-
frequency noise and improving load-transient
response. Since forced-PWM operation disables the
zero-crossing comparator, the inductor current revers-
es under light loads.
The MAX17003/MAX17004 include a light-load operat-
ing mode control input (SKIP) used to enable or dis-
able the zero-crossing comparator for both switching
regulators. When the zero-crossing comparator is
enabled, the regulator forces DL_ low when the cur-
rent-sense inputs detect zero inductor current. This
keeps the inductor from discharging the output capaci-
tors and forces the regulator to skip pulses under light-
load conditions to avoid overcharging the output. When
the zero-crossing comparator is disabled, the regulator
is forced to maintain PWM operation under light-load
conditions (forced-PWM).
OUT
LDO5
FSEL
/V
GND
REF
Light-Load Operation Control ( SKIP )
IN
Supply Controllers for Notebook Computers
. The benefit of forced-PWM mode is to keep
High-Efficiency, Quad-Output, Main Power-
______________________________________________________________________________________
SWITCHING FREQUENCY (kHz)
Frequency Selection (FSEL)
Forced-PWM Mode
500
300
200
When pulse-skipping mode is enabled, the on-time of the
step-down controller terminates when the output voltage
exceeds the feedback threshold and when the current-
sense voltage exceeds the idle-mode current-sense
threshold. Under light-load conditions, the on-time dura-
tion depends solely on the idle mode current-sense
threshold, which is 20% (SKIP = GND) of the full-load
current-limit threshold set by ILIM, or the low-noise cur-
rent-sense threshold, which is 10% (SKIP = REF) of the
full-load current-limit threshold set by ILIM. This forces
the controller to source a minimum amount of power with
each cycle. To avoid overcharging the output, another
on-time cannot begin until the output voltage drops
below the feedback threshold. Since the zero-crossing
comparator prevents the switching regulator from sinking
current, the controller must skip pulses. Therefore, the
controller regulates the valley of the output ripple under
light-load conditions.
In skip mode, an inherent automatic switchover to PFM
takes place at light loads (Figure 4). This switchover is
affected by a comparator that truncates the low-side
switch on-time at the inductor current’s zero crossing.
The zero-crossing comparator senses the inductor cur-
rent across CSH_ to CSL_. Once (V
drops below the 3mV zero-crossing, current-sense
threshold, the comparator forces DL_ low (Figure 3).
This mechanism causes the threshold between pulse-
skipping PFM and nonskipping PWM operation to coin-
cide with the boundary between continuous and
Figure 4. Pulse-Skipping/Discontinuous Crossover Point
0
ON-TIME
Automatic Pulse-Skipping Crossover
Idle Mode Current-Sense Threshold
t
ON(SKIP)
=
V
V
IN
OUT
f
OSC
TIME
CSH
_ - V
I
I
PK
LOAD
= I
CSL
PK
/2
21
_)