MAX1533 Datasheet, PDF (23/38 Pages) Maxim Integrated Products – High-Efficiency, 5x Output, Main Power-Supply Controllers for Notebook Computers

High-Efficiency, 5x Output, Main Power-Supply
Controllers for Notebook Computers
t_ON(SKIP)
≥
I_IDLEL
V_IN - V_OUT
0
ON-TIME
I_LOAD(SKIP)
TIME
TO ERROR
AMPLIFIER
FB
REF
(2.0V)
12R
R
CSL
ADJUSTABLE
OUTPUT
FIXED OUTPUT
FB = GND
Figure 4. Pulse-Skipping/Discontinuous Crossover Point
Figure 5. Dual-Mode Feedback Decoder
Output Voltage
DC output accuracy specifications in the Electrical
Characteristics table refer to the error-comparator’s
threshold. When the inductor continuously conducts,
the MAX1533/MAX1537 regulate the peak of the output
ripple, so the actual DC output voltage is lower than the
slope-compensated trip level by 50% of the output rip-
ple voltage. For PWM operation (continuous conduc-
tion), the output voltage is accurately defined by the
following equation:
V_OUT(PWM)
⎛
= V_{NOM ⎝⎜}1 -
A_SLOPE V_NOM
V_IN
⎞
⎠⎟
-
⎛
⎝⎜
V_RIPPLE
2
⎞
⎠⎟
where V_NOM is the nominal output voltage, A_SLOPE
equals 1%, and V_RIPPLE is the output ripple voltage
(V_RIPPLE = ESR x ∆I_INDUCTOR as described in the
Output Capacitor Selection section).
In discontinuous conduction (I_OUT < I_LOAD(SKIP)), the
MAX1533/MAX1537 regulate the valley of the output
ripple, so the output voltage has a DC regulation level
higher than the error-comparator threshold. For PFM
operation (discontinuous conduction), the output volt-
age is approximately defined by the following equation:
V_OUT(PFM)
=
V_NOM
+
1
2
⎛
⎝⎜
f_SW
f_OSC
⎞
⎠⎟
I_IDLE
×
ESR
where V_NOM is the nominal output voltage, f_OSC is the
maximum switching frequency set by the internal oscil-
lator, f_SW is the actual switching frequency, and I_IDLE is
the idle-mode inductor current when pulse skipping.
Adjustable/Fixed Output Voltages
(Dual-Mode Feedback)
Connect FB3 and FB5 to GND to enable the fixed
SMPS output voltages (3.3V and 5V, respectively), set
by a preset, internal resistive voltage-divider connected
between CSL_ and analog ground. Connect a resistive
voltage-divider at FB_ between CSL_ and GND to
adjust the respective output voltage between 1V and
5.5V (Figure 5). Choose R2 (resistance from FB to
GND) to be about 10kΩ and solve for R1 (resistance
from OUT to FB) using the equation:
R1
=
R2
⎛ V_{OUT _}
⎝⎜ ^VFB _
⎞
− 1_⎠⎟
where V_{FB_} = 1V nominal.
______________________________________________________________________________________ 23