MAX1533ETJ+ Maxim Integrated Products, MAX1533ETJ+ Datasheet - Page 29

• Manufacturer Part Number: MAX1533ETJ+
• Description: IC POWER SUPPLY CONTROLER 32TQFN
• Manufacturer: Maxim Integrated Products

Specifications of MAX1533ETJ+

• Applications: Power Supply Controller
• Voltage - Input: 4.5 ~ 26 V
• Current - Supply: 15µA
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 32-TQFN Exposed Pad
• Product: Power Monitors
• Operating Temperature Range: - 40 C to + 85 C
• Mounting Style: SMD/SMT
• Accuracy: 1 %
• Sense Voltage (max): 5.5 V
• Supply Current (max): 35 uA
• Supply Voltage (max): 26 V
• Supply Voltage (min): 6 V
• Case: QFN
• Dc: 05+
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Supply: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

where L
transformer turns ratio, V
rectified secondary voltage, V
across the secondary rectifier, V
mum value of the main output voltage, and V
on-state voltage drop across the synchronous-rectifier
MOSFET. The transformer secondary return is often con-
nected to the main output voltage instead of ground to
reduce the necessary turns ratio. In this case, subtract
V
transformer turns-ratio equation above. The secondary
diode in coupled-inductor applications must withstand
flyback voltages greater than 60V. Common silicon recti-
fiers, such as the 1N4001, are also prohibited because
they are too slow. Fast silicon rectifiers such as the
MURS120 are the only choice. The flyback voltage
across the rectifier is related to the V
according to the transformer turns ratio:
where N is the transformer turns ratio (secondary wind-
ings/primary windings), and V
ondary DC output voltage. If the secondary winding is
returned to V
from V
reverse-breakdown voltage rating must also accommo-
date any ringing due to leakage inductance. The
diode’s current rating should be at least twice the DC
load current on the secondary output.
The inductor ripple current also impacts transient-
response performance, especially at low V
ferentials. Low inductor values allow the inductor
current to slew faster, replenishing charge removed
from the output filter capacitors by a sudden load step.
The total output voltage sag is the sum of the voltage
sag while the inductor is ramping up, and the voltage
sag before the next pulse can occur.
where D
Electrical Characteristics table), T is the switching period
OUT5
High-Efficiency, 5x Output, Main Power-Supply
V
from the secondary voltage (V
FLYBACK
SAG
PRIMARY
V
MAX
FLYBACK
N
=
=
OUT5
is the maximum duty factor (see the
2
V
C
OUT
in the equation above. The diode’s
is the primary inductance, N is the
∆
______________________________________________________________________________________
OUT
= V
I
instead of ground, subtract V
LOAD MAX
5
L
V
SEC
SEC
+
(
(
V
∆
(
IN
SEC
V
C
I
LOAD MAX
RECT
+ (V
OUT
Controllers for Notebook Computers
+
×
Transient Response
)
SEC
is the minimum required
FWD
V
D
IN
FWD
(
(
T
MAX
OUT5(MIN)
+
- V
is the maximum sec-
V
-
IN
is the forward drop
SENSE
SEC
OUT5
)
∆
)
- V
T
-
2
)
V
OUT
- V
OUT
) x N
IN
OUT5
is the mini-
RECT
- V
difference,
)
OUT
+
) in the
is the
OUT5
dif-
(1 / f
mode, or L x 0.2 x I
mode. The amount of overshoot during a full-load to no-
load transient due to stored inductor energy can be
calculated as:
The minimum current-limit threshold must be great
enough to support the maximum load current when the
current limit is at the minimum tolerance value. The
peak inductor current occurs at I
the ripple current; therefore:
where I
voltage divided by the current-sense resistance
(R
limit threshold is 70mV.
Connect ILIM_ to V
threshold. In adjustable mode, the current-limit thresh-
old is precisely 1/10th the voltage seen at ILIM_. For an
adjustable threshold, connect a resistive divider from
REF to analog ground (GND) with ILIM_ connected to
the center tap. The external 500mV to 2V adjustment
range corresponds to a 50mV to 200mV current-limit
threshold. When adjusting the current limit, use 1% tol-
erance resistors and a divider current of approximately
10µA to prevent significant inaccuracy in the current-
limit tolerance.
The current-sense method (Figure 9) and magnitude
determine the achievable current-limit accuracy and
power loss. Typically, higher current-sense limits pro-
vide tighter accuracy, but also dissipate more power.
Most applications employ a current-limit threshold
(V
be determined by:
For the best current-sense accuracy and overcurrent
protection, use a 1% tolerance current-sense resistor
between the inductor and output as shown in Figure
9a. This configuration constantly monitors the inductor
current, allowing accurate current-limit protection.
LIMIT
SENSE
OSC
) of 50mV to 100mV, so the sense resistor can
LIMIT
). For the default setting, the minimum current-
I
), and ∆T equals V
LIMIT
equals the minimum current-limit threshold
V
SOAR
>
R
I
LOAD MAX
SENSE
=
MAX
CC
(
Setting the Current Limit
(
= V
∆
for the default current-limit
2
I
/ (V
C
LOAD MAX
)
OUT
LIMIT
OUT
+
IN
⎛
⎜
⎝
(
/ V
∆
- V
/ I
V
I
INDUCTOR
LOAD(MAX)
IN
OUT
LIM
OUT
)
)
x T when in PWM
2
2
L
) when in skip
⎞
⎟
⎠
plus half
29