MAX1653EEE+ Maxim Integrated Products, MAX1653EEE+ Datasheet - Page 18

• Manufacturer Part Number: MAX1653EEE+
• Description: IC PWM STP-DN DC-DC CTRLR 16QSOP
• Manufacturer: Maxim Integrated Products
• Type: Step-Down (Buck)r

Specifications of MAX1653EEE+

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 2.5 ~ 5.5 V
• Current - Output: 10A
• Frequency - Switching: 150kHz, 300kHz
• Voltage - Input: 4.5 ~ 30 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 16-QSOP
• Power - Output: 667mW
• Output Voltage: 2.5 V to 5.5 V
• Output Current: 10 A
• Input Voltage: 4.5 V to 30 V
• Supply Current: 170 uA
• Switching Frequency: 300 KHz
• Mounting Style: SMD/SMT
• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

High-Efficiency, PWM, Step-Down
DC-DC Controllers in 16-Pin QSOP
With high input voltages, the required duty factor is
approximately (V
age drop across the synchronous rectifier. The
MAX1652’s minimum duty factor is determined by
delays through the feedback network, error comparator,
internal logic gate drivers, and the external MOSFETs,
which typically total 400ns. This delay is about 12% of
the switching period at 300kHz and 6% at 150kHz, limit-
ing the typical minimum duty factor to these values.
Even if the circuit can not attain the required duty factor
dictated by the input and output voltages, the output
voltage will remain in regulation. However, there may be
intermittent or continuous half-frequency operation. This
can cause a factor-of-two increase in output voltage rip-
ple and current ripple, which will increase noise and
reduce efficiency. Choose 150kHz operation for high-
input-voltage/low-output-voltage circuits.
A flyback winding control loop regulates a secondary
winding output (MAX1652/MAX1654 only), improving
cross-regulation when the primary is lightly loaded
or when there is a low input-output differential voltage.
If SECFB crosses its regulation threshold, a 1µs one-
shot is triggered that extends the low-side switch’s
Figure 7. Secondary-Output Feedback Dividers
18
______________________________________________________________________________________
Secondary Feedback-Regulation Loop
1-SHOT
TRIG
MAX1652
+V
TRIP
2.5V REF
= V
SECFB
OUT
REF
DH
DL
(
1 + –––
+ V
R2
R3
V+
)
Q2
)/ V
WHERE V
IN
, where V
REF
(NOMINAL) = 2.5V
R3
R2
(SECFB Pin)
Q2
is the volt-
POSITIVE
SECONDARY
OUTPUT
MAIN
OUTPUT
on-time beyond the point where the inductor current
crosses zero (in discontinuous mode). This causes the
inductor (primary) current to reverse, which in turn pulls
current out of the output filter capacitor and causes the
flyback transformer to operate in the forward mode. The
low impedance presented by the transformer secondary
in the forward mode dumps current into the secondary
output, charging up the secondary capacitor and bring-
ing SECFB back into regulation. The SECFB feedback
loop does not improve secondary output accuracy in
normal flyback mode, where the main (primary) output is
heavily loaded. In this mode, secondary output accura-
cy is determined (as usual) by the secondary rectifier
drop, turns ratio, and accuracy of the main output volt-
age. Hence, a linear post-regulator may still be needed
in order to meet tight output accuracy specifications.
The secondary output voltage-regulation point is deter-
mined by an external resistor-divider at SECFB. For neg-
ative output voltages, the SECFB comparator is
referenced to GND (MAX1654); for positive output volt-
ages, SECFB regulates at the 2.50V reference
(MAX1652). As a result, output resistor-divider connec-
tions and design equations for the two device types dif-
fer slightly (Figure 7). Ordinarily, the secondary
regulation point is set 5% to 10% below the voltage nor-
mally produced by the flyback effect. For example, if the
1-SHOT
TRIG
0.33 F
MAX1654
-V
TRIP
REF
= -V
SECFB
REF
DH
DL
(
–––
R2
R3
)
V+
R3 = 100k (RECOMMENDED)
R3
R2
NEGATIVE
SECONDARY
OUTPUT
MAIN
OUTPUT