MAX1761EEE Maxim Integrated Products, MAX1761EEE Datasheet - Page 11

• Manufacturer Part Number: MAX1761EEE
• Description: DC/DC Switching Controllers
• Manufacturer: Maxim Integrated Products

Specifications of MAX1761EEE

• Number Of Outputs: 2
• Output Voltage: 2.5 V, 1 V to 5.5 V, 1.8 V
• Input Voltage: 4.5 V to 20 V
• Mounting Style: SMD/SMT
• Package / Case: QSOP-16
• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: - 40 C
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

The heart of the PWM core is the one-shot that sets the
high-side switch on-time for both controllers. This fast,
low-jitter, adjustable one-shot includes circuitry that
varies the on-time in response to battery and output
voltage. The high-side switch on-time is inversely pro-
portional to the battery voltage as measured by the V+
input, and proportional to the output voltage. This algo-
rithm results in a nearly constant switching frequency
despite the absence of a fixed-frequency clock genera-
tor. The benefits of a constant switching frequency are
Table 3. On-Time One-Shot
Figure 2. Functional Diagram
DEVICE
OUT1
OUT2
OUT1
C
OUT1
2.857
4.000
(µs)
OUT1
K
______________________________________________________________________________________
VL
L1
D1
C
C
L
IN1
On-Time One-Shot
ON1
(kHz)
Q1
Q2
MIN
318
227
DH1
CS1
-0.1V
OUT1
VL
V+
DL1
ON1
DRIVER
DRIVER
(kHz)
TYP
350
250
DL1
DL1
Buck Controller for Notebooks
VL
ZCC1
ILIM1
V
IN
(kHz)
MAX
428
278
Small, Dual, High-Efficiency
DH
ZERO
CROSSING
ILIM
DL
OUT
SHDN
LINEAR
REG
CONTROL
BLOCK
ON1
PWM
MAX1761
GND
twofold: first, the switching noise occurs at a known fre-
quency and is easily filtered; second, the inductor rip-
ple current remains relatively constant, resulting in
predictable output voltage ripple and a relatively sim-
ple design procedure. The difference in frequencies
between OUT1 and OUT2 prevents audio-frequency
“beating” and minimizes crosstalk between the two
SMPS. The on-times can be calculated by using the
equation below that references the K values listed in
Table 3.
The 0.1V offset term accounts for the expected drop
across the low-side MOSFET switch.
CONTROL
BLOCK
PWM
CROSSING
V
2V
REF
SHDN
ZERO
OUT
ILIM
DH
DL
V
IN
On - Time = K
ILIM2
ZCC2
VL
DH2
DL2
DRIVER
DRIVER
V
IN
VOS
-0.1V
OUT2
REF
CS2
ON2
DH2
DL2



V
OUT_
ON2
Q3
Q4
V
C
C
IN
IN2
+ 0.1V
REF
D2
L2
REF
V
IN



C
OUT2
OUT2
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