MAX1637EEE Maxim Integrated Products, MAX1637EEE Datasheet - Page 11

• Manufacturer Part Number: MAX1637EEE
• Description: IC CTRLR MINI LV STPDWN 16-QSOP
• Manufacturer: Maxim Integrated Products
• Type: Step-Down (Buck)r

Specifications of MAX1637EEE

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 1.1 ~ 5.5 V
• Current - Output: 3A
• Frequency - Switching: Adj to 350kHz
• Voltage - Input: 3.15 ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 16-QSOP
• Power - Output: 667mW
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

When SKIP is low, idle-mode circuitry automatically
optimizes efficiency throughout the load-current range.
Idle mode dramatically improves light-load efficiency
by reducing the effective frequency, subsequently
reducing switching losses. It forces the peak inductor
current to ramp to 30% of the full current limit, deliver-
ing extra energy to the output and allowing subsequent
cycles to be skipped. Idle mode transitions seamlessly
to fixed-frequency PWM operation as load current
increases (Table 3).
When SKIP is high, the controller always operates in
fixed-frequency PWM mode for lowest noise. Each pulse
from the oscillator sets the main PWM latch that turns on
the high-side switch for a period determined by the duty
factor (approximately V
turns off, the synchronous rectifier latch is set; 60ns later,
the low-side switch turns on. The low-side switch stays on
until the beginning of the next clock cycle.
In PWM mode, the controller operates as a fixed-fre-
quency, current-mode controller in which the duty fac-
tor is set by the input/output voltage ratio. PWM mode
(SKIP = high) forces two changes on the PWM con-
troller. First, it disables the minimum-current compara-
tor, ensuring fixed-frequency operation. Second, it
changes the detection threshold for reverse-current
limit from 0mV to -100mV, allowing the inductor current
to reverse at light loads. This results in fixed-frequency
operation and continuous inductor-current flow. PWM
mode eliminates discontinuous-mode inductor ringing
and improves cross-regulation of transformer-coupled,
multiple-output supplies.
Figure 4. Main PWM Comparator Functional Diagram
CSH
CSL
REF
CC
I1
______________________________________________________________________________________
SLOPE COMPENSATION
OUT
FB
/ V
IN
). As the high-side switch
I2
Fixed-Frequency Mode
Precision Step-Down Controller
Idle Mode
R1
I3
V
CC
R2
Miniature, Low-Voltage,
The current-mode feedback system regulates the peak
inductor-current value as a function of the output volt-
age error signal. In continuous-conduction mode, the
average inductor current is nearly the same as the
peak current, so the circuit acts as a switch-mode
transconductance amplifier. This pushes the second
output LC filter pole, normally found in a duty-factor-
controlled (voltage-mode) PWM, to a higher frequency.
To preserve inner-loop stability and eliminate regenera-
tive inductor-current “staircasing,” a slope-compensa-
tion ramp is summed into the main PWM comparator to
make the apparent duty factor less than 50%.
The relative gains of the voltage-sense and current-
sense inputs are weighted by the values of the current
sources that bias four differential input stages in the
main PWM comparator (Figure 4). The voltage sense
into the PWM has been conditioned by an integrated
component of the feedback voltage, yielding excellent
DC output voltage accuracy. See the Output Voltage
Accuracy section for details.
Table 3. SKIP PWM Table
SKIP
High
High
Low
Low
I4
CURRENT
LOAD
Heavy
Heavy
Light
Light
UNCOMPENSATED
HIGH-SPEED
LEVEL TRANSLATOR
AND BUFFER
V
BIAS
MODE
PWM
PWM
PWM
Idle
Pulse-skipping, discontin-
uous inductor current
Constant frequency PWM,
continuous inductor current
Constant frequency PWM,
continuous inductor current
Constant frequency PWM,
continuous inductor current
OUTPUT DRIVER
DESCRIPTION
TO PWM
LOGIC
11