MIC4680BM Micrel Inc, MIC4680BM Datasheet - Page 9

• Manufacturer Part Number: MIC4680BM
• Description: IC REG BUCK 1A ADJ VOLT 8SOIC
• Manufacturer: Micrel Inc
• Series: SuperSwitcher™r
• Type: Step-Down (Buck)r

Specifications of MIC4680BM

• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: Adj to 1.25V
• Current - Output: 1.3A
• Frequency - Switching: 200kHz
• Voltage - Input: 4 ~ 34 V
• Operating Temperature: -40°C ~ 125°C
• Input Voltage: 34V
• Output Current: 1.3A
• Output Voltage: 5V
• No. Of Pins: 8
• Peak Reflow Compatible (260 C): No
• Supply Voltage Max: 34V
• Leaded Process Compatible: No
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant, Contains lead / RoHS non-compliant

Functional Description
The MIC4680 is a variable duty cycle switch-mode
regulator with an internal power switch. Refer to the
block diagrams.
Supply Voltage
The MIC4680 operates from a +4V to +34V unregulated
input. Highest efficiency operation is from a supply
voltage around +15V. See the efficiency curves.
Enable/Shutdown
The shutdown (SHDN) input is TTL compatible. Ground
the input if unused. A logic-low enables the regulator. A
logic-high shuts down the internal regulator which
reduces the current to typically 1.5µA when V
= 12V and 30µA when V
Behavior: Shutdown Hysteresis.”
Feedback
Fixed-voltage versions of the regulator have an internal
resistive divider from the feedback (FB) pin. Connect FB
directly to the output voltage.
Adjustable versions require an external resistive voltage
divider from the output voltage to ground, center tapped
to the FB pin. See Figure 6b for recommended resistor
values
Duty Cycle Control
A fixed-gain error amplifier compares the feedback
signal with a 1.23V bandgap voltage reference. The
resulting error amplifier output voltage is compared to a
200kHz sawtooth waveform to produce a voltage
controlled variable duty cycle output.
Micrel, Inc.
March 2008
SHDN
= 5V. See “Shutdown Input
SHDN
= V
IN
9
A higher feedback voltage increases the error amplifier
output
(comparator inverting input) causes the comparator to
detect only the peaks of the sawtooth, reducing the duty
cycle of the comparator output. A lower feedback voltage
increases the duty cycle. The MIC4680 uses a voltage-
mode control architecture.
Output Switching
When the internal switch is on, an increasing current
flows from the supply V
inductor L1, to output capacitor C
Energy is stored in the inductor as the current increases
with time.
When the internal switch is turned off, the collapse of the
magnetic field in L1 forces current to flow through fast
recovery diode D1, charging C
Output Capacitor
External output capacitor C
reduces
information.
Return Paths
During the on portion of the cycle, the output capacitor
and load currents return to the supply ground. During the
off portion of the cycle, current is being supplied to the
output capacitor and load by storage inductor L1, which
means that D1 is part of the high-current return path.
voltage.
ripple.
A
See
higher
“Bode
IN
OUT
, through external storage
OUT
provides stabilization and
error
.
Plots”
OUT
amplifier
M9999-032808
and the load.
for
MIC4680
additional
voltage