Allegro DCDC Convertors

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Allegro DC/DC Convertors

• Mike Sandyck
• Technical Marketing Manager
• May 2007

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Allegro DC/DC Convertors
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General Purpose DC/DC Convertors
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What are the products?

• 1.5A (A8499) and 4A (A8698) step-down regulators
• Wide input voltage range up to 50V
• Fixed off-time current-mode-controlled buck
  regulators. Off time is determined by an
  external resistor.
• Will operate in both continuous and discontinuous
  modes.
• Internal blanking circuit Filters out
  transients due to the reverse recovery of the
  external clamp diode. Typical blanking time is
  200 nS.
• A8499/98 differences include output current
  (1.5/3A), feedback voltage (1.2/0.8V), and Rdson
  (lower for A8498)

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Features and Benefits

• 8-50 V input range
• Very wide input voltage range
• Integrated DMOS switch
• Ö No external FET needed
• Adjustable fixed off-time
• Ö User adjustability
• Adjustable output1.2-24V (A8499) or 0.8-24V
  (A8498)
• Ö User adjustability

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Features and Benefits

• Flat efficiency curve across output current
• Ö Minimal change in efficiency across wide
  operating range
• 1.5 to 4.0 Amp output in standard SOIC-8 package
• Ö Output current capability in small package with
• integrated FET
• Low shutdown current
• Ö Maximized battery life and low power drain
• Internal Compensation
• Ö Minimizes number of external components
  required

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Block Diagram (A8498/99)
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Typical Application Circuit (A8499)
Bootstrap capacitor
Input Capacitor
Inductor
Output Capacitor
Voltage divider
Setup off time
Use Vout as internal bias voltage

• 12V down to 5.0V _at_1.8A

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Typical Application Circuit (A8697)
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Competitive Advantages
Allegro has smaller package and more cost
effective solution, and full 50V input as opposed
to 18V or 25V for others

• 8-50 V input range
• Integrated DMOS switch
• Low RDSon typ 180mOhm _at_ 25C / 3A
• Flat efficiency curve across output current
• 1.5 or 3.0A output in standard SOIC-8 package
• Low shutdown current
• Low cost

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