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Step-Down Controllers with Synchronous Rectifier for CPU Power

We Recommend Improved Performance Devices: MAX1652/MAX1653/MAX1654/MAX1655 for New Designs

Product Details

The MAX796/MAX797/MAX799 high-performance, step-down DC-DC converters with single or dual outputs provide main CPU power in battery-powered systems. These buck controllers achieve 96% efficiency by using synchronous rectification and Maxim's proprietary Idle Mode™ control scheme to extend battery life at full-load (up to 10A) and no-load outputs. Excellent dynamic response corrects output transients caused by the latest dynamic-clock CPUs within five 300kHz clock cycles. Unique bootstrap circuitry drives inexpensive N-channel MOSFETs, reducing system cost and eliminating the crowbar switching currents found in some PMOS/NMOS switch designs.

The MAX796/MAX799 are specially equipped with a secondary feedback input (SECFB) for transformer-based dual-output applications. This secondary feedback path improves cross-regulation of positive (MAX796) or negative (MAX799) auxiliary outputs.

The MAX797 has a logic-controlled and synchronizable fixed-frequency pulse-width-modulating (PWM) operating mode, which reduces noise and RF interference in sensitive mobile-communications and pen-entry applications. The SKIP-bar override input allows automatic switchover to idle-mode operation (for high-efficiency pulse skipping) at light loads, or forces fixed-frequency mode for lowest noise at all loads.

The MAX796/MAX797/MAX799 are all available in 16-pin DIP and narrow SO packages. See the table below to compare these three converters.

Key Features

  • 96% Efficiency
  • 4.5V to 30V Input Range
  • 2.5V to 6V Adjustable Output
  • Preset 3.3V and 5V Outputs (at up to 10A)
  • Multiple Regulated Outputs
  • +5V Linear-Regulator Output
  • Precision 2.505V Reference Output
  • Automatic Bootstrap Circuit
  • 150kHz/300kHz Fixed-Frequency PWM Operation
  • Programmable Soft-Start
  • 375µA Typ Quiescent Current (VIN = 12V, VOUT = 5V)
  • 1µA Typ Shutdown Current

Applications/Uses

  • Cell Phones
  • Notebook and Subnotebook Computers
  • PDAs and Mobile Communicators
Parametric specs for Step-Down Switching Regulators
VIN (V) (min) 4.5
VIN (V) (max) 30
VOUT1 (V) (min) 2.5
VOUT1 (V) (max) 6
IOUT1 (A) (max) 10
Switch Type External
Preset VOUT (V) 5
Output Adjust. Method Preset
Resistor
Synchronous Switching? Yes
# DC-DC Outputs 1
Switching Frequency (kHz) 340
Package/Pins SOIC (N)/16
Budgetary
Price (See Notes)
$5.85 @1k
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Simplified Block Diagram

MAX796, MAX797, MAX799: Typical Operating Circuits MAX796, MAX797, MAX799: Typical Operating Circuits Zoom icon

Technical Docs

Design & Development

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Description

The MAX797 evaluation kit (EV kit) is a preassembled and tested demonstration board that embodies the standard 3.3V application circuit. The board comes configured to accept battery voltages between 4.5V and 28V, but can be reconfigured for voltages between 4.5V and 30V by substituting MOSFETs with higher breakdown voltage ratings.

The standard board is guaranteed to deliver at least 3A of load current. To modify the load-current capability, change the sense-resistor (R1) value and re-size the external components according to Table 1 in the MAX796/MAX797/MAX799 data sheet.

The main output voltage comes preset to 3.35V (nominal). To select 5V operation, move jumper J3 to position 1-2. For operation in adjustable mode, install resistors R4 & R5 and remove the jumper. There is a small PC trace jumper that shunts J3 on the board. This default jumper must be cut apart for either adjustable-mode or fixed 5V operation. Don't operate the circuit if a jumper or resistor divider has not been installed, as this will damage the IC due to output overvoltage.

In addition to the standard components, the EV kit has some extra pull-up and pull-down resistors (R4-R8) to set default logic input levels. These resistors can usually be omitted in the final design.

View Details

Features

  • Battery Range: 4.5V to 28V
  • Load Capability: 3.3V at 3A
  • Adjustable 2.5V to 6V Output (optional resistor divider)
  • Precision 2.505V Reference Output
  • Oscillator SYNC Input
  • Low-Noise Mode Control Input

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Support & Training

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Parameters

Parametric specs for Step-Down Switching Regulators
VIN (V) (min) 4.5
VIN (V) (max) 30
VOUT1 (V) (min) 2.5
VOUT1 (V) (max) 6
IOUT1 (A) (max) 10
Switch Type External
Preset VOUT (V) 5
Output Adjust. Method Preset
Resistor
Synchronous Switching? Yes
# DC-DC Outputs 1
Switching Frequency (kHz) 340
Package/Pins SOIC (N)/16
Budgetary
Price (See Notes)
$5.85 @1k

Key Features

  • 96% Efficiency
  • 4.5V to 30V Input Range
  • 2.5V to 6V Adjustable Output
  • Preset 3.3V and 5V Outputs (at up to 10A)
  • Multiple Regulated Outputs
  • +5V Linear-Regulator Output
  • Precision 2.505V Reference Output
  • Automatic Bootstrap Circuit
  • 150kHz/300kHz Fixed-Frequency PWM Operation
  • Programmable Soft-Start
  • 375µA Typ Quiescent Current (VIN = 12V, VOUT = 5V)
  • 1µA Typ Shutdown Current

Applications/Uses

  • Cell Phones
  • Notebook and Subnotebook Computers
  • PDAs and Mobile Communicators

Description

The MAX796/MAX797/MAX799 high-performance, step-down DC-DC converters with single or dual outputs provide main CPU power in battery-powered systems. These buck controllers achieve 96% efficiency by using synchronous rectification and Maxim's proprietary Idle Mode™ control scheme to extend battery life at full-load (up to 10A) and no-load outputs. Excellent dynamic response corrects output transients caused by the latest dynamic-clock CPUs within five 300kHz clock cycles. Unique bootstrap circuitry drives inexpensive N-channel MOSFETs, reducing system cost and eliminating the crowbar switching currents found in some PMOS/NMOS switch designs.

The MAX796/MAX799 are specially equipped with a secondary feedback input (SECFB) for transformer-based dual-output applications. This secondary feedback path improves cross-regulation of positive (MAX796) or negative (MAX799) auxiliary outputs.

The MAX797 has a logic-controlled and synchronizable fixed-frequency pulse-width-modulating (PWM) operating mode, which reduces noise and RF interference in sensitive mobile-communications and pen-entry applications. The SKIP-bar override input allows automatic switchover to idle-mode operation (for high-efficiency pulse skipping) at light loads, or forces fixed-frequency mode for lowest noise at all loads.

The MAX796/MAX797/MAX799 are all available in 16-pin DIP and narrow SO packages. See the table below to compare these three converters.

Simplified Block Diagram

MAX796, MAX797, MAX799: Typical Operating Circuits MAX796, MAX797, MAX799: Typical Operating Circuits Zoom icon

Technical Docs

Support & Training

Search our knowledge base for answers to your technical questions.

Filtered Search

Our dedicated team of Applications Engineers are also available to answer your technical questions. Visit our support portal