3.6A, 1.4MHz, Low-Voltage, Internal-Switch Step-Down Regulator with Dynamic Output Voltage Control

The MAX1536 constant-off-time, pulse-width-modulated (PWM) step-down DC-to-DC converter is ideal for use in +5.0V and +3.3V to low voltages for notebook and subnotebook computers. The MAX1536 features an internal PMOS power switch and internal synchronous rectification for high efficiency and reduced component count. No external Schottky diode is required across the internal synchronous rectifier switch. The internal 54mΩ PMOS power switch and 47mΩ NMOS synchronous-rectifier switch easily deliver continuous load currents up to 3.6A. The MAX1536 produces dynamically adjustable output voltages for chipsets and graphics processor cores using a logic-level control signal. The MAX1536 achieves efficiencies as high as 96%.

The MAX1536 uses a unique current-mode, constant-off-time, PWM control scheme. It has selectable Idle Mode™ to maintain high efficiency during light-load operation, or fixed-PWM mode for low output ripple. The programmable constant-off-time architecture allows a wide range of switching frequencies up to 1.4MHz, optimizing performance trade-offs between efficiency, output switching noise, component size, and cost. The MAX1536 features a digital soft-start to limit surge currents during startup, a 100% duty-cycle mode for low-dropout operation, and a low-power shutdown mode that disconnects the input from the output and reduces supply current below 1µA. The MAX1536 is available in a 28-pin thin QFN package with an exposed backside pad.

Applications

* Active Termination Buses * Chipset/Graphics Cores with Dual-Supply Voltages * DDR Memory Termination * Notebook Computers

* Dynamically Selectable Output Voltage from +0.7V to VIN

* Internal PMOS/NMOS Switches

* 54mΩ/47mΩ On-Resistance at VIN = +4.5V

* 63mΩ/53mΩ On-Resistance at VIN = +3.0V

* +3.0V to +5.5V Input Voltage Range

* 1.4MHz Maximum Switching Frequency

* 2V ±0.75% Reference Output

* Constant-Off-Time PWM Operation

* Selectable Idle Mode/PWM Operation at Light Loads

* 100% Duty Factor in Dropout

* Digital Soft-Start Inrush Current Limiting

* <1µA Typical Shutdown Supply Current

* <750µA Quiescent Supply Current

* Thermal Shutdown

* 1% VOUT Accuracy Over Line and Load

* External Reference Input

* Power-Good Window Comparator

* Selectable Power-Good Blanking Time During Output-Voltage Transition