Simplified Block Diagram
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- Quick-PWM Slave Controller
- Precise, Active Current Balance (±1.25mV)
- Accurate, Adjustable Current-Limit Threshold
- Optimized for Low-Output Voltages (≤ 2V)
- 4V to 28V Battery Input Range
- Fixed 300kHz (MAX1887) or Selectable 200kHz/300kHz/550kHz (MAX1897) Switching Frequency
- Drive Large Synchronous-Rectifier MOSFETs
- 525µA (typ) ICC Supply Current
- 20µA Standby Supply Current
- < 1µA Shutdown (MAX1897) Supply Current
- Small 16-Pin QSOP (MAX1887), Compact 20-Pin 5mm x 5mm QFN (MAX1897), or 20-Pin 5mm x 5mm Thin QFN (MAX1897)
- CPU Core Supplies
- Notebook Computers
- Servers/Desktop Computers
- Single-Stage (BATT to VCORE) Converters
- Two-Stage (+5V to VCORE) Converters
The MAX1887/MAX1897 provide the same high efficiency, ultra-low duty factor capability, and excellent transient response as other Quick-PWM controllers. The MAX1887/MAX1897 differentially sense the inductor currents of both the master and the slave across current-sense resistors. These differential inputs and the adjustable current-limit threshold derived from an external reference allow the slave controller to accurately balance the inductor currents and provide precise current-limit protection. The MAX1887/MAX1897's dual-purpose current-limit input also allows the slave controller to automatically enter a low-power standby mode when the master controller shuts down.
The MAX1887 triggers on the rising edge of the master's low-side gate driver, which staggers the on-times of both master and slave, providing out-of-phase operation that can reduce the input ripple current and consequently the number of input capacitors. The MAX1897 features a selectable trigger polarity, allowing out-of-phase or simultaneous in-phase operation.