General Description
The MAX1932 generates a low-noise, high-voltage output to bias avalanche photodiodes (APDs) in optical receivers. Very low output ripple and noise is achieved by constant-frequency, pulse-width modulated (PWM) boost topology combined with a unique architecture that maintains regulation with an optional RC or LC post filter inside its feedback loop. A precision reference and error amplifier maintain 0.5% output voltage accuracy.
The MAX1932 protects expensive APDs against adverse operating conditions while providing optimal bias. Traditional boost converters measure switch current for protection, whereas the MAX1932 integrates accurate high-side current limiting to protect APDs under avalanche conditions. A current-limit flag allows easy calibration of the APD operating point by indicating the precise point of avalanche breakdown. The MAX1932 control scheme prevents output overshoot and undershoot to provide safe APD operation without data loss.
The output voltage can be accurately set with either external resistors, an internal 8-bit DAC, an external DAC, or other voltage source. Output span and offset are independently settable with external resistors. This optimizes the utilization of DAC resolution for applications that may require limited output voltage range, such as 4.5V to 15V, 4.5V to 45V, 20V to 60V, or 40V to 90V.

Applications
Optical Receivers and Modules
Fiber Optic Network Equipment
Telecom Equipment
Laser Range Finders
PIN Diode Bias Supply

Benefits and Features
• Unique Architecture Delivers Excellent Accuracy for Improved System Performance
• 0.5% Accurate Output
• Low Ripple Output (< 1mV)
• Protection Features Guarantee Safe Operation
• Accurate High-Side Current Limit
• Avalanche Indicator Flag
• Output-Voltage Flexibility Facilitates Multiple Applications and Design Approaches
• 4.5V to 90V Output
• Set Output Voltage via 8-Bit SPI-Compatible Internal DAC, External DAC, or External Resistors
• Small Circuit Footprint Reduces Equipment Size
• 12-Pin, 4mm x 4mm Thin QFN Package
• Circuit Height < 2mm
• Commonly Available 2.7V to 5.5V Input Voltage Range