24-stage frequency divider and oscillator

The HEF4521B consists of a chain of 24 toggle flip-flops with an overriding asynchronous master reset input (MR), and an input circuit that allows three modes of operation. The single inverting stage (A2 to Y2) functions as: a crystal oscillator, an input buffer for an external oscillator or in combination with A1 as an RC oscillator. The crystal oscillator operates in Low-power mode when pins VSS1 and VDD1 are supplied via external resistors.

Each flip-flop divides the frequency of the previous flip-flop by two, consequently the HEF4521B counts up to 224 = 16777216. The counting advances on the HIGH-to-LOW transition of the clock (A2). The outputs from each of the last seven stages (218 to 224) are available for additional flexibility.

It operates over a recommended VDD power supply range of 3 V to 15 V referenced to VSS (usually ground). Unused inputs must be connected to VDD, VSS, or another input.

Features and benefits

  • Low power crystal oscillator operation
  • Fully static operation
  • 5 V, 10 V, and 15 V parametric ratings
  • Standardized symmetrical output characteristics
  • Specified from -40 °C to +85 °C
  • Complies with JEDEC standard JESD 13-B


Type numberProduct statusVCC (V)Output drive capability (mA)Logic switching levelstpd (ns)Power dissipation considerationsTamb (°C)Rth(j-a) (K/W)Ψth(j-top) (K/W)Rth(j-c) (K/W)Package name
HEF4521BTProduction4.5 - 15.5± 2.4CMOS220medium-40~85651.022.8SO16


Type numberPackagePackage informationReflow-/Wave solderingPackingStatusMarkingOrderable part number, (Ordering code (12NC))
Reel 13" Q1/T1 CECCActiveHEF4521BTHEF4521BT,653
( 9334 067 70653 )
Bulk Pack, CECCActiveHEF4521BTHEF4521BT,652
( 9334 067 70652 )

Quality, reliability & chemical content

Type numberOrderable part numberChemical contentRoHS / RHFLeadfree conversion dateEFRIFRMTBF (hour)MSLMSL leadfree
HEF4521BTHEF4521BT,653HEF4521BTweek 4, 200475.32.993.34E811
HEF4521BTHEF4521BT,652HEF4521BTweek 4, 200475.32.993.34E811
Quality and reliability disclaimer

Documentation (7)

File nameTitleTypeDate
HEF4521B24-stage frequency divider and oscillatorData sheet2017-03-16
AN11051Pin FMEA HEF4000 familyApplication note2019-01-09
Nexperia_Selection_guide_2020Nexperia Selection Guide 2020Selection guide2020-01-31
Nexperia_Selection_guide_2021Nexperia Selection Guide 2021Selection guide2021-01-08
SOT109-1plastic, small outline package; 16 leads; 1.27 mm pitch; 9.9 mm x 3.9 mm x 1.75 mm bodyPackage information2021-01-06
SO-SOJ-WAVEFootprint for wave solderingWave soldering2009-10-08
SO-SOJ-REFLOWFootprint for reflow solderingReflow soldering2009-10-08


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