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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.

Orderable parts

Type number Orderable part number Ordering code (12NC) Package Buy from distributors
HEF4521BT HEF4521BT,653 933406770653 SOT109-1 Order product
HEF4521BT HEF4521BT,652 933406770652 SOT109-1 Order product

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 numberOrderable part number, (Ordering code (12NC))StatusMarkingPackagePackage informationReflow-/Wave solderingPacking
( 9334 067 70653 )
Reel 13" Q1/T1 CECC
( 9334 067 70652 )
ActiveHEF4521BTBulk Pack, CECC

Quality, reliability & chemical content

Type numberOrderable part numberChemical contentRoHS / RHFEFRIFRMTBF (hour)MSLMSL leadfree
Quality and reliability disclaimer

Documentation (4)

File nameTitleTypeDate
HEF4521B24-stage frequency divider and oscillatorData sheet2017-03-16
AN11051Pin FMEA HEF4000 familyApplication note2019-01-09
SO-SOJ-REFLOWFootprint for reflow solderingReflow soldering2009-10-08
SO-SOJ-WAVEFootprint for wave solderingWave soldering2009-10-08


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Ordering, pricing & availability

Type numberOrderable part numberOrdering code (12NC)PackingBuy online
HEF4521BTHEF4521BT,653933406770653Reel 13" Q1/T1 CECCOrder product
HEF4521BTHEF4521BT,652933406770652Bulk Pack, CECCOrder product


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