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Technical content

Features

  • High acoustic overload point (AOP, 131 dB SPL)
  • High signal-to-noise ratio (SNR, 66 dB)
  • Low variation in sensitivity (±1 dB)
  • Low current consumption — 650 A (High Performance Mode) — 160 A (Low Power Mode) —5 A (Standby Mode)
  • PDM digital audio output
  • Bottom-port LGA package
  • 1.8-V supply

Description

The CS7250B is a high-performance digital MEMS microphone, offering class-leading total harmonic distortion (THD) performance, excellent SNR, and low power consumption. The CS7250B supports two operational modes, selected according to the applied clock frequency. Low Power Mode is ideal for always-on voice activity detection; High Performance Mode is optimized for high fidelity recording. The CS7250B incorporates a high-performance ADC, which outputs a single-bit data stream using pulse density modulation (PDM) encoding. The CS7250B supports selectable left/right channel assignment for a two-channel digital microphone interface, enabling efficient connection of multiple microphones in stereo/array configurations. The CS7250B is available in a 3.50 x 2.65 x 0.98-mm bottom-port LGA package, with port diameter of 0.325 mm. It is ideal for portable applications such as smartphones, tablets, wearables and portable speech-recognition devices. Biasing PDM Digital Signal Processing High Performance Amp Ultralow Power ADC CMOS ASICMEMS Transducer CLK DATA VDD LRSEL GND Preliminary Product Information This document contains information for a new product. Cirrus Logic reserves the right to modify this product without notice. CS7250B

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1 Pin Descriptions

1.1 LGA Pinout

Figure 1-1. Top-Down (Through-Package) View

1.2 Pin Descriptions

A description of each pin on the CS7250B is provided in Table 1-1. Table 1-1. Pin Descriptions Name Pin # I/O Description DATA 1 O PDM data output LRSEL 2 I Channel select 0 = Data output following falling CLK edge 1 = Data output following rising CLK edge This pin must be tied to VDD or GND—ther e is no internal pull-up/-down provided. GND 3 Ground CLK 4 I Clock input VDD 5 Power supply

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2 Typical Connection Diagram

Figure 2-1. Typical Connection Diagram Stereo connection of two CS7250B digital microphones is shown in Fig. 2-1. It is recommended to connect a 0.1-F decoupling capacitor between the VDD and GND pins of the CS7250B. A ceramic 0.1-F capacitor with X7R dielectric or better is suitable. The capacitor should be placed as close to the CS7250B as possible. AP/CODEC CLK DATA AVDD 0.1µF CLK DATALRSEL GND 0.1µF CLK DATALRSEL GNDVDD VDD 1.8V 1.8V CS7250B CS7250B

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3 Characteristics and Specifications

Table 3-1. Parameter Definitions Parameter Definition Sensitivity A measure of the microphone output response to the acoustic pressure of a 1-kHz, 94 dB SPL (1 Pa RMS) sine wave. This is referenced to the output Full Scale Range (FSR) of the microphone. Full Scale Range (FSR) Sensitivity, electrical noise floor and powe r supply rejection are measured with reference to the output full scale range (FSR) of the microphone. FSR is defined as the amplitude of a 1-kHz sine-wave output whose positive peak value reaches 100% density of logic 1s and whose negative peak value reaches 0% density of logic 1s. This is the largest 1-kHz sine wave that fits in the digital output range without clipping. Note that, because the definition of FSR is based on a sine wave, it is possible to support a square wave test signal output whose level is +3 dBFS. Total harmonic distortion (THD) The ratio of the RMS sum of the har monic distortion products in the specified bandwidth (see note) relative to the RMS amplitude of the fundamental (i.e., test frequency) output. Signal-to-noise ratio (SNR) A measure of the difference in level be tween the output response of a 1-kHz, 94 dB SPL sine wave and the idle noise output. Dynamic Range (DR) The ratio of the 10% THD microphone output level (in response to a sine wave input) and the idle noise output. Note: Unless otherwise specified, all performance measurements are specified with a low-pass brick-wall filter and, where noted, an A-weighted filter. The low-pass filter removes out-of-band noise. Table 3-2. Recommended Operating Conditions Parameter Symbol Min Typ Max Units Supply voltage VDD 1.62 1.8 1.98 V Ground GND — 0 — V Clock frequency F CLK 0.3 — 3.2 MHz Operating temperature range T A –40 — +85 ºC Table 3-3. Absolute Maximum Ratings Absolute maximum ratings are stress ratings only. Permanent damage to the device may be caused by continuously operating at or beyond these limits. Device functional operating limits and guaranteed performance specifications are given under electrical characteristics at the test conditions specified. Parameter Symbol Min Max Units Supply voltage 1 1.All voltages are measured with respect to GND. VDD –0.3 2.4 V Input voltage 1 VIN –0.3 2.3 [2] 2.If VDD is above the minimum recommended operating level (see Table 3-2), the maximum input voltage is VDD + 0.3 V. V Input current 3 3.Input current is positive when flowing into the device. IIN –10 +10 mA Operating temperature range T A –40 +105 ºC Storage temperature prior to soldering T Stgp —3 0 º C Storage relative humidity prior to soldering RH Stgp —6 0 % Storage temperature after soldering T Stg –40 +105 ºC ESD-sensitive device. The CS7250B is manufactured on a CMOS process. It is therefore generically susceptible to damage from excessive static voltages. Proper ESD precautions must be taken during handling and storage of this device. This device is qualified to current JEDEC ESD standards

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Table 3-4. Acoustic and Electrical Characteristics Test conditions (unless specified otherwise): VDD = 1.8 V, GND = 0 V, CLK = 3.072 MHz, TA = +25ºC, 55 ±15% RH, 1-kHz, 94 dB SPL test signal, no load on DATA pin. Parameter 1 1.Performance measurements are specified with a low-pass brick-wall filter and, where noted, an A-weighted filter. The low-pass filter removes out-of-band noise. The Low Power Mode is measured with a cut-off frequency of 8 kHz; all other measurements are with a 20 kHz cut-off frequency. Min Typ Max Units General characteristics Directivity Omnidirectional — Polarity Positive sound pressure Increasing density of 1s — Sensitivity 2.Sensitivity is measured at production test 0.9 s after power up. –37 –36 –35 dBFS High Performance Mode (CLK = 3.072 MHz) Acoustic overload THD < 10% — 131 — dB SPL THD 94 dB SPL 125 dB SPL 0.2 SNR A-weighted — 66 — dB DR A-weighted — 103 — dB Acoustic noise floor A-weighted — 28 — dB SPL Electrical noise floor A-weighted — –102 — dBFS PSR (with respect to VDD) 100 mV p-p, swept sine wave,

20 Hz–20 kHz, A-weighted

— –90 — dBFS Low Power Mode (CLK = 768 kHz) Acoustic overload THD < 10% — 120 — dB SPL THD 117 dB SPL — 1 — % S N R 2 0H z – 8k H z , A - w e i g h t e d — 6 2 — d B DR 20 Hz–8 kHz, A-weighted — 88 — dB Acoustic noise floor 20 Hz–8 kHz, A-weighted — 32 — dB SPL Electrical noise floor 20 Hz–8 kHz, A-weighted — –98 — dBFS PSR (with respect to VDD) 100 mV p-p, swept sine wave,

20 Hz–8 kHz, A-weighted

— –90 — dBFS Frequency response Frequency response –3 dB low frequency +3 dB high frequency Hz kHz Frequency response flatness 200 Hz–8 kHz –1 — +1 dB Digital I/O 3.Note that digital input pins should not be left unconnected or floating. Input HIGH Level 0.65 VDD — — V Input LOW Level — — 0.35 VDD V Output HIGH Level I OH = 1 mA 0.9 VDD — — V Output LOW Level I OL = –1 mA — — 0.1 VDD V Input capacitance — 3 5 pF Input leakage –1 — 1 A Load capacitance (DATA) — — 200 pF Miscellaneous characteristics Current consumption 4 4.Measured without a load on the DATA pin. High Performance Mode, CLK = 3.072 MHz Low Power Mode, CLK = 768 kHz Standby Mode, CLK = 0 Hz 650 160 Startup time From power applied to output within 0.5 dB of sensitivity specification —1 5— m s Mode-transition time From Low Power Mode to High Performance Mode —1 0— m s CLK frequency range 5,6 5.High Performance and Low Power Modes are selected according to the CLK frequency. 6.Standby Mode is selected when the CLK input is stopped; this is a power-saving mode. Normal operation resumes automatically when the CLK input frequency is within the specified operational limits. Note that the VDD supply is still required in Standby Mode. High Performance Mode Low Power Mode Standby Mode 1.4 300 3.2 800 MHz kHz Hz

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Table 3-5. Audio Interface Timing The following timing information is valid across the full range of recommended operating conditions. Parameter 1 1.Digital microphone interface timing. Symbol Min Typ Max Units CLK cycle time t CY 313 — 3333 ns CLK duty cycle — 60:40 — 40:60 — CLK rise/fall time — — — 6 ns DATA enable time From rising CLK edge, LRSEL = 0 From falling CLK edge, LRSEL = 1 t R_EN tL_EN ns ns DATA valid time From rising CLK edge, LRSEL = 0 From falling CLK edge, LRSEL = 1 tR_DV tL_DV ns ns DATA disable time From falling CLK edge, LRSEL = 0 From rising CLK edge, LRSEL = 1 tR_DIS tL_DIS ns ns Notes:

  • The DATA output is high-impedance when not outputting data; this enables the outputs of two microphones to be connected together with the data from one microphone interleaved with the data from the other. (The microphones must be configured to transmit on oppos ite channels in this case.)
  • In a typical configuration, the left channel is transmitted following the rising CLK edge (LRSEL = 1). In this case, the left channel should be sampled by the receiving device on the falling CLK edge.
  • Similarly, the right channel is typically transmitted following the falling CLK edge (LRSEL = 0). In this case, the right cha nnel should be sampled by the receiving device on the rising CLK edge.
  • The CS7250B operating mode is selected according to the CLK frequency; see Table 3-4 for further details. tL_EN CLK (input) tL_DIS tR_EN tR_DIS tCY DATA is high-impedance (Hi-Z) when not outputting data DATA (LRSEL = 1) DATA (LRSEL = 0) tR_ DV tL_D V

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4 Typical Performance

4.1 Audio Frequency Response

Test conditions: VDD = 1.8 V, GND = 0 V, CLK = 3.072 MHz, no load on DATA pin. Figure 4-1. Sensitivity vs. Audio Frequency (20 Hz–20 kHz)

4.2 THD Performance

Test conditions: VDD = 1.8 V, GND = 0 V, CLK = 3.072 MHz, no load on DATA pin. Figure 4-2. THD (%) vs. Input Sound Pressure Level (dB SPL) -10.0 -9.0 -8.0 -7.0 -6.0 -5.0 -4.0 -3.0 -2.0 -1.0 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 10 100 1000 10000 100000 Sensitivity (dB) wrt. Sensitivity @ 1kHz Frequency (Hz) 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 THD (%) Input Sound Pressure Level (dB SPL)

5 Applications Information

Cirrus Logic provides a range of audio codecs incorporating a digital microphone input interface; these support direct connection to digital microphones such as the CS7250B. Further information on Cirrus Logic audio codecs is provided in the respective product data sheet, which is available from the Cirrus Logic website

5.1 Important Assembly Guidelines

  • Do not put a vacuum over the port hole of the micro phone. Placing a vacuum over the port hole can damage the device.
  • Do not board wash the microphone after a reflow process. Board washing and the associated cleaning agents can damage the device.
  • Do not expose to ultrasonic cleaning methods.
  • Do not use a vapor phase reflow proc ess. The vapor can damage the device.
  • Please refer to application note WAN0273 MEMS Mic Assembly and Handling Guidelines for further assembly and handling guidelines.

5.2 PCB Land Pattern and Paste Stencil

The recommended PCB land pattern and paste stencil pattern for the CS7250B microphone are shown in Fig. 5-1 and Fig. 5-2 respectively. See also application note WAN0284 General Design Considerations for MEMS Microphones for further details of PCB footprint design. Full definition of the package dimensions is provided in Section 6. The recommended PCB land pattern is shown in Fig. 5-1. Figure 5-1. PCB Land Pattern, Top View

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6 Package Dimension

The recommended PCB paste stencil pattern is shown in Fig. 5-2. Figure 5-2. PCB Paste Stencil, Top View

7 Ordering Information

Table 7-1. Ordering Information Product Description Package Halogen Free Pb Free Grade Temperature Range Container Order # CS7250B Digital MEMS Microphone with High Performance and Low Power Modes LGA Yes Yes Commercial –40 to +85°C Tape and Reel 1.Reel quantity = 5000 CS7250B–CAZR 2.650 (2.290) 3.500 (3.140) 0.980 ( 1.025) (2.240) (1.390) (R0.280) 1.040 1.325 4X (0.725) 4X (0.522) (0.290) 2X (1.675) 0.488 2X (0.822) 2X (1.252) 0.100 C

0.150 CAB

Unless otherwise specified, dimensions are in millimeters and tolerance is 0.100 Side View Bottom View A B C

8 References

  • WAN0273 MEMS Mic Assembly and Handling Guidelines
  • WAN0284 General Design Considerations for MEMS Microphones

9 Revision History

Table 9-1. Revision History Revision Changes PP1 MAY ‘17

  • Clarification of sensitivity specification added ( Table 3-4).
  • THD and frequency-response specifications updated ( Table 3-4).
  • Frequency response plot updated ( Section 4.2).
  • Order quantity updated ( Section 7). Contacting Cirrus Logic Support For all product questions and inquiries, contact a Cirrus Logic Sales Representative. To find the one nearest you, go to www.cirrus.com. IMPORTANT NOTICE “Preliminary” product information describes products that are in production, but for which full characterization data is not yet available. For the purposes of our terms and conditions of sale, “Preliminary” or “Advanced” data sheets are nonfinal data sheets that include, but are not limited to, data sheets marked as “Target”, “Advance”, “Product Preview”, “Preliminary Technical Data”, and/or “Preproduction”. Products provided with any such data sheet are therefore subject to relevant terms and conditions associated with “Preliminary” or “Advanced” designations. 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