LTC2238/LTC2237/LTC2236 10-Bit, 65/40/25Msps Low Noise 3V ADCs DESCRIPTIO U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ Sample Rate: 65Msps/40Msps/25Msps Single 3V Supply (2.7V to 3.4V) Low Power: 205mW/120mW/75mW 61.
LTC2238/LTC2237/LTC2236 U W U PACKAGE/ORDER I FOR ATIO U OVDD = VDD (Notes 1, 2) D7 D8 D9 OF MODE SENSE VDD VCM TOP VIEW Supply Voltage (VDD) ................................................. 4V Digital Output Ground Voltage (OGND) ....... –0.3V to 1V Analog Input Voltage (Note 3) ..... –0.3V to (VDD + 0.3V) Digital Input Voltage .................... –0.3V to (VDD + 0.3V) Digital Output Voltage ................ –0.3V to (OVDD + 0.3V) Power Dissipation ...........................................
LTC2238/LTC2237/LTC2236 U U A ALOG I PUT The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. (Note 4) SYMBOL PARAMETER CONDITIONS +– –) MIN TYP MAX UNITS ±0.5V to ±1V VIN Analog Input Range (AIN 2.7V < VDD < 3.4V (Note 7) ● VIN,CM Analog Input Common Mode (AIN+ + AIN–)/2 Differential Input (Note 7) Single Ended Input (Note 7) ● ● 1 0.
LTC2238/LTC2237/LTC2236 U U U I TER AL REFERE CE CHARACTERISTICS (Note 4) PARAMETER CONDITIONS MIN TYP MAX UNITS VCM Output Voltage IOUT = 0 1.475 1.500 1.525 V ±25 VCM Output Tempco ppm/°C VCM Line Regulation 2.7V < VDD < 3.4V 3 mV/V VCM Output Resistance –1mA < IOUT < 1mA 4 Ω U U DIGITAL I PUTS A D DIGITAL OUTPUTS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C.
LTC2238/LTC2237/LTC2236 U W POWER REQUIRE E TS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. (Note 8) MIN LTC2238 TYP MAX MIN LTC2237 TYP MAX MIN LTC2236 TYP MAX SYMBOL PARAMETER CONDITIONS UNITS VDD Analog Supply Voltage (Note 9) ● 2.7 3 3.4 2.7 3 3.4 2.7 3 3.4 V OVDD Output Supply Voltage (Note 9) ● 0.5 3 3.6 0.5 3 3.6 0.5 3 3.6 V IVDD Supply Current ● 68.
LTC2238/LTC2237/LTC2236 U W TYPICAL PERFOR A CE CHARACTERISTICS LTC2238: Typical INL, 2V Range, 65Msps LTC2238: 8192 Point FFT, fIN = 5MHz, –1dB, 2V Range, 65Msps LTC2238: Typical DNL, 2V Range, 65Msps 0 1.00 1.00 0.75 0.50 0.50 0.25 0 –0.25 –20 –30 AMPLITUDE (dB) 0.75 DNL ERROR (LSB) INL ERROR (LSB) –10 0.25 0 –0.25 –0.50 –0.50 –0.75 –0.75 –1.00 –1.
LTC2238/LTC2237/LTC2236 U W TYPICAL PERFOR A CE CHARACTERISTICS LTC2238: SNR and SFDR vs Sample Rate, 2V Range, fIN = 5MHz, –1dB LTC2238: SFDR vs Input Frequency, –1dB, 2V Range, 65Msps 100 LTC2238: SNR vs Input Level, fIN = 30MHz, 2V Range, 65Msps 100 80 70 SFDR 95 SFDR (dBFS) 90 85 80 75 80 70 SNR dBFS 60 SNR (dBc AND dBFS) SNR AND SFDR (dBFS) 90 50 dBc 40 30 20 60 70 10 65 50 100 50 200 150 INPUT FREQUENCY (MHz) 0 0 –60 0 10 20 30 40 50 60 70 80 90 100 110 SAMPLE RATE (Msps)
LTC2238/LTC2237/LTC2236 U W TYPICAL PERFOR A CE CHARACTERISTICS LTC2237: 8192 Point FFT, fIN = 70MHz, –1dB, 2V Range, 40Msps LTC2237: 8192 Point FFT, fIN = 30MHz, –1dB, 2V Range, 40Msps 0 –10 0 –10 –20 –20 –30 –40 –30 –40 –50 –60 –70 –80 AMPLITUDE (dB) –20 –30 –40 AMPLITUDE (dB) AMPLITUDE (dB) 0 –10 –50 –60 –70 –80 –60 –70 –80 –90 –90 –100 –100 –100 –110 –110 –110 –120 –120 –120 0 5 10 15 20 0 5 10 20 15 0 10 5 FREQUENCY (MHz) 223876 G20 LTC2237: 8192 Point 2-Tone FF
LTC2238/LTC2237/LTC2236 U W TYPICAL PERFOR A CE CHARACTERISTICS LTC2237: SFDR vs Input Level, fIN = 5MHz, 2V Range, 40Msps LTC2237: IOVDD vs Sample Rate, 5MHz Sine Wave Input, –1dB, OVDD = 1.
LTC2238/LTC2237/LTC2236 U W TYPICAL PERFOR A CE CHARACTERISTICS LTC2236: 8192 Point 2-Tone FFT, fIN = 10.9MHz and 13.8MHz, –1dB, 2V Range, 25Msps LTC2236: Grounded Input Histogram, 25Msps 0 70000 62.5 65520 –10 60000 –20 61.5 –30 –40 –50 –60 –70 SNR (dBFS) 50000 COUNT AMPLITUDE (dB) LTC2236: SNR vs Input Frequency, –1dB, 2V Range, 25Msps 40000 30000 59.5 –80 20000 –90 58.5 –100 10000 –110 –120 0 8 6 4 10 FREQUENCY (MHz) 2 0 0 0 12 511 512 CODE 57.
LTC2238/LTC2237/LTC2236 U U U PI FU CTIO S AIN+ (Pin 1): Positive Differential Analog Input. NC (Pins 12, 13, 14, 15): Do Not Connect These Pins. AIN- (Pin 2): Negative Differential Analog Input. D0-D9 (Pins 16, 17, 18, 19, 22, 23, 24, 25, 26, 27): Digital Outputs. D9 is the MSB. REFH (Pins 3, 4): ADC High Reference. Short together and bypass to pins 5, 6 with a 0.1µF ceramic chip capacitor as close to the pin as possible. Also bypass to pins 5, 6 with an additional 2.
LTC2238/LTC2237/LTC2236 W FUNCTIONAL BLOCK DIAGRA U U AIN+ AIN– VCM INPUT S/H FIRST PIPELINED ADC STAGE SECOND PIPELINED ADC STAGE THIRD PIPELINED ADC STAGE FOURTH PIPELINED ADC STAGE FIFTH PIPELINED ADC STAGE 1.5V REFERENCE SIXTH PIPELINED ADC STAGE SHIFT REGISTER AND CORRECTION 2.2µF RANGE SELECT REFH SENSE REFL INTERNAL CLOCK SIGNALS OVDD REF BUF OF D9 CLOCK/DUTY CYCLE CONTROL DIFF REF AMP CONTROL LOGIC OUTPUT DRIVERS • • • D0 REFH 0.
LTC2238/LTC2237/LTC2236 WU W TI I G DIAGRA tAP ANALOG INPUT N+4 N+2 N N+3 tH N+5 N+1 tL CLK tD D0-D9, OF N–5 N–4 N–3 N–2 N–1 N 223876 TD01 223876fa 13
LTC2238/LTC2237/LTC2236 U W U U APPLICATIO S I FOR ATIO DYNAMIC PERFORMANCE The signal-to-noise plus distortion ratio [S/(N + D)] is the ratio between the RMS amplitude of the fundamental input frequency and the RMS amplitude of all other frequency components at the ADC output. The output is band limited to frequencies above DC to below half the sampling frequency.
LTC2238/LTC2237/LTC2236 U W U U APPLICATIO S I FOR ATIO CONVERTER OPERATION SAMPLE/HOLD OPERATION AND INPUT DRIVE As shown in Figure 1, the LTC2238/LTC2237/LTC2236 is a CMOS pipelined multistep converter. The converter has six pipelined ADC stages; a sampled analog input will result in a digitized value five cycles later (see the Timing Diagram section). For optimal AC performance the analog inputs should be driven differentially.
LTC2238/LTC2237/LTC2236 U W U U APPLICATIO S I FOR ATIO Single-Ended Input For cost sensitive applications, the analog inputs can be driven single-ended. With a single-ended input the harmonic distortion and INL will degrade, but the SNR and DNL will remain unchanged. For a single-ended input, AIN+ should be driven with the input signal and AIN– should be connected to 1.5V or VCM. Common Mode Bias For optimal performance the analog inputs should be driven differentially. Each input should swing ±0.
LTC2238/LTC2237/LTC2236 U W U U APPLICATIO S I FOR ATIO VCM HIGH SPEED DIFFERENTIAL 25Ω AMPLIFIER ANALOG INPUT + – 2.2µF 2.2µF AIN+ + CM VCM 0.1µF LTC2238 LTC2237 LTC2236 25Ω – 25Ω 0.1µF T1 12pF 0.1µF AIN– AIN+ 12Ω ANALOG INPUT LTC2238 LTC2237 LTC2236 8pF 25Ω AIN– 12Ω T1 = MA/COM, ETC 1-1-13 RESISTORS, CAPACITORS ARE 0402 PACKAGE SIZE 223876 F04 223876 F06 Figure 4. Differential Drive with an Amplifier Figure 5 shows a single-ended input circuit.
LTC2238/LTC2237/LTC2236 U W U U APPLICATIO S I FOR ATIO Reference Operation Figure 9 shows the LTC2238/LTC2237/LTC2236 reference circuitry consisting of a 1.5V bandgap reference, a difference amplifier and switching and control circuit. The internal voltage reference can be configured for two pin selectable input ranges of 2V (±1V differential) or 1V (±0.5V differential). Tying the SENSE pin to VDD selects the 2V range; tying the SENSE pin to VCM selects the 1V range. The 1.
LTC2238/LTC2237/LTC2236 U W U U APPLICATIO S I FOR ATIO Input Range The input range can be set based on the application. The 2V input range will provide the best signal-to-noise performance while maintaining excellent SFDR. The 1V input range will have better SFDR performance, but the SNR will degrade by 0.6dB. See the Typical Performance Characteristics section. Driving the Clock Input The CLK input can be driven directly with a CMOS or TTL level signal.
LTC2238/LTC2237/LTC2236 U W U U APPLICATIO S I FOR ATIO Maximum and Minimum Conversion Rates DIGITAL OUTPUTS The maximum conversion rate for the LTC2238/LTC2237/ LTC2236 is 65Msps (LTC2238), 40Msps (LTC2237), and 25Msps (LTC2236). For the ADC to operate properly, the CLK signal should have a 50% (±5%) duty cycle. Each half cycle must have at least 7.3ns (LTC2238), 11.8ns (LTC2237), and 18.9ns (LTC2236) for the ADC internal circuitry to have enough settling time for proper operation.
LTC2238/LTC2237/LTC2236 U W U U APPLICATIO S I FOR ATIO Data Format Sleep and Nap Modes Using the MODE pin, the LTC2238/LTC2237/LTC2236 parallel digital output can be selected for offset binary or 2’s complement format. Connecting MODE to GND or 1/3VDD selects offset binary output format. Connecting MODE to 2/3VDD or VDD selects 2’s complement output format. An external resistor divider can be used to set the 1/3VDD or 2/3VDD logic values. Table 2 shows the logic states for the MODE pin.
LTC2238/LTC2237/LTC2236 U W U U APPLICATIO S I FOR ATIO Heat Transfer Most of the heat generated by the LTC2238/LTC2237/ LTC2236 is transferred from the die through the bottomside exposed pad and package leads onto the printed circuit board. For good electrical and thermal performance, the exposed pad should be soldered to a large grounded pad on the PC board. It is critical that all ground pins are connected to a ground plane of sufficient area.
J3 CLOCK INPUT R8 49.9Ω C12 0.1µF VDD E1 EXT REF VCM VDD R9 1k R7 1k L1 BEAD NC7SVU04 VCM VDD 4 2 EXT REF 5 6 3 1 JP3 SENSE 4 • C19 0.1µF R10 33Ω VDD GND VDD R16 1k R15 1k 7 5 3 1 GND 1/3VDD 2/3VDD VDD 8 6 4 GND C15 2.2µF VDD 2 C8 0.1µF 29 30 31 32 11 10 9 8 7 6 5 4 3 2 1 C20 0.1µF C2 12pF C11 0.1µF VDD JP4 MODE JP2 OE C7 2.2µF R6 24.9Ω R4 24.9Ω C4 0.1µF R14 1k VDD R2 24.9Ω R3 24.9Ω C14 0.
LTC2238/LTC2237/LTC2236 U W U U APPLICATIO S I FOR ATIO Silkscreen Top Topside 223876fa 24
LTC2238/LTC2237/LTC2236 U W U U APPLICATIO S I FOR ATIO Inner Layer 2 GND Inner Layer 3 Power 223876fa 25
LTC2238/LTC2237/LTC2236 U W U U APPLICATIO S I FOR ATIO Bottomside Silkscreen Bottom 223876fa 26
LTC2238/LTC2237/LTC2236 U PACKAGE DESCRIPTIO UH Package 32-Lead Plastic QFN (5mm × 5mm) (Reference LTC DWG # 05-08-1693) 0.70 ±0.05 5.50 ±0.05 4.10 ±0.05 3.45 ±0.05 (4 SIDES) PACKAGE OUTLINE 0.25 ± 0.05 0.50 BSC RECOMMENDED SOLDER PAD LAYOUT 5.00 ± 0.10 (4 SIDES) BOTTOM VIEW—EXPOSED PAD 0.23 TYP (4 SIDES) R = 0.115 TYP 0.75 ± 0.05 0.00 – 0.05 31 32 0.40 ± 0.10 PIN 1 TOP MARK (NOTE 6) 1 2 3.45 ± 0.10 (4-SIDES) (UH) QFN 0603 0.200 REF NOTE: 1.
LTC2238/LTC2237/LTC2236 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LTC1748 14-Bit, 80Msps, 5V ADC 76.3dB SNR, 90dB SFDR, 48-Pin TSSOP Package LTC1750 14-Bit, 80Msps, 5V Wideband ADC Up to 500MHz IF Undersampling, 90dB SFDR LT1993-2 High Speed Differential Op Amp 800MHz BW, 70dBc Distortion at 70MHz, 6dB Gain LT1994 Low Noise, Low Distortion Fully Differential Input/Output Amplifier/Driver Low Distortion: –94dBc at 1MHz LTC2202 16-Bit, 10Msps, 3.3V ADC, Lowest Noise 150mW, 81.