Synergy Tier-1 distributor Jarwey｜SY2162QF receive blanking: clamp vs 40kΩ bleed
Jarwey is a Synergy (Xinlijie) Tier-1 distributor for medical ultrasound ICs, and can help with shortlisting, datasheets, samples, and lead time.
On the 16-channel HV switch SY2162QF, a 40kΩ probe-side shunt is easy to treat as the discharge path. Multiply that resistor by probe capacitance and the receive blank looks tens of microseconds long. After the main switch opens and the latch has updated, the fast dump is the clamp switch to ground (on-resistance typically about 35Ω). The 40kΩ shunt in parallel barely moves that time constant. Adding channels does not shorten this blank; that is a different selection problem.
The datasheet PDF is on the SY2162QF product page (SY2162 Rev.0.1). Figures below are from that revision. Production builds follow the latest PDF on the product page and your board measurement.
Which path actually discharges the probe
| Path | When it is the path | Resistance | Worked example at 220pF | What it sets | What it does not set |
|---|---|---|---|---|---|
| Clamp RONCL, probe side to GND | Main switch off, LEB low, CLR low, latch bit 0 (logic table: Main OFF, Clamp ON) | 35Ω typical no maximum listed | τ about 7.7ns 5τ about 40ns | Fast removal of probe-side charge after transmit | Switch turn-off time tOFF (2μs typical, 5μs max) |
| Bleed shunt RBLD, probe side | Always listed as a probe-side shunt. It dominates only while the clamp is not on | 30 / 40 / 50kΩ min / typ / max | At 40kΩ: τ about 8.8μs 5τ about 44μs | Slow tail and DC bleed on a capacitive load | Receive blank once the clamp is already on |
| Main switch RONS | Channel on (clamp off). SWxP faces the probe, SWxA faces the AFE | 8Ω typical, 10Ω max small-signal | Not an off-state discharge | Insertion loss on the signal path | Residual voltage after the switch opens |
220pF is the small-signal capacitive load used in the datasheet (CL=220pF), not a probe rating. Substitute the capacitance you measure. With the clamp on, 35Ω in parallel with 40kΩ still behaves like about 35Ω.
Analog range is 0V to ±100V from a single +5V rail; no separate HV supplies. Package is 48-LQFP, 7.0×7.0mm. Off isolation is about −57dB at 5MHz into 50Ω, crosstalk about −60dB. Those numbers do not tell you which discharge path you are on.
Supply-rail choice versus SY2160 is already covered in the 16-channel selection note. Logic level and shift-clock split for 32-channel SPST is the SY2325 / SY2326 note. This page only answers whether blanking should follow the clamp or the 40kΩ shunt.
Checklist
- Name the fault first. Near-field floor or a receive window held off by leftover probe voltage. A channel-count shortage belongs in the 32/64-channel notes.
- Pin the nodes. SWxP is the probe side, SWxA is the AFE side. Bleed and clamp act on the probe side.
- Read the logic table. With LEB low, CLR low, and that bit at 0, the main switch is off and the clamp is on. While LEB is high the latch holds; the shift clock alone does not move the switches.
- Do not infer CLR. When CLR is high the datasheet only states that every main switch is off. It does not state that the clamp is on. Measure residual voltage with CLR low, after the latch has taken the new word.
- Two time constants. Use measured probe capacitance. The 220pF column is a worked example. After the clamp is on, the blank still has to clear tOFF (2μs typical, 5μs max). A nanosecond RC does not erase turn-off time.
- Charge injection is a separate line. Typical injection is 10pC per switch. The voltage step is Q/C on your capacitance. The datasheet also lists spikes into 50Ω (about 40mV typical at turn-on, 60mV typical at turn-off). Do not fold that into the bleed time constant.
- Rates. 50MHz is the shift-clock ceiling. Analog switching frequency fSW tops out at 50kHz at 50% duty. Do not schedule the pulse-repetition rate from the shift clock. The 2A typical peak is a 100ns pulse at 0.1% duty through the main switch, not through the bleed resistor.
Datasheet, samples, lead time
- SY2162QF 16-channel HV analog switch (datasheet PDF)
Send probe capacitance, the blank you can allow, and the HV switch you use today. Jarwey can help with the cross-check, datasheet, samples, and lead time: kerry.w@jarwey.cn · contact.
Jarwey · Synergy Tier-1 distributor · kerry.w@jarwey.cn · contact.
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