Ying Lin
No. It is a 3.3 V SDR SDRAM with a 16M × 16 organization and 256 Mbit capacity, equivalent to 32 MiB. It uses SDR command and timing requirements. DDR or LPDDR compatibility cannot be inferred from density or the broad DRAM category.
No. Its ordering row specifies the 143 MHz -7 grade. For 143 MHz SDRAM timing, use the specified minimum periods. The AC table requires at least 7 ns at CAS latency 3 and at least 10 ns at CAS latency 2. The 166 MHz option is a different -6 ordering code. Use the actual minimum period and clock tolerance when reviewing a design.
No. tRCD is the minimum interval from ACTIVE to READ or WRITE. CAS latency counts cycles from READ to the first output data. For the -7 grade, tRCD is at least 21 ns. The controller and SDRAM mode register must also agree on CL2 or CL3 and the permitted clock period.
No. The memory is volatile and needs its specified refresh behavior. Normal operation requires 8192 refresh cycles in 64 ms. Self-refresh is a distinct operating mode with entry and exit requirements; ordinary clock suspension or power-down should not be treated as unlimited data retention.
For an SDR SDRAM replacement, include the exact MPN, quantity, required date, original approved code, TSOP II package, SDRAM temperature grade, controller/board revision, memory clock, CAS setting and allowed alternatives. Share the engineering timing, initialization and refresh comparison and required lot evidence. A quote does not itself approve a substitute or establish delivery availability.
By Ying Lin
AS4C16M16SA-7TCN is Alliance Memory’s 256-Mbit, 16M × 16 SDR SDRAM with a commercial 0–70°C temperature grade. Its capacity and 54-pin TSOP II package can make it look familiar in a legacy memory BOM. Approval still depends on the complete suffix, supported CAS latency, controller timing, refresh and initialization. Buyers need that engineering comparison before treating another 16M × 16 part—or a faster member of this family—as an accepted substitute.
Alliance's ordering table and suffix chart identify AS4C16M16SA-7TCN as the -7 speed grade, TSOP II package, commercial temperature option and lead-free/halogen-free version. The package has 54 leads, a nominal 400 mil body width and 0.8 mm lead pitch. A 54-ball BGA is a different package even when the family name and capacity match.
The memory uses a 3.3 V ±0.3 V supply and LVTTL interface. Its address organization has 13 row bits, nine column bits and two bank-select bits, with a 16-bit data bus. A controller profile copied from a smaller SDRAM can address only part of the device or alias addresses even when a simple read/write test appears to work.
A sound SDR SDRAM replacement comparison therefore begins with the original approved MPN, board revision and memory-controller configuration. Confirm the actual connected address lines, byte masks, chip select and clock. Do not use an inventory description calling this device DDR3, or a generic family frequency field, to override the manufacturer's exact ordering and timing tables. The public family page is a navigation and identity source; the dated datasheet remains the technical basis used here. Alliance datasheetAlliance family page
For 143 MHz SDRAM timing, start with the actual memory clock period, not the processor core frequency or a catalogue maximum. Then convert each minimum delay to a whole number of clock intervals, rounding upward. Confirm how the chosen controller encodes that count: a hardware field may store a count, a count minus one, or a constrained value dependent on other fields. This article does not prescribe a register image for an unspecified MCU or FPGA.
Figure 1: At an illustrative 100 MHz clock, the -7 grade’s 21 ns minimum tRCD needs three clock intervals. The CL3 data reference is three intervals after READ; actual data validity and board approval require the remaining datasheet and controller timing checks. Compiled by YG GROUP. Evidence: documentation 1.
Table 1: Minimum command delays at an illustrative 100 MHz clock. Source: Alliance Rev. 3.0, printed page 19; calculated intervals use a 10 ns period. Compiled by YG GROUP.
| -7 parameter | Datasheet requirement | Illustrative minimum at a 100 MHz memory clock |
|---|---|---|
| tCK | 7 ns at CL3; 10 ns at CL2 | A 10 ns period meets these clock-period minima |
| tRCD: ACTIVE to READ/WRITE | 21 ns minimum | 3 intervals = 30 ns |
| tRP: PRECHARGE delay | 21 ns minimum | 3 intervals = 30 ns |
| tRAS: ACTIVE to PRECHARGE | 42 ns minimum | 5 intervals = 50 ns |
| tRC / tRFC | 63 ns minimum | 7 intervals = 70 ns |
| tWR: write recovery | 14 ns minimum | 2 intervals = 20 ns |
The 100 MHz column is an original planning calculation using ceil(minimum time / 10 ns), not a tested configuration. Complete command sequencing, controller restrictions and board setup/hold analysis remain part of the approval.
CAS latency is a separate setting: it counts the delay from a READ command to the first output data. It is not tRCD, which sets the delay from opening a row to issuing READ or WRITE. The controller's read expectations and the SDRAM mode register must agree. Selecting CL2 because it appears faster does not permit running this -7 part at its CL3 maximum rate.
The family ordering table calls the -7 grade 143 MHz; the AC table specifies a 7 ns minimum period at CL3. Keep the period limit as the design constraint rather than rounding a clock upward to an exact catalogue label. Include clock tolerance, input setup/hold, output timing, loading and board skew in the engineering review. Passing the command-delay arithmetic alone does not prove the data capture window.
Possibly, but only after the existing initialization and operating configuration have been checked against this device. The shared organization does not prove that a borrowed controller profile, startup delay, mode word or refresh counter is suitable.
Alliance's specified power-up sequence applies power to VDD and VDDQ simultaneously with CKE low, DQM high and inputs held at NOP. Start the clock and maintain stable conditions for at least 200 µs, then bring CKE high. Precharge all banks, program the mode register and provide at least two AUTO REFRESH dummy cycles. The datasheet permits the refresh cycles before or after Mode Register Set; the required timing between commands still applies. Alliance datasheet
The default mode-register contents are undefined at power-up. Program the intended CAS latency, burst length, burst type and write-burst behavior, keep reserved fields at zero, and observe the Mode Register Set delay before proceeding. The two-clock mode-register requirement must be respected along with the speed-grade timing table. A generic 100 µs example or a mode word for another chip is not sufficient evidence.
Normal operation requires 8192 refresh cycles in 64 ms, with the AC table specifying a maximum average refresh interval of 7.8 µs. The controller must preserve that requirement while arbitrating reads, writes and precharge. Do not carry over a roughly 15.6 µs interval from a 4096-refresh device. All banks need the appropriate idle/precharged state and recovery time for AUTO REFRESH. Alliance datasheet
Review low-power behavior separately. Self-refresh preserves data using internal refresh operation under its specified entry and exit conditions. Clock suspension or power-down is not an unlimited substitute for refresh, and removing power loses the volatile contents. Confirm the controller's exit delays and refresh restoration before approving suspend/resume use.
Its specified commercial ambient range is 0–70°C. It should not be approved for a requirement extending from −40°C to +85°C simply because the shared datasheet also covers industrial parts. The SDRAM temperature grade belongs to the exact ordering code. A successful room-temperature memory test cannot extend that published rating. Alliance datasheet
If an industrial range is required, review a genuinely industrial ordering code and its complete technical requirements. Also distinguish ambient operating range from storage or absolute maximum limits. Those stress ratings are not alternate operating grades. Engineering must confirm the board environment, local heating and validation conditions rather than relying on the word “industrial” in the finished product's description.
The shared manufacturer datasheet lists two exact functional neighbors that make useful speed and temperature comparisons. These are different specified device grades, not packaging aliases. Neither is automatically added to the customer's approved vendor list.
Table 2: Same-family speed and temperature choices. Source: Alliance Rev. 3.0 ordering, AC, package and suffix tables. Compiled by YG GROUP.
| Exact ordering code | Listed maximum rate | Ambient grade | Package | Approval boundary |
|---|---|---|---|---|
| AS4C16M16SA-7TCN | 143 MHz | Commercial, 0–70°C | 54-pin TSOP II | Primary part; use its -7 timing column |
| AS4C16M16SA-6TCN | 166 MHz | Commercial, 0–70°C | 54-pin TSOP II | A faster speed grade does not add industrial temperature coverage |
| AS4C16M16SA-6TIN | 166 MHz | Industrial, −40–85°C | 54-pin TSOP II | Temperature candidate; check -6 timing, electrical limits and board approval |
Engineering approval remains specific to the controller and board configuration; the shared family table alone does not qualify a replacement.
For example, the -6 and -7 columns have different tRCD, tRP and tRFC minima, while CL2 still requires a 10 ns minimum clock period in both columns. “Faster grade” is therefore not an instruction to change one clock field and leave the rest untouched. Preserve the existing approved settings only when they satisfy the candidate's complete requirements and the controller's constraints.
A practical approval record should compare package and pin map, supply and IO levels, address geometry, CL and burst mode, all command delays, refresh policy, initialization and low-power behavior. Record each result as unchanged and verified, configuration change needed, or unsuitable. Procurement can then request the approved exact codes without making the engineering decision from availability alone.
The engineering plan should cover the full address range and all banks, data bits and byte lanes; boundary and burst behavior; repeated initialization; refresh under sustained traffic; and required power-state transitions. Review the intended voltage, temperature and clock conditions. A short test near the base address does not expose every address-line, mapping or refresh problem.
Where a host uses caches or DMA, the host's own memory-map, cache and coherency rules also need review. Those are controller and software requirements, not extra features supplied by the SDRAM. No board-level timing measurement or environmental qualification is claimed by this comparison.
For a sourcing request, send AS4C16M16SA-7TCN, quantity, required date, original approved MPN, package, board/controller revision, memory clock and CAS setting, operating temperature and the permitted alternate codes. Add the timing/initialization comparison and required lot or traceability evidence when those govern approval.
Send the exact SDRAM requirement to YG GROUP. The quotation should identify the proposed ordering code clearly; source, documentation, acceptance scope and delivery conditions require confirmation for the specific offer.