COSINE Tier-1 distributor Jarwey｜PWM controller supply above 28 V: COS3842BD stops, COS3525ADW lists 35 V

Jarwey is a COSINE Tier-1 distributor and can help with the shortlist, the datasheet, samples, small lots, and the delivery date.

COS3842BD is the peak-current PWM controller. The product page lists Vin max 28 V, an SOP-8 package, and Buck, Boost, Flyback, and Forward with an external FET. The same page names adapter supplies, voltage converters, and e-bike chargers. COS3525ADW is the voltage-mode PWM controller. The product page lists Vin max 35 V, a WSOP-16 package, plus soft-start and sync pins. The same page names adapter supplies, voltage converters, welders, and inverters.

Probe the controller supply pin. The external MOSFET drain is another node. A high voltage on that drain does not change the Vin max printed on the controller page.

The UC3842 / SG3525 topology table, the heat split between COS3842BD and the 3 A / 7.5 A LDOs, and the split between COS3842BD and the isolated push-pull driver COS6501 are already published. The isolated-rail article already listed 28 V as one check. This page only answers the case where the controller pin itself can rise past 28 V. Neither product page carries a datasheet — contact Jarwey for the datasheet. UC3842 and SG3525 are anchors to verify on the bench.

Supply ceiling

SOP-8 and WSOP-16 do not share a footprint. Absolute maximum and recommended operating range come from the datasheet Jarwey sends. The Vin max on the product page is the selection gate; freeze the BOM after that datasheet is in hand.

Three readings

The pin stays at or below 28 V

A 12 V auxiliary, or a regulated bias, that stays at or below 28 V through maximum line and startup overshoot is inside both page limits. A single-switch Buck, Boost, Flyback, or Forward for an adapter or an e-bike charger points to COS3842BD. A circuit that needs the soft-start and sync pins, or a welder or inverter, points to COS3525ADW. Topology choices stay in the published PWM controller family note.

The pin can exceed 28 V and stays within 35 V

Take COS3842BD off this socket. COS3525ADW is the controller whose page lists Vin max 35 V. Still read absolute maximum against the recommended range in the datasheet, and confirm the loop is voltage-mode and that the soft-start and sync pins are actually used. The WSOP-16 does not land on the SOP-8 pads.

The pin can exceed 35 V

Neither product page supports tying that rail straight to the controller. Build a lower bias for the chip, then return to the PWM choice. The MOSFET drain may sit higher. That node is selected with the power stage, on its own.

Where to put the probe

Put the probe on the controller supply pin. Capture maximum line, the startup edge, and a load step. A rail marked 24 V on an industrial board or a welder control supply may cross 28 V once tolerance is included, or it may stay under. Use the measured peak. The nominal label is the wrong number for this socket.

Checklist before the BOM

1. Two nodes: record the peak on the controller supply pin and the peak on the MOSFET drain.
2. Past 28 V: if the controller pin can exceed 28 V, remove COS3842BD from this socket.
3. Past 35 V: if the controller pin can exceed 35 V, do not hang COS3525ADW on it either. Drop the bias first.
4. Inside 28 V: when both parts can be powered, pick topology and the sync pin from the family note.
5. Footprint: lay out SOP-8 and WSOP-16 as separate land patterns.
6. Anchors: check UC3842 and SG3525 against the datasheet and samples before the BOM is frozen.
7. Datasheet and delivery: contact Jarwey for the datasheet, samples, a small lot, and the delivery date.

Product pages

• COS3842BD — peak-current PWM, Vin max 28 V, SOP-8
• COS3525ADW — voltage-mode PWM, Vin max 35 V, WSOP-16, soft-start and sync pins

Send Jarwey the measured peak on the controller pin, the topology, and the part number in use: kerry.w@jarwey.cn · Contact.