February 12, 2009

Sanken Develops 2-Phase Stepping Motor Unipolar Driver IC
- Featuring a multi-chip structure in a surface-mount package -

Sanken Electric Co., Ltd. announced the development of the SI-7321M, a 2-phase stepping motor unipolar driver IC. The SI-7321M has an output current of 1.5 A and features a multi-chip structure in a surface-mount package that can be auto-mounted. Samples of the SI-7321M are now available at a price of 800 yen per unit (tax excluded). Mass production starting at 10,000 units is scheduled for March 2009, with the production scale increasing to 50,000 units per month from April 2010.
1. Development Background and Product Overview
  Two-phase stepping motors are commonly used in devices such as the paper feeders of copiers and the card readers of ticket-vending machines and ATMs, most of these stepping motors are driven by unipolar driver ICs. Today’s motor driver PC boards must be slim to comply with the device’s internal structural constraints. Demand is therefore increasing for unipolar driver ICs to be surface mounted and low profile to enable auto-mounting and raise board assembly productivity.

Most unipolar driver ICs on the market have a multi-chip structure (one controller and 4 MOSFETs) and are housed in a through-hole type package. These packages can be made slimmer by bending the leads of the components so that they are lying down, but they cannot be auto-mounted. Monolithic surface-mounted unipolar driver ICs do exist, but their monolithic structure gives rise to a high on-resistance and they generate considerable heat, requiring the attachment of a large heat sink.

However, by developing a new type of lead frame, Sanken has overcome these problems and produced the SI-7321M, a 2-phase stepping motor unipolar driver IC that has a multi-chip structure in a surface-mount package.

The surface-mount package of the SI-7321M enables auto-mounting and gives it a 50% lower profile than previous driver ICs. Also, by using a MOSFET with a low on-resistance, the power dissipation has been cut by 50% compared to monolithic ICs.
2. Features
(1) One controller and 4 MOSFETs in a surface-mount package (HSOP40)
Dimensions of resin part: 18.6 × 7.5 × 2.2 mm
(2) Supports a wide range of step sizes, from full-step driving to 1/16th microstep driving.
(3) Motor driving is controlled by a clock pulse.
(4) Open-load and short-circuit failure protection circuits
The SI-7321M includes features to protect the device from open-load (motor coil disconnection) and short-circuit failures. A fail signal can also be output during operation. These features enhance reliability by preventing damage to an IC that is operating abnormally.
(5) Protection features can be used as needed.
Whether or not to use a certain protection feature can be easily specified in accordance with the requirements of the SI-7321M’s application.
(6) Sleep mode
The SI-7321M can be set to sleep mode, in which only 5% of active-mode power is consumed.
3. Applications
  Printers, copiers, ticket-vending machines, ATMs, industrial robots, etc.
4.  Specifications Overview
Parameter Symbol Rating Unit
Main power supply voltage VBB 10 to 44 V
Logic power supply voltage VDD 3.3 to 5.5 V
Output current IO 1.5 A
Output MOSFET on-resistance RDS(ON) 0.25 Ω
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