July 10, 2007

Step-down Switching Regulator IC with Current Mode Control employed SI-8005Q
Regulator circuitry can be downsized to 50% of the conventional circuitry

Sanken Electric Co., Ltd. has development and started sample shipments of the SI-8005Q, a step-down switching regulator IC, employing a current mode control system (see the end "Note") that allows to downsize the regulator circuitry approximately 50% of the conventional one.  While using a compact HSOP8 package, the SI-8005Q allows to supply the output current of 3.5 A and the output voltage is variable from 0.5 to 24 V.  This IC is the first product to use a die developed in collaboration with Polar Semiconductor, Inc. (PSI) in the USA, a subsidiary that Sanken Electric acquired two years ago.  Sanken provided PSI with the electrical specifications of the die, and PSI executed the circuit and layout designs, and die manufacturing using its proprietary BCD process.

The IC will be launched in October, CY07 starting with 100k pcs/month, then ramping up to 1,000k/month in March, CY08. (Sample price: 400 Yen.)
1. Development background and product overview
  These days, signal-processing ICs such as microcomputers and DSPs used in various electronic devices are seeing their operating voltages decrease as the devices become more power-saving and, at the same time, power supply voltages become more diverse.  Furthermore, since the mounting-component count is increasing as the devices are downsized, thinned and sophisticated, the more compact circuit boards for mounting ICs are strongly demanded, thus resulting in demands for reducing the areas occupied by regulator circuitries on the boards.

Sanken has therefore developed the SI-8005Q step-down switching regulator IC, which employs a current mode control system that permits compact ceramic capacitors to be used as output capacitors.

The power loss of SI-8005Q is reduced by controlling the maximum on-resistance of a built-in output MOS FET as low as 165 mΩ.  Furthermore, die miniaturization could be achieved by using a BCD process, allowing it to be mounted in a compact surface mount package (HSOP8), resulting in the size of about one-fourth (the footprint of the resin portion) the size of Sanken's conventional product. In sum, Sanken has realized to reduce by about 50% the area occupied by the regulator circuitry in the circuit board compared with Sanken's conventional circuitries.

Since the output voltage is variable from 0.5 V, it can be easily set to the voltage compatible with today’s trend of reduced power supply voltages for signal processing ICs.  What’s more, since the input voltage range is as wide as from 4.75V to 28V, direct drive by 24V power supply system is possible.
2. Major applications

Power supplies for signal processing ICs such those for memories and microcomputers used in plasma display panel (PDP) TVs, liquid crystal display (LCD) TVs, HDD and DVD recorders, and other devices.

3. Features
a. Current mode control system employed
-Compact ceramic capacitors with low resistance can be used, allowing the size of the regulator circuitry to be reduced to about 50% compared to Sanken's conventional circuitries.
b. Excellent line regulation (max.: 60 mV)
c.  Maximum 165 mΩ on-resistance of built-in MOS FET
-Employing a compact surface mount HSOP8 (with back-side heat sink) package, output current is 3.5 A.
d.  Wide range of input voltages (4.75 to 28 V)
-Direct drive by 24 V power supply system possible
e. Output voltages (0.5 to 24 V)
-Compatible with various IC power supply voltages, thanks to a low reference voltage of 0.5 V.
f. High efficiency
-94%, maximum (when Vin = 8 V, Vo = 5 V, Io = 0.5 A)
g. Operation frequency of 500 kHz
-Smoothing choke coil can be downsized.
h. Diverse built-in protection functions
-Drooping type overcurrent protection
-Overheat protection
i.  Included functions
  -Built-in soft-start
-Built-in output on/off
-Built-in under voltage lockout (UVLO)
Parameter SI-8005Q SI-8000FD
(Conventional product,
as a reference)
Input voltage range 4.75 to 28 4.5 to 43 V
Output current 3.5 3.5 A
Output voltage range 0.5 to 24 0.8 to 24 V
Operating frequency 500typ 300typ kHz
Circuit current when off 20max 600max μA
Efficiency 90typ 83typ %
Line regulation 60max 80max mV
Load regulation 60max 50max mV
Package (resin dimensions) HSOP8(5.2×4.4×1.5) TO263-5(10×9.2×4.5) mm
  Note: Current mode control system ---- One type of the system controlling the output voltage variation.

Conventional system: voltage mode control
This is a system for stabilizing the output voltage by feeding back the output voltage variations to the IC.  Due to the circuit configuration, this system is subject to such abnormal oscillations as the phenomenon that for example, the output voltage varies because the switching operation becomes unstable. In order to control this problem, electrolytic capacitors with high resistance and high capacity need to be used as output capacitors.

  New system: current mode control
This is a system which stabilizes output voltage by feeding back to the IC the variations of output current as well as output voltage.  Thanks to the circuit configuration, the abnormal oscillations do not occur unlike the voltage mode control system. Therefore, compact ceramic capacitors with low resistance can be used as output capacitors.
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