Si9143

Features:

• Automatic True Current Sharing with Parallel Converters
• External SCR Drive for Fault Protection
• Over-Voltage Protection
• Programmable Over-Current Protection
• Voltage Mode Control
• Precision 1.3-V, ±1.6% Reference
• Drives N-Channel Switch and Rectifier
• 800-µA Quiescent Current (fs = 200 kHz)
• 150-µA Standby Current
• Integrated "Power Good" Output
• Synchronization
• Under-Voltage Lockout


Application

Current Sharing

The Si9143 is designed to permit true load current sharing between multiple paralleled voltage-mode controllers. Traditional voltage-mode controllers do not support load sharing at all-the controller with the highest output voltage will attempt to provide all the load current. Even current-mode controllers do not properly share unless their error amps are
tied together.

The Si9143 is a new concept in current sharing (Pat. Pend.) that works by forcing the duty cycles of multiple controllers to be identical. This is accomplished by tieing together the PWM and SYNCH pins of all the controllers. The SYNCH pins force each controller to start their duty cycle at the same time, which is to say that they all run at the same frequency and phase; the controller with the highest frequency controls all of the others. The PWM pins force each controller to finish their duty cycle at the same time, causing them to have exactly equal duty cycles; the controller with the smallest duty cycle controls all of the others.

The current that each converter delivers will thus be 1/N of the total current, if there are N total converters in parallel. Limitations to this scheme are dependent primarily on matching of the resistances in the converter: mismatch in resistance results in one converter delivering more current than another. However, this effect is minor for practical converter designs, and typical current sharing may be expected to be within 10%.

Paralleling and Redundancy

The Si9143 is specifically designed for paralleling converters, meaning that multiple converters run from the same power source and deliver power to the same output bus (see Figure 4). The typical reason for such an arrangement is a limitation in how much power a single converter is able to deliver. The limitations are often thermal, and arise for example from finite on-resistance of available MOSFETs, causing them to self-heat. More power cannot then be derived


Pinout




Specifications

Voltages Referenced to AGND
V_{SYNC_IN} . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  . . .-0.3 to 7 V
V_{SYNC_OUT}. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . .-0.3 to 7 V
V_CC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  . .-0.3 to 15 V
Voltages Referenced to PGND
V_BST . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .-0.3 to 20 V
V_PGND to V_AGND. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ±2 V
V_L Short to G_ND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . Continuous
V_REF Short to G_ND . . . . . . . . . . . . . . . . . . . . . . . . . . . ... . . Continuous
V_SUPPLY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  . .-0.3 to 15 V
Continuous Power Dissipation (T_A = 25°C)a
24-Pin SSOPb . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2 W
Operating Temperature Range . . . . . . . . . . . . . . . . . . .  . . .0 to 70°C
Storage Temperature Range . . . . . . . . . . . . . . . . . . . . . -65 to 125°C
Lead Temperature (soldering, 10 sec). . . . . . . . . . . . . . .. . . . . 300°C
T_JMAX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150°C
_JA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 104°C/W
Notes
a. Device mounted with all leads soldered or welded to PC board.
b. Derate 9.6 mW/°C above 25°C.


Description

The voltage mode, synchronous buck controller is designed for point-of-use dc/dc conversion in high performance server and desktop computers. High efficiency is accomplished at full load by driving high- and low-side n-channel MOSFETs. The input voltage range has been designed for 4.75 V to 13.2 V to allow use of either 5 V or 12 V. The 1-MHz switching
frequency combined with the 10-MHz error amplifier provides ultra-fast transient response necessary in a high performance microprocessor power supply.

Si9143 is designed to provide automatic true current sharing with parallel power supplies. True current sharing reduces stress on a single supply and increases system reliability. The system reliability is further increased by short circuit protection and external SCR drive signal to disconnect the power supply during fault conditions.

Si9143 is available in a wide-body 24-pin SSOP package and specified to operate over the commercial (0° to 70°C) temperature range.

A demo board, Si9143DB, is available.