August
30, 2004, Taipei, Taiwan –– System General
Corporation (SG), today announced a new addition to
its Green Mode PWM IC series—the SG6846. The
SG6846 comes with an AC input brownout protection,
a two-level over current protection (OCP), latch circuits
for protection functions such as OCP, over temperature
protection (OTP), and over voltage protection (OVP).
All these features make it an ideal solution for motor
driving applications that need switching mode power
supplies with surge-current output.
Provides Excellent Protection
Incorporated with a two-level OCP function, the SG6846
provides excellent protection from over current. On
level one, the SG6846 provides cycle-by-cycle current
limiting with line compensation to ensure a constant
output current. On level two, when the switching current
becomes higher than two thirds of the peak-current
threshold for longer than 96 milliseconds, the over-current
protection activates causing the SG6846 to shut down.
There are several other protection functions. AC input
brownout protection with hysteresis ensures safe operation
during line disturbances. PWM output is disabled as
long as VDD voltage exceeds 23.6V. The gate output
is clamped at 18V to protect the power MOS from over-voltage
damage. An external NTC thermistor can be applied
to sense the ambient temperature for over-temperature
protection. When OTP, OCP, or VDD over voltage faults
are detected, an internal latch circuit is used to
latch-off the controller. The latch resets only when
the AC plug is removed.
Enhances the Performance of Flyback Converters
The highly integrated SG6846 series of PWM controllers
provide several features to enhance the performance
of flyback converters. To minimize standby power consumption,
a patented off-time modulation technology continuously
decreases the switching frequency under light-load
conditions. Under zero-load conditions, the power
supply enters burst-mode. This green-mode function
enables the power supply to easily meet international
power conservation requirements.
Improves Standby Power Consumption
To further improve standby power consumption, the
SG6846 series is manufactured using the BiCMOS process.
This allows the start-up current to be reduced to
8uA, and the operating current to be reduced to 3.7mA.
A higher start-up resistance can be used to improve
power saving.
Built-in synchronized slope compensation ensures the
stability of peak-current-mode control. Proprietary
internal compensation ensures constant output power
limiting over a range of AC input voltages from 90VAC
to 264VAC.
Features Summary
- Two-level OCP with 96ms delay time
- Peak-current-mode operation with cycle-by-cycle
current limiting
- PWM frequency continuously decreasing with burst
mode at light loads
- Low start-up current (8uA)
- Low operating current (3.7mA)
- VDD over-voltage protection (OVP)
- AC input brownout protection with hysteresis
- Programmable over-temperature protection (OTP)
- Constant power limit over universal AC input range
- Internal latch circuit for OTP, OVP, OCP
- Very few external components
Applications
General-purpose switch mode power supplies and flyback
power converters, including:
- Power adapters
- Open-frame Switching Mode Power Supply (SMPS)
- Specifically suited for an SMPS with surge current
output, such as a printer, scanner, or motor driver
Package
The SG6846 comes in two 8-pin DIP-8, and SOP-8 packages.
Lead-free packages are also available.
Availability: Now.
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