X

0

Q

© 2012 Exar Corporation

14/28

Rev. 1.2.2

Fig. 190: VCCA (green) Startup Waveform

This 100mA low drop-out regulator can be programmed as 3.3V or 5V in SET_STBLDO_EN_CONFIG

register. Its output is seen on the LDOOUT Pin. This LDO is fully controllable via the Enable Pin

The standby LDO should be bypassed with a minimum of 2.2uF ceramic capacitor.

The XRP7708 is enabled via raising the ENABLE Pin high. The chip can then be disabled by

SOFTRESET Command.

For enabling a specific channel, there are several ways that this can be achieved. The chip can be

configured to enable a channel at start-up as the default configuration residing in the non-volatile

Bus serial command. The registers that control the channel enable functions are the

SET_EN_CONFIG and SET_CH_EN_I2C.

The XRP7708 integrates Internal Gate Drivers for all 4 PWM channels. These drivers are optimized

to drive both high-side and low side N-MOSFETs for synchronous operation. Both high side and low

side drivers have the capability of driving 1 nF load with 30 ns rise and fall time. The drivers have

built-in non-overlapping circuitry to prevent simultaneous conduction of the two MOSFETs.

While the chip is operating there are four different types of fault handling:

•

Under Voltage Lockout (UVLO) monitors the input voltage to the chip, and the chip will

shutdown all channels if the voltage drops to critical levels.

•

Over Temperature Protection (OTP) monitors the temperature of the chip, and the chip

will shutdown all channels if the temperature rises to critical levels.

•

Over Voltage Protection (OVP) monitors the voltage of channel and will shutdown the

channel if it surpasses its voltage threshold.