XRP7740ILB-0X18-F【PDF 14/28 页】IC REG 5OUT BCK/LINEAR 40TQFN

?2012 Exar Corporation

14/28

Rev. 1.2.2

Fig. 190: VCCA (green) Startup Waveform

STANDBY LOW DROP-OUT REGULATOR

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

(configured to turn on as soon as power is applied), a GPIO, and/or I

C communication.

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

ENABLING, DISABLING AND RESET

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

lowering the same ENABLE Pin. There is also the capability for resetting the Chip via an I

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

configuration memory of the IC. The channels can also be enabled using GPIO pins and/or an I

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

SET_EN_CONFIG and SET_CH_EN_I2C.

INTERNAL GATE DRIVERS

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.

FAULT HANDLING

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.

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