XRP7714ILB-0X14-F【PDF 17/29 页】IC REG 5OUT BCK/LINEAR 40TQFN

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Sheet目录47

13页 14页 15页 16页 [17页]18页 19页 20页 21页

?2011 Exar Corporation

17/29

Rev. 1.1.6

OVER-VOLTAGE PROTECTION (OVP)

The Over-Voltage Protection (OVP) SET_OVVP_REGISTER sets the over-voltage condition in

predefined steps per channel. The over-voltage protection is always active even during soft-start

condition. When the over-voltage condition is tripped, the controller will shut down the channel.

When the channel is shut down the controller will then set corresponding OVP Fault bits in the

READ_OVV_UVLO_OVT_FLAG register.

The VOUT OVP Threshold is 150mV to 300mV above nominal VOUT for a Voltage Target of 2.5V or

less. For the Voltage Target of 2.6V to 5.1V, the VOUT OVP Threshold is 300mV to 600mV.

Once the over-voltage Channel is disabled, the controller will check the

SET_FAULT_RESP_CONFIG_LB and SET_FAULT_RESP_CONFIG_HB to determine whether there are

any following channels that need to be shut down. Any following channel will be disabled when

the channel with the Over Voltage Fault is disabled. The channel(s) will remain disabled, until the

Host takes action to enable the channel(s).

Any of the fault and warning conditions can also be configured to be represented using the general

purpose input output pins (GPIO) to use as an interface with non I

C compatible devices. For

further information on this topic see the GPIO Pins Section.

During OVP fault shutdown of the channel, the customer has the option to choose two types of

shutdown for each channel. The first shutdown is passive shutdown where the IC merely stops

outputting pulses. The second shutdown is a brute force shutdown where the GL remains on as

the channel reaches its discharged voltage. Note that if the brute force method is chosen, then GL

will permanently remain high until the channel is re-enabled.

OUTPUT CURRENT SETTING AND MONITORING

XRP7714 utilizes a low side MOSFET Rdson current sensing technique. The voltage drop on Rdson

is measured by dedicated current ADC. The ADC results are compared to a maximum current

threshold and an over-current warning threshold to generate the fault and warning flags.

Maximum Output Current

The maximum output current is set by the SET_VIOUT_MAX_CHx register and

SET_ISENSE_PARAM_CHx register. The SET_VIOUT_MAX_CHx register is an 8 bit register. Bits

[5:0] set the maximum current threshold and bits [7:6] set the over-current warning threshold.

The LSB for the current limit register is 5 mV and the allowed voltage range is between 0 and

315mV. To calculate the maximum current limit, the user needs to provide the MOSFET Rdson. The

maximum current can be calculated as:

55B5H5G5@545K =

55`5R5[5`5R

55Q5`5\5[ ?5>5a

Where Kt is the temperature coefficient of the MOSFET Rdson; Vsense is the voltage across Rdson;

IOUTMAX is the maximum output current.

Over-Current Warning

The XRP7714 also offers an Over-Current warning flag. This warning flag resides in the

READ_OVC_FLAG register. The warning flag bit will be set when the output current gets to within a

specified value of the output current limit threshold enabling the host to reduce power

consumption. The SET_VIOUT_MAX_CHx register allows the warning flag threshold to be set 10mV,

20mV, 30mV or 40mV below VIOUT_MAX. The warning flag will be automatically cleared when the

current drops below the warning threshold.

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