Technical Note

8/24

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2011.06 - Rev.A

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BD4157MUV

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Description of block operation

EN

With an input of 2.0 volts or higher, this terminal goes HIGH to activate the circuit, and goes LOW to deactivate the circuit

(with the standby circuit current of 40 μA), It discharges each output and lowers output voltage when the input falls to 0.8

volts or less.

V3_IN, V15_IN, and V3AUX_IN

These are the input terminals for each channel of a 3ch switch. V3_IN and V15_IN terminals have two pins each, which

should be short-circuited on the pc board with a thick conductor. A large current runs through these three terminals :

(V3_IN: 1.3A; V3AUX_IN: 0.275 A; and V15_IN: 0.65 A). In order to lower the output impedance of the connected power

supply, it is recommended that ceramic capacitors (with B-type characteristics or better) be provided between these

terminals and the ground. Specifically, the capacitors should be on the order of 1 μF between V3_IN and GND, and

between V15_IN and GND; and on the order of 0.1 μF between V3AUX_IN and GND.

V3, V15, and V3AUX

These are the output terminals for each switch. The V3 and V15 terminals have two pins each, which should be

short-circuited on the PC board and connected to an ExpressCard connector with a thick conductor, as short as possible.

In order to stabilize the output, it is recommended that ceramic capacitors (with B-type characteristics or better) be

provided between these terminals and the ground. Specifically, the capacitors should be on the order of 10 μF between V3

and GND, and between V15 and GND; and on the order of 1 μF between V3AUX and GND.

CPPE#

This pin is used to find whether or not a PCI-Express signal compatible card is present. Turns to “High” level with an

input of 2.0 volts or higher, which means that no card is provided, while it turns to “Low” level when the input is lowered to

0.8 volts or less, which means that a card is provided. Controls the ON/OFF, switch selecting the proper mode based on

the status of the system. Pull up resistance (100kΩ～200kΩ) is built into, so the number of components is reduced.

CPUSB#

This pin is used to find whether or not a USB2.0 signal compatible card is present. Turns to “High” level with an input of

2.0 volts or higher, which means that no card is provided, while it turns to “Low” level when the input is lowered to 0.8 volts

or less, which means that a card is provided. Controls the ON/OFF switch, selecting the proper mode based on the

system status. Pull up resistance (100kΩ～200kΩ) is built into, so the number of components is reduced.

SYSR

This pin is used to detect the system status. Turns to “High” level with an input of 2.0 volts or higher, which means that

the system is activated, while it turns to “Low” level when the input is lowered to 0.8 volts or less, which means that the

system is on standby.

PERST_IN#

This pin is used to control the reset signal (PERST#) to a card from the system side. (Also referred to as “SysReset#” by

PCMCIA.) Turns to “High” level with an input of 2.0 volts or higher, and sets PERST# to “High” AND with a “Power Good”

output. Turns to “Low” level and sets PERST# to “Low” when the input falls to 0.8 volts or less.

PERST#

This pin is used to send a reset signal to a PCI-Express compatible card. Reset status is determined by the outputs,

PERST_IN#, CPPE# system status, and EN on/off status.

Turns to “High” level and activates the PCI-Express

compatible card only if each output is within the “Power Good” threshold, with the card inserted and PERST_IN# turned to

“High” level.

RCLKEN

This pin is used to send an enable signal to the reference clock. Activation status is determined by the outputs, CPPE#

system status, and EN on/off status. Turns to “High” level and activates the reference clock PLL only if each output is

within the “Power Good” threshold, with the card kept inserted.

TEST

This pin is used to test, which should be short-circuited to the GND. When it is short-circuited to V3AUX_IN, UVLO

(V3_IN, V15_IN) turns OFF.