LMH2190 Datasheet, PDF (17/32 Pages) National Semiconductor (TI) – Quad Channel 27 MHz Clock Tree Driver with I2C Interface

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LMH2190
SNAS473H – JUNE 2009 – REVISED MAY 2013
CLK_REQx INPUT POLARITY
REG0x-Bit2
CLK_REQx_FORCE ON
REG0x-Bit3
CLK_REQx
1
CLKx ENABLE
CLK_REQx INPUT VALUE
REG05-Bitx
200 kÖ
CLK_REQx_FORCE OFF
REG0x-Bit4
CLK_REQx PULL DOWN RESISTOR
REG0x-Bit5
Figure 23. Clock Request Input
System Clock Request Output
In the typical mode of operation, the clock request output will be enabled if one of the 4 CLK_REQ inputs is high
(Figure 24). However, this can be overridden via the I²C interface which has a register bit that forces the output
to be enabled, independent of the CLK_REQ input. The polarity of the output can be controlled via I²C
(CLK_REQ Output Polarity) along with whether the output is configured as push/pull, open drain or open source.
For the open drain case, there needs to be an external resistor that pulls the SCLK_REQ to a high level. This
high level may be greater than the LDO voltage of 1.8V, but not more than the supply voltage (V_BAT) of the
LMH2190.
CLK_REQ OUTPUT TYPE
REG00-Bit1
CLK_REQ OUTPUT POLARITY
REG00-Bit2
V_{DD_IO}
CLKx_ENABLE
0
1
CLK_REQ OUTPUT MODE
REG00-Bit3
SCLK_REQ
SCLK_REQ OUTPUT VALUE
REG05-Bit5
Figure 24. System Clock Request Output
The System Clock Request Output pin can be used to enable or disable an external TCXO to save power
consumption. See Figure 25. The LDO powers the TCXO, while the SCLK_REQ enables or disables the TCXO.
If the TXCO doesn't have an enable pin, power savings can be realized by switching off the LMH2190's LDO and
therewith the TCXO.
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