MAX14895E Datasheet, PDF (8/11 Pages) Maxim Integrated Products – Enhanced VGA Port Protector DDC Outputs have Internal Pullups

MAX14895E
Enhanced VGA Port Protector
Detailed Description
The MAX14895E integrates level-translating buffers and
features RED, GRN, and BLU port protection for VGA sig-
nals. Horizontal and vertical synchronization (SYNCH0,
SYNCV0) inputs feature level-shifting buffers to support
low-voltage CMOS or standard TTL-compatible graphics
controllers. Each output can drive Q10mA and meets
VESA specifications. The device also features I²C level
shifting using two nMOS devices.
The device generates its own internal bias supply to
clamp SCL0 and SDA0 to a safe level, removing the need
for another external supply. The device also provides a
current-limited V_CC output with power-off protection. This
output can be used to switch power to a VGA connector
or the VGA interface of a monitor.
Horizontal/Vertical Sync Level Shifter
SYNCH0 and SYNCV0 are buffered to provide level shift-
ing and drive capability to meet the VESA specification.
The level-shifted outputs (SYNCH1, SYNCV1) are pulled
low when EN is low and EN is high, or when the device
is in thermal shutdown (see the Functional Diagram/
Truth Table). Logic-level outputs (V_OL, V_OH) are 5V TTL-
compatible. These two buffers are identical and each
can drive either the horizontal or the vertical synch signal.
Display Data Channel Switches
The device incorporates two nMOS switches for I²C
level shifting. The SDA0 and SCL0 terminals are voltage
clamped to a diode drop less than the internal V_L volt-
age. Voltage clamping provides protection and compat-
ibility with the SDA0 and SCL0 signals and low-voltage
ASICs. When power is off (V_CC = 0V), SDA1 and SCL1
are protected against reverse-leakage current up to V_S =
+5.25V. The SDA_ and SCL_ switches are identical, and
each switch can be used to route SDA_ or SCL_ signals.
RGB Ports
The device includes three terminals for RED, GRN, and
BLU signals. These terminals provide high-level ESD pro-
tection to the RGB lines while keeping the capacitance
on the RGB lines to a minimum. The RED, GRN, BLU
terminals are identical, and any of the three terminals
can be used to protect red, green, or blue video signals.
EN, EN
The device has dual complementary EN and EN enable
inputs and can accept either active-low or active-high
enable signals. Pull EN low and EN high to place the device
in shutdown (see the Functional Diagram/Truth Table).
V_S Output
The device provides a current-limited voltage on V_S when
the part is enabled. V_S is used as the pullup voltage for
internal pullup resistors on SDA1 and SCL1, and can be
used as an external supply. The internal pullup resistors
from SDA1 and SCL1 to V_S are active when the device is
enabled, and are disabled when the device is in thermal
shutdown (see the Functional Diagram/Truth Table).
The V_S supply includes an internal resistor to discharge
the supply when the device is in thermal shutdown or is
disabled (see the Functional Diagram/Truth Table). V_S is
current limited to prevent damage to host devices. When
power is off (V_CC = 0V), V_S is protected against reverse-
leakage current up to V_S = +5.25V.
Thermal Shutdown
Thermal-shutdown circuitry protects the device from
overheating. The device enters thermal shutdown when
the junction temperature exceeds +150NC (typ) and
returns to normal operation when the temperature drops
by approximately +10NC (typ) below the thermal-shut-
down threshold. When the device is in thermal shutdown,
both SYNCH1 and SYNCV1 are pulled down to ground,
the I²C level shifters are disabled, the SDA1 and SCL1
pullups are off, and the V_S discharge resistor is on (see
the Functional Diagram/Truth Table).
Applications Information
Power-Supply Decoupling
Bypass V_CC and V_S to ground with 1FF ceramic capaci-
tors as close as possible to the device.
PCB Layout
High-speed switches such as the MAX14895E require
proper PCB layout for optimum performance. Ensure that
impedance-controlled PCB traces for high-speed signals
are matched in length and are as short as possible.
Connect the exposed pad to a solid ground plane.
ESD Protection
As with all Maxim devices, ESD protection structures
are incorporated on all terminals to protect against elec-
trostatic discharges encountered during handling and
assembly. Additionally, the device is protected to Q15kV
on the RED, GRN, BLU, EN, V_S, SYNCH1, SYNCV1,
SCL1, and SDA1 terminals by the HBM. For optimum
ESD performance, bypass V_CC to ground with a 1FF
ceramic capacitor.
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