FAN2558 Datasheet, PDF (6/12 Pages) Fairchild Semiconductor – 180mA Low Voltage CMOS LDO

APPLICATIONS INFORMATION
Test Reference and Output Termination
The MC100ES8111 is designed for high-frequency and
low-skew clock distribution. The high-speed differential
outputs are capable of driving 50 Ω transmission lines and
always require a DC termination to V_TT (GND). In order to
maintain the tight skew and timing specifications, it is
recommend to terminate the differential outputs by 50 Ω to
GND, with the termination resistor located as close as
possible to the end of the clock transmission line. All DC and
AC specifications apply to this termination method (see the
reference circuit shown in Figure 3 “MC100ES8111 AC Test
Reference”). The MC100ES8111 does not support an output
termination to V_TT = V_X = 0.75 V (center voltage termination).
V_CC = 3.3 V ± 5%
V_CCO = 1.8 V ± 0.1 V or 1.5 V ± 0. 1 V
Differential Pulse
Generator
Z = 50 Ω
Z = 50 Ω
Z = 50 Ω
R_T = 50 Ω
DUT
MC100ES8111
R_T = 50 Ω
V_TT = GND
V_TT = GND
Figure 3. MC100ES8111 AC Test Reference
Oscilloscope
or Tester
Power Consumption and the Junction Temperature
The power consumption P_TOT of the MC100ES8111
depends on the supply voltages and the DC output
termination. The clock frequency has a negligible effect on
P_TOT. If all outputs are terminated by 50 Ω to GND, the device
power consumption is calculated by:
P_TOT = V_CC · I_CC + I_CCO · (V_CCO - V_X)
For instance, at a supply voltage of V_CC = 3.3 V and a
termination of 50 Ω to GND, the typical device power
consumption is 579 mW at V_CCO = 1.8 V and 474 mW at
V_CCO = 1.5 V.
Table 7. Power Consumption
MC100ES8111
P_TOT,
(1)
TYP
P_TOT,
(2)
MAX
V_CCO = 1.5 V
470 mW
647 mW
V_CCO = 1.8 V
575 mW
769 mW
1. Typical case: V_CC, V_CCO at nominal values and using typical
I_CC, I_CCO data.
2. Worst case: V_CC, V_CC at max. values and using max. I_CC, I_CCO
limits.
To make the optimum use of high clock frequency and low
skew capabilities of the MC100ES8111, the device is
specified, characterized and tested for the junction
temperature range of T_J = 0°C to +110°C. Because the exact
thermal performance depends on the PCB type, design,
thermal management and natural or forced air convection,
the junction temperature provides an exact way to correlate
the application specific conditions to the published
performance data of this datasheet. The correlation of the
junction temperature range to the application ambient
temperature range and vice versa can be done by
calculation:
T_J = T_A + R_thja · P_tot
Assuming a thermal resistance (junction to ambient) of
54.4°C/W (2s2p board, 100 ft/min airflow, see Table 8) and a
typical power consumption of 575 mW (all outputs terminated
50 ohms to GND, V_CCO = 1.8 V), the junction temperature of
the MC100ES8111 is approximately T_A + 31°C, and the
minimum ambient temperature in this example case
calculates to -31°C (the maximum ambient temperature
is 79°C. See Table 8). Exceeding the minimum junction
temperature specification of the MC100ES8111 does not
have a significant impact on the device functionality.
However, the continuous use the MC100ES8111 at high
ambient temperatures requires thermal management to not
exceed the specified maximum junction temperature.
Table 8. Ambient Temperature Ranges (P_tot = 575 mW)
R_thja (2s2p board)
T_A,
(1)
min
T_{A, max}
Natural convection 59.0°C/W
-34°C
76°C
100 ft/min
54.4°C/W -31°C
79°C
200 ft/min
52.5°C/W -30°C
80°C
400 ft/min
50.4°C/W -29°C
81°C
800 ft/min
47.8°C/W -27.5°C
82.5°C
1. The MC100ES8111 device function is guaranteed from
T_A = -40°C to T_J = 110°C.
Maintaining Lowest Device Skew
The MC100ES8111 guarantees low output-to-output skew
of max. 80 ps and a part-to-part skew of max. 630 ps
(V_CCO = 1.8 V). To ensure low skew clock signals in the
application, both outputs of any differential output pair need
to be terminated identically, even if only one output is used.
When fewer than all ten output pairs are used, identical
termination of all output pairs within the output bank (same
package side) is recommended. If an entire output bank is not
used, it is recommended to leave all of these outputs open
and unterminated. This will reduce the device power
consumption while maintaining minimum output skew.
MC100ES8111
6
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