LMH2191
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SNAS485D – JULY 2010 – REVISED MAY 2013
LMH2191 Dual Channel 52 MHz Clock Tree Driver
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FEATURES
DESCRIPTION
•
•
•
•
•
•
•
The LMH2191 is a dual-channel clock tree driver that
supplies a digital system clock to peripherals in
mobile handsets or other applications. It provides a
solution to clocking issues such as limited drive
capability for fanout or longer traces. It also provides
protection of the master clock from varying loads and
frequency pulling effects, isolation from noisy
modules, and crosstalk isolation. It has very low
phase noise which enables it to drive sensitive
modules such as Wireless LAN and Bluetooth.
1
2
•
•
•
•
One Input Clock, Two Output Clocks
1.8V Square Wave Clock Outputs
Inverted Clock Outputs
Independent Clock Requests
High Isolation of Supply Noise to Clock Input
High Output-to-Output Isolation
Integrated 1.8V Low-Dropout Regulator
– Low Output-Noise Voltage
– 10 mA Load Current
EMI Filtering
Ultra Low Standby Current
VBAT Range = 2.5V to 5.5V
8-Bump DSBGA Package
The LMH2191 can be clocked up to 52 MHz and has
an independent clock request pin for each clock
output which allows the peripheral to control the
clock. It features an integrated LDO which provides
an ultra low-noise voltage supply with 10 mA external
load current which can be used to supply the TCXO
or other clock source. The LMH2191 dual clock
distributor is offered in a tiny 1.61 mm x 1.063 mm 8bump DSBGA package. Its small size and low supply
current make it ideal for portable applications.
APPLICATIONS
•
•
Mobile Handsets
Portable Equipment
Typical Application
VBAT
VBAT
CBAT
1 µF
A1
VOUT
LMH2191
B1
1.8V LDO
COUT
VDD
CCLK
10 nF
Clock
Source
A2
2.2 µF
SCLK_IN
C1
CSERIES
Clock
Tree
Driver
CLK1
Peripheral
D2
CLK2
Peripheral
B2
Clock
Request
CLK_REQ1
C2 CLK_REQ2
D1
VSS
1
2
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
All trademarks are the property of their respective owners.
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
Copyright © 2010–2013, Texas Instruments Incorporated
LMH2191
SNAS485D – JULY 2010 – REVISED MAY 2013
www.ti.com
These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
ABSOLUTE MAXIMUM RATINGS (1) (2)
VBAT - VSS
Supply Voltage
LVCMOS port IO voltage
Human Body Model
ESD Tolerance
(3)
Machine Model
Output Short Circuit Duration (4)
-0.3V to 6V
-0.3V to (VOUT + 0.3V)
2000V
200V
Charge Device Model
1000V
LDO
infinite
Clock Output
infinite
For Soldering Information see http://www.ti.com/lit/SNOA549
−65°C to 150°C
Storage Temperature Range
Junction Temperature
(1)
(2)
(3)
(4)
(5)
(5)
150°C
Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for
which the device is intended to be functional, but specific performance is not specified. For specifications and the test conditions, see
the Electrical Characteristics Tables.
If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/ Distributors for availability and
specifications.
Human body model, applicable std. MIL-STD-883, Method 3015.7. Machine model, applicable std. JESD22–A115–A (ESD MM std of
JEDEC). Field-Induced Charge-Device Model, applicable std. JESD22–C101–C. (ESD FICDM std. of JEDEC)
Continuous short circuit operation at elevated ambient temperature can result in exceeding the maximum allowed junction temperature
of 1500C.
The maximum power dissipation is a function of TJ(MAX) , θJA and TA. The maximum allowable power dissipation at any ambient
temperature is PD = (TJ(MAX) - TA)/θJA. All numbers apply for packages soldered directly onto a PC board.
OPERATING RATINGS (1)
Supply Voltage (VBAT - VSS)
Input Clock, SCLK_IN
2.5V to 5.5V
Frequency
Duty Cycle
Temperature Range
Board specification: 4LCELLPHONE
Package YFX
(2)
2
45% to 55%
-40°C to +85°C
Package Thermal Resistance θJA (2)
(1)
10 MHz to 52 MHz
153 °C/W
Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for
which the device is intended to be functional, but specific performance is not specified. For specifications and the test conditions, see
the Electrical Characteristics Tables.
The maximum power dissipation is a function of TJ(MAX) , θJA and TA. The maximum allowable power dissipation at any ambient
temperature is PD = (TJ(MAX) - TA)/θJA. All numbers apply for packages soldered directly onto a PC board.
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3.5 V ELECTRICAL CHARACTERISTICS (1)
Unless otherwise specified, all limits are specified at TJ = 25°C, VBAT = 3.5V, CBAT = 1µF, COUT = 2.2 µF (2), fSCLK_IN = 26 MHz,
IOUT = 1mA, Boldface limits apply at the temperature extremes.
Symbol
Parameter
Supply Current
IDD
Supply Current
CPD
Min (3)
Typ (4)
Max (3)
Units
Active Mode SCLK_IN = 19.2 MHz;
both clock outputs toggling; CLOAD
CLK1/2 = 0pF; IOUT = 0mA
1.4
1.65
1.7
mA
Active Mode SCLK_IN = 19.2 MHz;
both clock outputs toggling; CLOAD for
CLK1/2 = 33.5pF; IOUT = 0mA
3.7
4.45
4.50
mA
Active Mode SCLK_IN = 26 MHz, both
clock outputs toggling, CLOAD for
CLK1/2 = 0pF, IOUT=0mA
1.9
2.15
2.25
mA
Active Mode SCLK_IN = 26 MHz, both
clock outputs toggling, CLOAD for
CLK1/2 = 33.5 pF, IOUT=0mA
5
5.80
5.95
mA
In shutdown. Input clock not active.
CLK_REQ1/2=Low
0.1
1
µA
In shutdown. Input clock toggling.
CLK_REQ1/2=Low
0.1
1
uA
CLOAD for CLK1,2 = 0pF, Defined with
respect to VOUT = 1.8V
20
23.0
24.0
pF
Condition
(5) (6)
Power Dissipation Capacitance
per CLK output
Clock Outputs (CLK1/2) Figure 1, Figure 2
tPD_LH
Propagation Delay - Low to High
50% to 50%;
CLOAD = 33 pF; measured on CLK1
6.1
10.5
tPD_HL
Propagation Delay - High to Low
50% to 50%;
CLOAD = 33 pF; measured on CLK1
6.1
10.5
tSKEW
Skew Between Outputs (Either
Edge)
CLK1 to CLK2. 50% to 50%
1.5
3.1
tRISE
Rise Time (7)
For CL between 33.5 pF - 50 pF, 20% to
80%; typical value based on 40 pF load
2.1
3.7
5.9
tFALL
Fall Time (7)
For CL between 33.5 pF - 50 pF, 20% to
80%; typical value based on 40pF load
2
3.5
5
CLK_DC
Output Clock Duty Cycle
For CL between 33.5 pF - 50 pF
42
50
58
JitterRMS
Additive RMS period Jitter
fSCLK-IN= 26 MHz, BW =
100 Hz to 1MHz
(1)
(2)
(3)
(4)
(5)
(6)
(7)
ns
ns
CLK1
95
CLK2
110
%
fs
Electrical Table values apply only for factory testing (ATE) conditions at the temperature indicated. Factory testing conditions result in
very limited self-heating of the device such that TJ = TA. No specification of parametric performance is indicated in the electrical tables
under conditions of internal self-heating where TJ > TA.
CBAT, COUT: Low-ESR Surface-Mount Ceramic Capacitors (MLCCs) used in setting electrical characteristics.
Limits are 100% production tested at 25°C. Limits over temperature range are specified through correlations using statistical quality
control (SQC) method.
Typical values represent the most likely parametric norm as determined at the time of characterization. Actual typical values may vary
over time and will also depend on the application and configuration. The typical values are not tested and are not specified on shipped
production material.
Supply current depends on switching frequency and load.
Positive current is current flowing into the device.
This parameter is specified by design and/or characterization and is not tested in production.
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3.5 V ELECTRICAL CHARACTERISTICS(1) (continued)
Unless otherwise specified, all limits are specified at TJ = 25°C, VBAT = 3.5V, CBAT = 1µF, COUT = 2.2 µF(2), fSCLK_IN = 26 MHz,
IOUT = 1mA, Boldface limits apply at the temperature extremes.
Symbol
CLK1
Phase
Noise
Parameter
Additive Phase Noise
Additive Phase Noise
Typ (4)
All outputs enabled at 26 f = 100 Hz
MHz
f = 1 kHz
-128
f = 10 kHz
-150
f = 100 kHz
-160
f = 1 MHz
-163
f = 100 Hz
-127
f = 1 kHz
-146
f = 10 kHz
-153
f = 100 kHz
-161
f = 1 MHz
-163
All outputs enabled at 26 f = 100 Hz
MHz
f = 1 kHz
-127
f = 10 kHz
-148
f = 100 kHz
-160
f = 1 MHz
-162
f = 100 Hz
-129
f = 1 kHz
-144
f = 10 kHz
-151
f = 100 kHz
-163
f = 1 MHz
-164
All outputs enabled at
19.2 MHz
CLK2
Phase
Noise
Min (3)
Condition
All outputs enabled at
19.2 MHz
VOH
CLK1/2 Output Voltage High Level IOH = -2mA (equivalent output load
800Ω)
VOL
CLK1/2 Output Voltage Low Level
IOL = 2mA
ROFF
Ouput Impedance when disabled
with other output enabled (LDO
enabled)
Max (3)
Units
-144
dBc/Hz
-142
1.6
V
0.2
grounded
Both outputs disabled (LDO disabled)
diode to ground
System Clock Input (SCLK_IN)
VI-pp
SCLK_IN peak- to- peak input
level (7)
For duty cycle variation < 1%
IIH
Current into SCLK_IN pin (Input
HIGH)
SCLK_IN = 1.8V, CLK_REQ1/2=Low
IIL
Current into SCLK_IN pin (Input
LOW)
SCLK_IN = 0V, CLK_REQ1/2=Low
CIN
Input Capacitance (8)
CLK_REQ1/2=High
7.5
13
pF
RIN
Input Resistance (8)
CLK_REQ1/2=High
see Application Note: Input Impedance
14
20
kΩ
0.6
1
1.8
0
0.1
V
µA
–0.1
0
Switching Characteristics: System Clock Input
fSCLK_IN
System Clock
10
26
52
MHz
CLK_DC
Input Clock Duty Cycle
45
50
55
%
(8)
4
This parameter is specified by design and/or characterization and is not tested in production.
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3.5 V ELECTRICAL CHARACTERISTICS(1) (continued)
Unless otherwise specified, all limits are specified at TJ = 25°C, VBAT = 3.5V, CBAT = 1µF, COUT = 2.2 µF(2), fSCLK_IN = 26 MHz,
IOUT = 1mA, Boldface limits apply at the temperature extremes.
Symbol
Parameter
Condition
Min (3)
Typ (4)
12
6.2
Max (3)
Units
Clock Request Inputs (CLK_REQ1/2)
tSET
VIH
VIL
Setup Time from CLK_REQx to
SCLK_IN, to enable CLKx
(Figure 3)
CLK_REQ1/2 logic HIGH input
level. (clock output = ON) (9)
CLK_REQ1/2 logic LOW input
level. (clock output = OFF)
VBAT = 2.5V
1.4
VBAT = 3.5V
1.4
VBAT = 5.5V
1.4
ns
V
VBAT = 2.5V
0.4
VBAT = 3.5V
0.4
VBAT = 5.5V
0.4
IIH
Current into CLK_REQ pin
VIH = 1.8V, 200 kΩ pull down resistor
(Input HIGH)
IIL
Current into CLK_REQ pin
VIL = VSS, (Input LOW)
-0.2
0
Output Voltage
IOUT = 1mA
1.73
1.8
VOUT > 1.7V
0
8.5
V
14
µA
µA
LDO
VOUT
(10)
ILOAD
Load Current
VDO
Dropout Voltage (11)
ISC
Short Circuit Current Limit
PSRR
Power Supply Rejection Ratio
EN
TSHTDWN
ΔVOUT
Output Noise Voltage
IOUT = 10 mA Vout=1.7V
(12)
Thermal Shutdown
Line Transient
VBAT ripple = 200 mVPP,
IOUT = 10 mA
mA
92
90
f = 1 kHz
78
f = 10 kHz
60
f = 100 kHz
50
f = 1 MHz
50
f = 3.25 MHz
42
BW = 10 Hz to 100 kHz,
CLK_REQ1/2=High, Input clock not
active
18
Temperature
160
Hysteresis
20
TON
Turn on Time
µVRMS
°C
mV
1
-15
10
Overshoot on Startup
DC Output Resistance
dB
-1
IOUT = 10 mA to 0mA in 10 µs
ROUT
mA
mV
f = 217.5 Hz
IOUT = 0mA to 10 mA in 10 µs
10
300
VBAT = 3.4V to 2.8V in 30 µs, IOUT =
1mA
Load Transient
V
125
f = 100 Hz
VBAT = 2.8V to 3.4V in 30 µs, IOUT =
1mA
1.88
20
mV
mV
Ω
5
From rising edge of CLK_REQ1 to 95%
of VOUT(NOM)
200
260
350
µs
(9) Clock Request Inputs can tolerate logic high input levels up to VBAT.
(10) The device maintains stable, regulated output voltage without a load.
(11) Dropout voltage is the voltage difference between the input and the output at which the output voltage drops to 100 mV below its
nominal value.
(12) The noise figure is the noise of the LDO only; harmonics of the output clocks are excluded.
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TIMING DIAGRAMS
DC 50%
80%
80%
50%
50%
20%
20%
CLKx
tFALL
tRISE
Figure 1. Rise / Fall time and Duty Cycle Waveform for Clock Outputs
50%
50%
SCLK_IN
tpdLH
tpdHL
50%
50%
CLK1
Skew
Skew
50%
50%
CLK2
Figure 2. Clock Output Timing Waveforms
50%
CLK_REQ1
50%
50%
CLK_REQ2
tSET
tSET
SCLK_IN
50%
Figure 3. Clock Request Timing Waveforms
6
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Connection Diagram
Top View
2
CLK1
CLK_
REQ1
CLK_
REQ2
CLK2
1
VBAT
VOut
SCLK_IN
VSS
A
B
C
D
Figure 4. 8-Bump DSBGA
See YFX0008 Package
PIN DESCRIPTIONS
(1)
Port /
Direction
Type
(1)
Pin
Pin Name
Description
C1
SCLK_IN
Host
Input
A2
CLK1
Peripheral
Output
B2
CLK_REQ1
Peripheral
Input
D2
CLK2
Peripheral
Output
C2
CLK_REQ2
Peripheral
Input
A1
VBAT
Battery /
Input
Power
Power Supply
B1
Vout
LDO /
Output
Power
Power Supply to Clock Source and clock outputs
D1
VSS
Ground
Ground
Ground Pin
Source Clock Input
Clock Output 1
Clock Request Input 1 Clock1 = ON at high level
Clock Output 2
Clock Request Input 2 Clock2 = ON at high level
I = Input, O = Output, I/O = Input / Output
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TYPICAL PERFORMANCE CHARACTERISTICS
Unless otherwise specified, TA = 25°C, VBAT = 3.5V, fSCLK_IN = 26 MHz, COUT = 2.2 µF
Supply Current
vs.
Supply Voltage
Supply Current
vs.
Input Clock Frequency
6.0
12.0
SCLK-IN = 26 MHz
CLOAD = 33 pF
11.0
5.4
5.2
25°C
5.0
4.8
4.6
50pF
10.0
5.6
SUPPLY CURRENT (mA)
SUPPLY CURRENT (mA)
5.8
-40°C
85°C
4.4
33pF
9.0
8.0
7.0
6.0
5.0
4.0
3.0
2.0
4.2
1.0
4.0
2.5
0.0
0
3.0
3.5
4.0
4.5
5.0
5.5
10 pF 0 pF
22 pF
10
SUPPLY VOLTAGE (V)
20
30
40
50
CLOCK FREQUENCY (MHz)
Figure 5.
Figure 6.
Supply Current
vs.
Capacitive Load
LDO output Voltage
vs.
Supply Voltage
7.0
1.82
ILOAD = 1 mA
26 MHz/CLK1+2
1.81
5.0
19 MHz/CLK1+2
VOUT (V)
SUPPLY CURRENT (mA)
6.0
4.0
3.0
2.0
1.79
1.0
19 MHz/CLK1
26 MHz/CLK1
0.0
0
25°C
1.80
10
20
30
40
-40°C
85°C
1.78
2.5
50
3.0
CAPACITIVE LOAD (pF)
3.5
4.0
4.5
5.0
5.5
SUPPLY VOLTAGE (V)
Figure 7.
Figure 8.
LDO output Voltage
vs.
LDO output current
LDO output voltage ON timing
2.0
1.85
1.6
1.80
1.75
LDO VOLTAGE (V)
LDO OUTPUT VOLTAGE (V)
1.8
-40°C
85°C
25°C
1.70
CLK REQ
LDO OUTPUT
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
1.65
0
2
4
6
8
10
0
100
200
300
400
TIME (Ps)
LOAD CURRENT (mA)
Figure 9.
8
-0.2
-100
Figure 10.
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TYPICAL PERFORMANCE CHARACTERISTICS (continued)
Unless otherwise specified, TA = 25°C, VBAT = 3.5V, fSCLK_IN = 26 MHz, COUT = 2.2 µF
Additive Phase Noise
vs.
Frequency Offset
LDO output voltage OFF timing
-110
2.0
1.8
-120
PHASE NOISE (dBc/Hz)
LDO VOLTAGE (V)
1.6
LDO 1 mA
1.4
1.2
LDO 10 mA
1.0
0.8
0.6
0.4
0.2
-130
CLK2_26 MHz
-140
CLK1 - 26 MHz
-150
CLK1 - 19 MHz
-160
CLK2_19 MHz
0.0
-0.2
-2k
CLK REQ
0
2k
4k
6k
8k
-170
100
10k
TIME (Ps)
10k
100k
1M
FREQUENCY OFFSET (Hz)
Figure 11.
Figure 12.
CLK1 Pulse Response 10-50pF @ 19MHz
Power Supply Rejection Ratio
vs.
Frequency
1.8
100
90
1.3
CL = 10 pF
80
CL = 22 pF
0.9
PSRR (dB)
CLK1 (V)
1k
CL = 33 pF
CL = 50 pF
0.4
70
60
0.0
50
CLK1 OUTPUT @ 19 MHz
-0.5
-60
-50
-40
-30
-20
-10
40
100
0
TIME (ns)
1k
10k
100k
1M
10M
POWER SUPPLY REJECTION RATIO
Figure 13.
Figure 14.
CLK1 Pulse Response 10-50pF @ 26MHz
CLK1 Pulse Response 10-50pF @ 52MHz
1.8
1.8
1.3
1.3
CL = 10 pF
0.9
CLK1 (V)
CLK1 (V)
COUT: 2.2 PF
VBAT: No Capacitors
CL = 22 pF
CL = 33 pF
0.4
0.9
CL = 22 pF
0.4
CL = 50 pF
CL = 33 pF
CL = 50 pF
0.0
0.0
CLK1 OUTPUT @ 26 MHz
-0.5
-10
CL = 10 pF
0
10
20
30
40
CLK1 OUTPUT @ 52 MHz
50
TIME (ns)
-0.5
15
25
35
TIME (ns)
Figure 15.
Figure 16.
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APPLICATION INFORMATION
The LMH2191 is a complete 52 MHz clocking conditioner and clock tree driver. The LMH2191 is used to supply
a common clock to mobile phone peripherals such as Bluetooth, Wireless LAN, and/or Digital Video Broadcast-H
(DVB-H). The high isolation between the clock outputs ensures that the peripherals don't disrupt each other. Its
excellent phase noise characteristics prevent the clock quality from deteriorating. A typical LMH2191 setup is
depicted in Figure 17.
VBAT
VBAT
CBAT
1 µF
A1
VOUT
LMH2191
B1
1.8V LDO
COUT
VDD
CCLK
10 nF
A2
2.2 µF
SCLK_IN
Clock
Source
C1
CSERIES
Clock
Tree
Driver
CLK1
Peripheral
D2
CLK2
Peripheral
B2
Clock
Request
CLK_REQ1
C2 CLK_REQ2
D1
VSS
Figure 17. LMH2191 Typical Application Schematic
The internal structure of the LMH2191 is depicted in the block diagram of Figure 18.
10
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VBAT
A1
VOUT
LMH2191
B1
1.8V LDO
On/Off
VOUT
Clock Tree Driver
SCLK_IN
A2 CLK1
C1
D2 CLK2
CSERIES
VBAT
B2
CLK_REQ1
C2
CLK_REQ2
Clock Request Logic
D1
VSS
Figure 18. Block Diagram
The LMH2191 clock distribution circuit is comprised of 3 blocks:
• Clock tree driver
• Clock request logic
• Low Dropout Regulator (LDO)
The clock tree driver provides a clean clock to 2 separately connected peripheral devices. Independent clock
request inputs allow the peripheral to control when the particular clock should be enabled. Furthermore, both
clock request inputs control the LDO output voltage, e.g., when both request inputs are low (no CLK1 and no
CLK2 output required), the LDO voltage is disabled. The LDO provides a low-noise, high-PSRR supply voltage
that enables low phase noise on the clock outputs, and low quiescent current for portable applications. It can
also be used to supply the TCXO. The following sections provide a detailed description of each block.
CLOCK TREE DRIVER
The clock tree driver consists of one input that drives 2 outputs. It is supplied by a high-precision voltage
regulator of 1.8V, the LDO. The Clock outputs are enabled when the appropriate Clock Request inputs are logic
high.
Clock Tree Driver Input
The source clock input (SCLK_IN) is the input for the clock tree driver. This input has an internally connected
coupling capacitor (CSERIES) with a value of 33pF. In shutdown mode (when both CLK_REQ inputs are low), the
input stage is completely switched off to prevent unnecessary power consumption when the source clock is still
present.
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Due to the internal coupling capacitor, the clock signal is DC biased, since the coupling capacitor prevents the
internal biasing of the input circuitry to be affected by the external DC voltage. Because of the coupling capacitor,
the minimum clock frequency is 10 MHz. It is assumed that the input signal is a sine wave or a typical TCXO
waveform (the signal from a TCXO has slow edges), enabling the control loop to adjust to a duty cycle of 50% if
the input signal differs slightly from 50% duty cycle. The duty cycle is an important timing parameter for the
peripheral equipment. The circuit that adjust the duty cycle is shown in Figure 19.
SCLK_IN
CSERIES
Figure 19. Clock Duty Cycle Regulation
Duty Cycle 50%
Shifted DC level
DC level 50% duty cycle
Duty Cycle 50%
Figure 20. Duty Cycle adjust levels
|n order to achieve a duty cycle of 50%, the edges of the incoming clock signal (SCLK_IN) are used to move the
switching point to the level that is needed to create the 50% duty cycle. The simplified input circuit consists of an
inverter and a feedback resistor. Together with the input series capacitor of about 30 pF, the circuit creates a DC
level depending on the duty cycle of the incoming clock signal. When the duty cycle is exactly 50%, the DC level
is in the middle of the upper and lower pulse level. When the duty cycle differs from 50%, the DC level shifts
slightly to maintain the duty cycle level at 50%. (See Duty Cycle adjust levels of Figure 20.) As explained above,
the slow edges of the SCLK_IN signal are important to make the control loop work.
Input Impedance
The input impedance can be split up into two parts: the DC input resistance and the AC input impedance. Due to
the used series capacitor in the input signal path the DC resistance is infinite. The AC input impedance is formed
by the circuit drawn in Figure 19. This circuit consists of an inverter and a feedback resistor. A signal fed to the
input pin is connected to the inverter input which has a high input impedance and is in parallel to the feedback
resistor of 30 kΩ. The other pin of the feedback resistor is connected to the output of the inverter which means
that the input current is higher than it would be if it were connected to a decoupled supply connection. For this
reason the AC input resistance can be much lower than the connected feedback resistor of 30 kΩ. The input
resistance is dependant on the amplitude of the input signal. When an input amplitude of 1.8V is used (the same
amplitude as the output of the inverter), the input impedance is theoretical half the value of the feedback resistor.
When the amplitude of the input signal lowers, the input resistance becomes lower too. With an input signal of
1VPP, the input impedance will be about 10 kΩ.
Clock Tree Driver Outputs
The LMH2191's clock tree driver outputs have a drive strength that make each output capable of driving a
capacitive load up to 50 pF, together with a minimum of EMI. Further reduction of EMI is achieved by the
inversion of the CLK2 output. (See Figure 21.) Both the drive strength and the capacitive load make the edges of
the output pulse relative slow which is favorable for EMI reduction.
12
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SCLK_IN
CLK 1
CLK 2
Figure 21. Clock Outputs
CLOCK REQUEST LOGIC
A clock request input is provided for each clock output. This allows the peripheral device to control when it wants
to receive a clock. In case the application does not have clock request functionality, the CLKx_REQ can be hard
wired to a logic high level to enable the clock output continuously. The clock request inputs have logic levels
compatible with 1.8V logic, but can tolerate logic high levels up to VBAT.
CLK_REQ x
D Q
CLK signal
Inverter only
added for CLK2
CLKx
Figure 22. Enabling the output
The clock request logic enables an independent control of the clock tree driver outputs, CLK1 and CLK2, as well
as an LDO disable when both request inputs are low.
The on and off switching of the clock output drivers is done synchronously with the clock input in order to prevent
glitches at the clock output. For this the clock request signal is connected to the D input of a latch. The Q output
of this latch enables the clock output driver (see Figure 22). For the CLK1 output the CLK input signal is
connected via an inverter to the clock input of the latch. In this way the latch enables and disables the CLK1
output buffer on the falling edge of the clock signal. For the CLK2 output an extra inverter is inserted prior to the
latch circuit, and the CLK2 output buffer is enabled and disabled on the rising edge of the clock input signal
(equal to the falling edge of the CLK2 output signal).
LOW DROPOUT REGULATOR
The linear and Low-Dropout regulator (LDO) is used to regulate the input voltage, VBAT, thus generating a welldefined ultra low noise 1.8V supply voltage. This allows the LMH2191 to suppress VBAT supply voltage ripple and
noise for the TCXO and the internal Clock Path. Voltage ripple and noise would distort clock edges causing extra
phase noise on the distributed clock signal.
The LDO is powered up whenever a Clock Request is active; it supports overheating detection and will switch off
in case overheating occurs. The recommended sequence for powering up the LDO is to raise a clock request to
a high level with the supply already powered up. Thus the LDO stays in shutdown mode with sub µA current
consumption until an output clock is actually needed. The LDO will power up within the turn-on time of about 200
µs (as specified in the data sheet tables). Alternatively, the clock request input can be hard wired to VBAT which
powers up the LDO simultaneously with VBAT. A drawback is that the LDO and clock path (and if connected, the
TCXO) will always draw current when VBAT is powered up. Also, in this setup, care should be taken with supplies
with an excessive long startup time of more than about 25 ms. Under this condition the LDO could exhibit
excessive long turn-on delay (order of seconds.)
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LMH2191
SNAS485D – JULY 2010 – REVISED MAY 2013
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LAYOUT RECOMMENDATIONS
As with any other device, careful attention must be paid to the board layout. If the board isn't properly designed,
the performance of the device can be less than desired. Care should be taken that the SCLK_IN input trace and
the output traces of CLK1 and CLK2 are as short as possible to reduce extra capacitive load observed by the
clock outputs. Also proper de-coupling close to the device is necessary. Table 1 depicts the advised component
values. TI suggests to use the evaluation board, available from the Texas Instruments web site www.ti.com, as a
guide for layout and as an aid in device testing and characterization.
Table 1. Recommended Component Values
Symbol
Parameter
Min
Typ
CBAT (1)
Capacitor on VBAT
0.47
1
COUT (1)
Capacitor on VOUT
1
2.2
ESR
Equivalent Series Resistance
5
(1)
14
Max
Units
µF
500
mΩ
CBAT, COUT: Low-ESR Surface-Mount Ceramic Capacitors (MLCC's) used in setting electrical characteristics.
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SNAS485D – JULY 2010 – REVISED MAY 2013
REVISION HISTORY
Changes from Revision C (April 2013) to Revision D
•
Page
Changed layout of National Data Sheet to TI format .......................................................................................................... 14
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PACKAGE OPTION ADDENDUM
www.ti.com
10-Dec-2020
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
(2)
Lead finish/
Ball material
MSL Peak Temp
Op Temp (°C)
Device Marking
(3)
(4/5)
(6)
LMH2191TME/NOPB
ACTIVE
DSBGA
YFX
8
250
RoHS & Green
SNAGCU
Level-1-260C-UNLIM
-40 to 85
5
LMH2191TMX/NOPB
ACTIVE
DSBGA
YFX
8
3000
RoHS & Green
SNAGCU
Level-1-260C-UNLIM
-40 to 85
5
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of
