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參數(shù)資料
| 型號： | LMX2335UTM/NOPB |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | PLL合成/DDS/VCOs |
| 英文描述： | PLL FREQUENCY SYNTHESIZER, 1200 MHz, PDSO16 |
| 封裝： | PLASTIC, TSSOP-16 |
| 文件頁數(shù)： | 29/48頁 |
| 文件大?。?/td> | 3127K |
| 代理商： | LMX2335UTM/NOPB |
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1.0 Functional Description (Continued)
1.8.2 Open Drain FastLock Output
The LMX233xU Fastlock feature allows faster loop response
time during lock aquisition. The loop response time (lock
time) can be approximately halved if the loop bandwidth is
doubled. In order to achieve this, the same gain/ phase
relationship at twice the loop bandwidth must be maintained.
This can be achieved by increasing the charge pump current
from 0.95 mA (ID
o RF1 Bit = 0) in the steady state mode, to
3.8 mA (ID
o RF1 Bit = 1) in Fastlock. When the FoLD output
is configured as a FastLock output, an open drain device is
enabled. The open drain device switches in a parallel resis-
tor R2’ to ground, of equal value to resistor R2 of the external
loop filter. The loop bandwidth is effectively doubled and
stability is maintained. Once locked to the correct frequency,
the PLL will return to a steady state condition. Refer to
Section 2.8 F
oLD for details on how to configure the FoLD
output to an open drain Fastlock output.
1.8.3 Counter Reset
Three separate counter reset functions are provided. When
the F
oLD is programmed to Reset RF2 Counters, both the
RF2 feedback divider and the RF2 reference divider are held
at their load point. When the Reset RF1 Counters is pro-
grammed, both the RF1 feedback divider and the RF1 ref-
erence divider are held at their load point. When the Reset
All Counters mode is enabled, all feedback dividers and
reference dividers are held at their load point. When the
device is programmed to normal operation, both the feed-
back divider and reference divider are enabled and resume
counting in ‘close’ alignment to each other. Refer to Section
2.8 F
oLD for more details.
1.8.4 Reference Divider and Feedback Divider Output
The outputs of the various N and R dividers can be moni-
tored by selecting the appropriate F
oLD word. This is essen-
tial when performing OSC
in or fIN sensitivity measurements.
Refer to the Test Setups section for more details. Refer to
Section 2.8 F
oLD for more details on how to route the
appropriate divider output to the F
oLD pin.
1.9 POWER CONTROL
Each synthesizer in the LMX2335U or LMX2336U is indi-
vidually power controlled by device powerdown bits. The
powerdown word is comprised of the PWDN RF1 (PWDN
RF2) bit, in conjuction with the TRI-STATE ID
o
RF1
(TRI-STATE ID
o RF2) bit. The powerdown control word is
used to set the operating mode of the device. Refer to
Sections 2.4.4, 2.5.4, 2.6.4, and 2.7.4 for details on how to
program the RF1 or RF2 powerdown bits.
When either the RF1 synthesizer or the RF2 synthesizer
enters the powerdown mode, the respective prescaler,
phase detector, and charge pump circuit are disabled. The
D
o RF1 (Do RF2), fIN RF1 (fIN RF2), and fIN RF1 (fIN RF2)
pins are all forced to a high impedance state. The reference
divider and feedback divider circuits are held at the load
point during powerdown. The oscillator buffer is disabled
when both the RF1 and RF2 synthesizers are powered
down. The OSC
in pin is forced to a HIGH state through an
approximate 100 k
resistance when this condition exists.
When either synthesizer is activated, the respective pres-
caler, phase detector, charge pump circuit, and the oscillator
buffer are all powered up. The feedback divider, and the
reference divider are held at load point. This allows the
reference oscillator, feedback divider, reference divider and
prescaler circuitry to reach proper bias levels. After a finite
delay, the feedback and reference dividers are enabled and
they resume counting in ‘close’ alignment (the maximum
error is one prescaler cycle). The MICROWIRE control reg-
ister remains active and capable of loading and latching data
while in the powerdown mode.
Synchronous Powerdown Mode
In this mode, the powerdown function is gated by the charge
pump. When the device is configured for synchronous pow-
erdown, the device will enter the powerdown mode upon
completion of the next charge pump pulse event.
Asynchronous Powerdown Mode
In this mode, the powerdown function is NOT gated by the
completion of a charge pump pulse event. When the device
is configured for asynchronous powerdown, the part will go
into powerdown mode immediately.
TRI-STATE ID
o
PWDN
Operating Mode
0
PLL Active, Normal Operation
1
0
PLL Active, Charge Pump Output in High Impedance State
0
1
Synchronous Powerdown
1
Asynchronous Powerdown
Notes:
1. TRI-STATE ID
o refers to either the TRI-STATE IDo RF1 or TRI-STATE IDo RF2 bit .
2. PWDN refers to either the PWDN RF1 or PWDN RF2 bit.
LMX2335U/LMX2336U
www.national.com
35
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