cx25840 Conexant Systems, Inc., cx25840 Datasheet - Page 140

• Manufacturer Part Number: cx25840
• Description: Video Decoder And Broadcast Audio
• Manufacturer: Conexant Systems, Inc.

Electrical Interfaces
Figure 4-3. Single-Ended Clock Input
4.4.1
4-4
On-Chip Regulator
XTAL Oscillator
A linear voltage regulator is integrated on-chip in order to provide a means to convert
the 3.3 V external power supply to a 1.2 V supply to be used for powering the core
logic. This relieves the system of having to provide a separate 1.2 V supply for the
decoder. The regulator is designed to only accommodate the power needs of the chip.
This supply cannot be used for any other components on the board.
The regulator controls the base (or gate) of an external pass transistor such that the
emitter (source/drain) is driven to 1.2 V. Specifications are listed in
The regulator requires two external pins, REG_IN and REG_OUT, to be connected.
The REG_OUT pin provides the base current for the external NPN. The REG_IN pin
provides the feedback voltage from the emitter terminal of the external pass transistor.
Figure 4-4
regulator.
Additionally, the regulator can be bypassed and a system voltage of 1.2 V applied
directly to the VDD pins if so desired. In this case, the REG_OUT pin must be tied to
REG_IN.
The advantage to using the on-chip regulator is that a localized regulator can be
carefully monitored and controlled with registers. Advantages to not using the on-chip
regulator are that a better heat dissipation is achieved on the board, and a lower bill of
material results, assuming that another device is supplying the 1.2 V supply.
Table 4-2. Voltage Regulator Specifications
Supply Range
Regulated Voltage
Regulated Voltage Tolerance
Current Output Range
1.5 nF
illustrates the external components required for using the on-chip
Parameter
AGND
10 kΩ
10 nF
Conexant
AGND
3.3 V
VAA
3.0–3.6
1.2–1.38
±100
0–250
Requirement
1 kΩ
1 kΩ
V
V
mV
mA
XTO
Units
XTI
CX2584X
CX25840/1/2/3 Data Sheet
Table
4-2.
102284_024b
102284B
8/3/05