TDA9109SN View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'TDA9109SN' PDF : 30 Pages View PDF
TDA9109/SN
OPERATING DESCRIPTION (continued)
IV - DC/DC CONVERTER PART
This unit controls the switch-mode DC/DC con-
verter. It converts a DC constant voltage into the
B+ voltage (roughly proportional to the horizontal
frequency) necessary for the horizontal scanning.
ThisDC/DC converter must be configured in step-
up mode. It operates very similarly to the well
known UC3842.
IV.1 - Step-up Mode
Operating Description
- The power MOS is switched-on at the middle of
the horizontal flyback.
- The power MOS is switched-off when its current
reachesa predeterminedvalue. For this purpose,
a sense resistor is inserted in its source. The
voltage on this resistor is sent to Pin16 (ISENSE).
- The feedback (coming either from the EHV or
from the flyback) is divided to a voltage close to
Figure 17 : DC/DC Converter
I2C
4.8V and compared to the internal4.8V reference
(IVREF). The difference is amplified by an error
amplifier, the output of which controls the power
MOS switch-off current.
Main Features
- Switching synchronized on the horizontal fre-
quency,
- B+ voltage always higher than the DC source,
- Current limited on a pulse-by-pulse basis.
The DC/DC converter is disabled :
- when VCC or VDD are too low,
- when X-Ray protection is latched,
- directly through I2C bus.
When disabled, BOUT is driven to GND by a 0.5mA
current source. This feature allows to implement
externally a soft start circuit.
DAC
7bits
8V
± Iadjust
4.8V ±20%
95dB
A
Inhibit
SMPS Soft
Start
Σ
1/3
C2
1.2V
1.2V
C3
REGIN
15
COMP
14
ISENSE
16
1MΩ
22kΩ
L
+
400ns
12V
S
Q
R
BOUT
28
Inhibit SMPS
TDA9109/SN
VB+
24/30
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