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PDF TEA1755T Data sheet ( Hoja de datos )
| Número de pieza | TEA1755T | |
| Descripción | HV start-up DCM/QR flyback controller | |
| Fabricantes | NXP Semiconductors | |
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TEA1755T
HV start-up DCM/QR flyback controller with integrated
DCM/QR PFC controller
Rev. 1.1 — 13 March 2015
Product data sheet
1. General description
The GreenChip is the latest generation of green Switched Mode Power Supply (SMPS)
controller ICs. The TEA1755T combines a controller for Power Factor Correction (PFC)
and a flyback controller. Its high level of integration enables cost-effective power supply
design using a very low number of external components.
The PFC operates in Quasi-Resonant (QR) or Discontinuous Conduction Mode (DCM),
with valley switching.
The specially built-in green functions provide high efficiency at all power levels. At high
power levels the flyback operates in QR mode or DCM with valley detection. At medium
power levels, the flyback controller switches to Frequency Reduction (FR) mode and limits
the peak current to an adjustable minimum value. In low power mode, the PFC switches
off to maintain high efficiency. At very low power levels, when the flyback switching
frequency drops below 25 kHz, the flyback converter switches to burst mode. During the
non-switching phase of burst mode, the internal IC supply current is minimized to further
optimize efficiency. Valley switching is used in all operating modes.
The advanced burst mode ensures high-efficiency at low power and good standby power
performance while minimizing audible transformer noise.
The TEA1755T is a Multi-Chip Module, (MCM), containing two chips. The proprietary
high-voltage BCD800 process makes direct start-up possible from the rectified universal
mains voltage in an effective and green way. The second low voltage Silicon-On-Insulator
(SOI) is used for accurate, high-speed protection functions and control.
The TEA1755T enables easy design of highly efficient and reliable supplies up to 250 W.
These power supply designs are cost-effective, requiring the minimum number of external
components.
Remark: All values in this document are typical values unless otherwise stated.
1 page  
NXP Semiconductors
TEA1755T
HV start-up DCM/QR flyback controller with integrated DCM/QR PFC
controller
7. Functional description
7.1 General control
The TEA1755T contains a power factor correction circuit controller and a flyback circuit
controller. A typical configuration is shown in Figure 3.
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(1) The HV pin can either be connected to the center tap of the flyback transformer or to the drain of MOSFET S2.
Fig 3. A typical TEA1755T configuration
7.1.1 Start-up and UnderVoltage LockOut (UVLO)
Initially, the capacitor on the VCC pin is charged from the high-voltage mains using the HV
pin.
When VCC is less than Vtrip, the charge current is Ich(low). This low current protects the IC if
the VCC pin is shorted to ground. To ensure a short start-up time, the charge current above
the Vtrip level is increased to Ich(high), until VCC reaches Vth(UVLO). When VCC is between
Vth(UVLO) and Vstartup, the charge current goes low again to ensure a low safe restart duty
cycle during fault conditions.
The control logic activates the internal circuitry and switches off the HV charge current
when VCC passes the Vstartup level. First, the LATCH pin current source is activated and
the soft-start capacitors on the PFCSENSE and FBSENSE pins are charged. Also the
clamp circuit on the PFCCOMP pin is activated.
The PFC circuit is activated when the following conditions are met:
TEA1755T
Product data sheet
All information provided in this document is subject to legal disclaimers.
Rev. 1.1 — 13 March 2015
© NXP Semiconductors N.V. 2015. All rights reserved.
5 of 35
5 Page 
NXP Semiconductors
TEA1755T
HV start-up DCM/QR flyback controller with integrated DCM/QR PFC
controller
A switch discharges the PFCTIMER pin capacitor when the flyback controller operating
frequency is > fsw(fb)swon(PFC) (73 kHz). At the same moment, the PFC stage is also
switched on.
Connect a capacitor to the PFCTIMER pin (see Section 7.2.7) to prevent the PFC from
switching off due to a dynamic load that leads to repetitive crossing of fsw(fb)swoff(PFC) and
fsw(fb)swon(PFC). A 1 nF minimum capacitor value is recommended to prevent noise
influencing the PFC switch on/ switch off behavior.
The PFCTIMER pin capacitor is also discharged when the flyback maximum switching
frequency is higher than 53 kHz. This feature prevents PFC on/off toggling during
dynamic loads causing the flyback to operate repetitively near fsw(fb)swoff(PFC) and
fsw(fb)swon(PFC).
It is also possible to control PFC switch-on and switch off externally. When VPFCTIMER is
driven below 1.03 V, the PFC stage is on. When the PFCTIMER pin voltage is driven
above 4.4 V, the PFC stage is switched off. The external control overrides the PFC stage
control by the flyback controller (see Figure 6).
The PFCTIMER pin has an internal clamp circuit starting around 10 V with a current
capability of 0.1 mA
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Fig 6. PFC switch on and switch off using the PFCTIMER pin
7.2.8 Dual-boost PFC
The mains input voltage modulates the PFC output voltage. The mains input voltage is
measured using the VINSENSE pin. If VVINSENSE < 2.28 V, the current is sourced from the
VOSENSE pin. To ensure switch-over is stable, the current reaches its absolute maximum
value for VVINSENSE < 2.08 V, see Figure 7.
At low VINSENSE input voltages, the output current is 8.1 A. This output current, in
combination with the resistors on the VOSENSE pin, sets the lower PFC output voltage
level at low mains voltages. At high mains input voltages, the current is switched to zero.
The PFC output voltage is then at its maximum. As this current is zero in this situation, it
does not affect the accuracy of the PFC output voltage.
To ensure a correct switch-off of the application, the VOSENSE current switches to its
maximum value of 8.1 A when VVOSENSE drops below 2.1 V.
TEA1755T
Product data sheet
All information provided in this document is subject to legal disclaimers.
Rev. 1.1 — 13 March 2015
© NXP Semiconductors N.V. 2015. All rights reserved.
11 of 35
11 Page | ||
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