TEA1654T NXP Semiconductors, TEA1654T Datasheet - Page 6

• Manufacturer Part Number: TEA1654T
• Manufacturer: NXP Semiconductors

Specifications of TEA1654T

• Operating Temperature (max): 145C
• Operating Temperature (min): -20C
• Pin Count: 14
• Mounting: Surface Mount
• Package Type: SO
• Screening Level: Commercial
• Lead Free Status / Rohs Status: Compliant

Philips Semiconductors
Current mode control
Current mode control is used for its good line regulation
behaviour.
The ‘on-time’ is controlled by the internally inverted control
pin voltage, which is compared with the primary current
information. The primary current is sensed across an
external resistor. The driver output is latched in the logic,
preventing multiple switch-on.
The internal control voltage is inversely proportional to the
external control pin voltage, with an offset of 1.5 V. This
means that a voltage range from 1 to 1.5 V on pin CTRL
will result in an internal control voltage range from
0.5 to 0 V (a high external control voltage results in a low
duty cycle).
Oscillator
2003 May 12
handbook, halfpage
handbook, halfpage
GreenChip II SMPS control IC
Fig.5 V
V sense(max)
(kHz)
0.52 V
f
65
24
Fig.4 Multi mode operation.
VCO
sense(max)
(typ)
1 V
fixed
as a function of V
quasi resonant
1.5 V
(typ)
CTRL
V CTRL
MDB217
MGU233
P (W)
.
6
The maximum fixed frequency of the oscillator is set by an
internal current source and capacitor. The maximum
frequency is reduced once the control voltage enters the
VCO control window. Then, the maximum frequency
changes linearly with the control voltage until the minimum
frequency is reached (see Figs 5 and 6).
VCO adjustment
The VCOadj pin can be used to set the VCO operation
point. As soon as the peak voltage on the sense resistor is
controlled below half the voltage on the VCOadj pin (VCO
level), frequency reduction will start. The actual peak
voltage on sense will be somewhat higher due to switch-off
delay (see Fig.7). The frequency reduction will stop
approximately 25 mV lower (VCO
minimum frequency is reached.
Cycle skipping
At very low power levels, a cycle skipping mode will be
activated. A high control voltage will reduce the switching
frequency to a minimum of 24 kHz. If the voltage on the
control pin has raised even more, switch-on of the external
power MOSFET will be inhibited until the voltage on the
control pin has dropped to a lower value again (see Fig.7).
For system accuracy, it is not the absolute voltage on the
control pin that will trigger the cycle skipping mode, but a
signal derived from the internal VCO will be used.
Remark: If the no-load requirement of the system is such
that the output voltage can be regulated to its intended
level at a switching frequency of 24 kHz or above, the
cycle skipping mode will not be activated.
handbook, halfpage
Fig.6 VCO frequency as a function of V
(kHz)
f
65
24
VCO 2
level
VCO 1
level
2
level), when the
V sense(max) (V)
Product specification
TEA1654
MCE407
sense(max)
.
1