SSL4101T

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© NXP B.V. 2011. All rights reserved.

Product data sheet

Rev. 1 — 21 April 2011

13 of 29

NXP Semiconductors

SSL4101T

GreenChip III+ SMPS control IC

capacitance on the drain node.

As soon as the internal oscillator voltage is high again and the secondary stroke has

ended, the circuit waits for the lowest drain voltage before starting a new primary stroke.

Figure 8 shows the drain voltage, valley signal, secondary stroke signal and the internal

oscillator signal.

Valley switching allows high frequency operation as capacitive switching losses are

reduced, see Equation 2. High frequency operation makes small and cost-effective

magnetics possible.

(2)

7.3.3 Current mode control (FBSENSE pin)

Current mode control is used for the flyback converter for its good line regulation.

The primary current is sensed by the FBSENSE pin across an external resistor and

compared with an internal control voltage. The internal control voltage is proportional to

the FBCTRL pin voltage, see Figure 9.

(1) Start of new cycle at lowest drain voltage.

(2) Start of new cycle in a classical Pulse Width Modulation (PWM) system without valley detection.

Fig 8.

Signals for valley switching

P

1

2

---

C

d

V

2

×

f

×

×

=

⎝⎠

⎛⎞

drain

secondary

stroke

014aaa027

secondary

ringing

primary

stroke

valley

(2)

(1)

secondary

stroke

oscillator