AN1657 datasheet(6/9 Pages) STMICROELECTRONICS

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AN1657 APPLICATION NOTE

6/9

Under steady-state operation the L6565 will be then shortly activated with a repetition rate TRep essentially

given by TDecay + TRestart, where TDecay is the time that VCC takes to span VCC hysteresis downward:

and Iq is the quiescent consumption of the L6565. The input of the linear regulator is a sawtooth going

from a peak

≈VT to a valley that depends on TRep, C13 and the input current to the LE50CZ. Also Vcc is

a sawtooth going up and down from VCCOn to VCCOff .

When the monitor is to resume its normal operation the OFF input will be grounded thus inhibiting Q4 and

disabling the OFF-mode circuit. However, the L6565 will be able to respond only when it is active. Under

the worst-case conditions, that is the OFF input is grounded just after the IC has been shut down, the

L6565 will be responsive only after a time TRep. The power management software must take this into ac-

count, re-enabling the loads on all of the outputs with a delay not shorter than TRep after grounding the

OFF input.

Experimental results

In the following tables the results of some bench evaluations are summarized. Some waveforms at full

load and off-mode under different line conditions are shown for user's reference, with some stress on the

OFF-mode management of the "1W initiative" compliant design.

As to the full-load performance there is no significant difference between the two designs presented: table

3 is common to both. Same applies to table 4 that shows the consumption during Suspend-mode opera-

tion, a particular low-consumption mode envisaged by VESA standards. No special action is taken to keep

the consumption below the limit (Pin < 15W): the converter can comfortably fulfill this requirement.

Table 3. L6565-based, 90W SMPS for CRT monitor: line regulation and full load efficiency

Table 4. L6565-based, 90W SMPS for CRT monitor: Suspend-mode consumption

VAC [V]

110

132

176

220

264

Pin [W]

103.9

101.0

99.6

98.4

98.6

Vout [V]

199.90

199.87

199.84

199.83

199.86

199.82

79.45

79.40

79.39

79.37

79.38

79.39

14.12

14.13

14,14

14.14

14.16

-14.20

-14.21

-14.22

6.58

6.60

6.62

6.63

6.64

6.65

Pout [W]

90.59

90.61

90.63

90.64

90.69

η [%]

87.2

89.7

91.0

92.1

92.2

92.0

Load conditions: 200V: 0.33A; 80V: 0.13A;

±15V: 80 Ω; 6.5V: 10Ω; 5V: 0.05A

VAC [V]

110

132

176

220

264

Pin [W]

12.6

12.9

13.3

13.4

13.6

Load conditions: 200V: 0.005A, 80V: 0.065A;

±15V = open; 6.5V: 10Ω (heater on); 5V: 0.025A. Pout ≈ 9.3W

Pin [W]

8.3

8.5

8.6

8.7

Load conditions: 200V: 0.005A, 80V: 0.065A;

±15V = 6.5V = open (heater off); 5V: 0.025A (LDO regulator supplied

from 6.5V line). Pout

≈ 6.3W.

Note: a) Applicable to EnergyStar® compliant design only.

b) Efficiency improvement is due to onset of L6565 burst-mode operation.

Dec ay

-------- V

CCHy s

≈

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