L6599ATD STMicroelectronics, L6599ATD Datasheet - Page 20

• Manufacturer Part Number: L6599ATD
• Description: IC RESONANT CONVRTR CTRLR 16SOIC
• Manufacturer: STMicroelectronics

Specifications of L6599ATD

• Applications: Resonant Converter Controller
• Voltage - Supply: 8.85 V ~ 16 V
• Current - Supply: 3.5mA
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 16-SOIC (3.9mm Width)
• Number Of Outputs: Single Output
• Output Voltage: 13.3 V
• Switching Frequency: 200 KHz
• Duty Cycle (max): 52 %
• Operating Supply Voltage: 8.85 V to 16 V
• Supply Current: 3.5 mA
• Maximum Operating Temperature: + 150 C
• Minimum Operating Temperature: - 40 C
• Fall Time: 30 ns
• Mounting Style: SMD/SMT
• Rise Time: 60 ns
• For Use With: 497-10542 - BOARD EVAL BASED ON L6599
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Input: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

Application information
20/31
Figure 11. Current sensing techniques: a) with sense resistor, b) “lossless”,
The L6599AT is equipped with a current sensing input (pin 6, ISEN) and a sophisticated
overcurrent management system. The ISEN pin is internally connected to the input of a first
comparator, referenced to 0.8 V, and to that of a second comparator referenced to 1.5 V. If
the voltage externally applied to the pin by either circuit in
comparator is tripped and this causes an internal switch to be turned on and the soft-start
capacitor C
oscillator frequency and thereby limits energy transfer. The discharge continues until the
voltage on the ISEN pin has dropped by 50 mV; this, with an averaging time in the range of
10/f
in a nearly constant peak primary current.
It is normal that the voltage on the ISEN pin could overshoot the 0.8 V. However, if the
voltage on the ISEN pin reaches 1.5 V, the second comparator is triggered and the L6599AT
shuts down and latches off with both the gate-drive outputs and the PFC_STOP pin low,
hence turning off the entire unit. The supply voltage of the IC must be pulled below the
UVLO threshold and then again above the start-up level in order to restart. Such an event
may occur if the soft-start capacitor C
enough, in cases of saturation of the transformer’s magnetizing inductance or a shorted
secondary rectifier.
In the circuit shown in
low-side MOSFET is used, note the specific connection of the resonant capacitor. In this
way, the voltage across Rs is related to the current flowing through the high-side MOSFET
and is positive most of the switching period, except for the time needed for the resonant
current to reverse after the low-side MOSFET has been switched off. Assuming that the time
constant of the RC filter is at least ten times the minimum switching frequency f
approximate value of Rs can be found using the empirical equation:
Equation 6
where I
and the primary winding of the transformer, which is related to the maximum load and the
minimum input voltage.
min
, ensures an effective frequency rise. Under output short-circuit, this operation results
Crpkx
SS
with capacitive shunt
is the maximum desired peak current flowing through the resonant capacitor
to be discharged (see
Figure 11
Doc ID 15534 Rev 3
a, where a sense resistor Rs in series with the source of the
Rs
=
Section 6.3: Soft-start
Vs
I
SS
Crpkx
pkx
is too large, preventing it from discharging fast
≈
5
I
Crpkx
⋅
0
8 .
≈
I
Crpkx
4
Figure 11
). This quickly increases the
exceeds 0.8 V, the first
min
, the
L6599AT