L6699D STMicroelectronics, L6699D Datasheet - Page 24

• Manufacturer Part Number: L6699D
• Description: AC/DC Switching Converters Enhanced High Volt Res CTRL 600V
• Manufacturer: STMicroelectronics
• Type: High Voltage Controllersr

Specifications of L6699D

• Product Category: AC/DC Switching Converters
• Output Voltage: 13.3 V
• Input / Supply Voltage (max): 8.85 V
• Input / Supply Voltage (min): 16 V
• Switching Frequency: 235 kHz
• Supply Current: 3 mA
• Operating Temperature Range: - 25 C to + 125 C
• Mounting Style: SMD/SMT
• Package / Case: SO-16
• Number Of Outputs: 1
• Output Current: 800 mA

Current sensing, OCP and OLP
8
Note:
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Current sensing, OCP and OLP
In the L6699 the current sense input ISEN (pin 6) senses the current flowing in the resonant
tank to perform multiple tasks:
1.
2.
3.
In this section the discussion is concentrated on the OCP function.
Unlike PWM-controlled converters, where energy flow is controlled by the duty cycle of the
primary switch (or switches), in a resonant half bridge the duty cycle is fixed and energy flow
is controlled by its switching frequency. This has an impact on the way current limitation can
be realized. While in PWM-controlled converters energy flow can be limited simply by
terminating switch conduction in advance when the sensed current exceeds a preset
threshold (cycle-by-cycle limitation), in a resonant half bridge the most efficient way to
reduce an excessive current level is to increase the switching frequency, i.e. the oscillator
frequency.
In
The L6699 must sense the instantaneous tank current for proper operation of the smooth
startup function and the capacitive-mode detection circuit. Therefore, if a smoothing RC
circuit (the one shown in the dashed box) is used to reduce the noise level on the ISEN pin,
its time constant RF CF should be in the range of 100 - 200 ns. With slightly longer time
constants it is recommended that converter operation close to the capacitive-mode
boundary and during short-circuit, as well as at the end of the smooth-start phase, be
checked for possible hard-switching cycles. With considerably longer time constants (> 200
ns) hard-switching under the above mentioned conditions becomes very likely.
Figure 18. Current sensing techniques
Figure 18
Primary overcurrent protection (OCP function).
Hard-switching cycles prevention at startup (see
Capacitive-mode detection during operation (see
function
).
and
with sense resistor
19
a couple of current sensing methods are illustrated.
Doc ID 022835 Rev 2
Figure 19. Current sensing techniques
Section 6.3: Safe-start procedure
Section 9: Capacitive-mode detection
“lossless”, with capacitive
shunt
L6699
).