STMicroelectronics 19 V - 90 W adapter with PFC for laptop computers using the L6563H and L6599A EVL6599A-90WADP EVL6599A-90WADP Ficha De Dados
Códigos do produto
EVL6599A-90WADP
Main characteristics and circuit description
AN3172
8/31
Doc ID 17230 Rev 1
1.5
Output voltage feedback loop
The feedback loop is implemented by means of a typical circuit using a TL431 modulating
the current in the optocoupler diode.
the current in the optocoupler diode.
On the primary side, R34 - connecting pin RFMIN (#4) to the optocoupler’s phototransistor -
closes the feedback loop and its value sets the maximum switching frequency at about 130
kHz. This value has been chosen to limit the switching losses at light-load operation. R31,
connecting the same pin to ground, sets the minimum switching frequency. The R-C series
R44 and C18 sets both soft-start maximum frequency and duration.
closes the feedback loop and its value sets the maximum switching frequency at about 130
kHz. This value has been chosen to limit the switching losses at light-load operation. R31,
connecting the same pin to ground, sets the minimum switching frequency. The R-C series
R44 and C18 sets both soft-start maximum frequency and duration.
1.6
L6599A overload and short-circuit protection
The current into the primary winding is sensed by the lossless circuit R41, C27, D11, D10,
R39, and C25 and it is fed into the ISEN pin (#6). In the case of overcurrent, the voltage on
the pin overpasses an internal comparator threshold (0.8 V), triggering a protection
sequence. The capacitor (C45) connected to the DELAY pin (#2) is charged by an internal
150 µA current generator and is slowly discharged by the external resistor (R24). If the
voltage on the pin reaches 2 V, the soft-start capacitor is completely discharged so that the
switching frequency is pushed to its maximum value. As the voltage on the pin exceeds 3.5
V the IC stops switching and the internal generator is turned off, so that the voltage on the
pin decays because of the external resistor. The IC is soft-restarted as the voltage drops
below 0.3 V. In this way, under short-circuit conditions, the converter works intermittently
with very low average input power.
R39, and C25 and it is fed into the ISEN pin (#6). In the case of overcurrent, the voltage on
the pin overpasses an internal comparator threshold (0.8 V), triggering a protection
sequence. The capacitor (C45) connected to the DELAY pin (#2) is charged by an internal
150 µA current generator and is slowly discharged by the external resistor (R24). If the
voltage on the pin reaches 2 V, the soft-start capacitor is completely discharged so that the
switching frequency is pushed to its maximum value. As the voltage on the pin exceeds 3.5
V the IC stops switching and the internal generator is turned off, so that the voltage on the
pin decays because of the external resistor. The IC is soft-restarted as the voltage drops
below 0.3 V. In this way, under short-circuit conditions, the converter works intermittently
with very low average input power.
1.7
PFC overvoltage and open-loop protection
Both circuit stages, PFC and resonant, are equipped with their own overvoltage protections.
The L6563H PFC controller monitors its output voltage via the resistor divider connected to
a dedicated pin (PFC_OK, #7) protecting the circuit in the case of loop failures or
disconnection of the feedback loop divider. In the case where a fault condition is detected,
the PFC_OK circuitry latches the L6563H operations and, by means of the PWM_LATCH
pin (#8), it also latches the L6599A, via the DIS pin (#8). The converter is kept latched by the
L6563H HV circuit that supplies the IC charging the Vcc capacitor periodically. To resume
converter operation mains restart is necessary.
a dedicated pin (PFC_OK, #7) protecting the circuit in the case of loop failures or
disconnection of the feedback loop divider. In the case where a fault condition is detected,
the PFC_OK circuitry latches the L6563H operations and, by means of the PWM_LATCH
pin (#8), it also latches the L6599A, via the DIS pin (#8). The converter is kept latched by the
L6563H HV circuit that supplies the IC charging the Vcc capacitor periodically. To resume
converter operation mains restart is necessary.