FAN302HLMY Datasheet, PDF (14/18 Pages) Fairchild Semiconductor – PWM Controller for Low Standby Power Battery- Charger Applications — mWSaver™ Technology

V_DD Over-Voltage Protection
V_DD over-voltage protection prevents IC damage from
over-voltage exceeding the IC voltage rating. When the
V_DD voltage exceeds 26.5V due to an abnormal
condition, the protection is triggered. This protection is
typically caused by open circuit in the secondary-side
feedback network.
V_S Over-Voltage Protection (OVP)
V_S over-voltage protection prevents damage due to
output over-voltage conditions. Figure 39 shows the V_S
OVP protection method. When abnormal system
conditions occur that cause V_S to exceed 2.8V, after a
period of debounce time; PWM pulses are disabled and
FAN302HLMY_F117 enters Latch Mode until VDD drops
under VDD-LH. By that time, PWM pulses revive. V_S over-
voltage conditions are usually caused by open circuit of
the secondary-side feedback network or abnormal
behavior by the VS pin divider resistor.
Figure 37. Auto-Restart Mode Operation
Figure 38. Latch-Mode Operation
Over-Temperature Protection (OTP)
The temperature-sensing circuit shuts down PWM
output if the junction temperature exceeds 140°C (t_OTP).
Figure 39. V_S OVP Protection
Leading-Edge Blanking (LEB)
Each time the power MOSFET is switched on, a turn-on
spike occurs at the sense resistor. To avoid premature
termination of the switching pulse, a 150ns leading-edge
blanking time is built in. Conventional RC filtering can
therefore be omitted. During this blanking period, the
current-limit comparator is disabled and it cannot switch
off the gate driver.
Noise Immunity
Noise from the current sense or the control signal can
cause significant pulse-width jitter. While slope
compensation helps alleviate these problems, further
precautions should still be taken. Good placement and
layout practices should be followed. Avoid long PCB
traces and component leads. Locate bypass filter
components near the PWM IC.
© 2012 Fairchild Semiconductor Corporation
FAN302HLMY_F117 • Rev. 1.0.1
14
www.fairchildsemi.com