FAN5235 Fairchild Semiconductor, FAN5235 Datasheet - Page 10

• Manufacturer Part Number: FAN5235
• Description: System Electronics Regulator for Mobile PCs
• Manufacturer: Fairchild Semiconductor

FAN5235
Error Amplifier output voltage clamp
During a load transient the error amplifier voltage is allowed
full swing. After two clock cycles, if the amplifier is still out
of range the voltage and consequently the duty cycle (DC) is
clamped. The DC clamp automatically limits the build up of
over-currents during abnormal conditions, including short
circuits:
Thermal shutdown
If the die temperature of the FAN5235 exceeds safe limits,
the IC shuts itself off. When the over-temperature (OT)
event ends, the IC comes back to normal operation. There is
a 25°C thermal hysteresis between shutdown and start up.
Generic Mobile System Block Diagram
10
Vclamp=0.5V+
+Vo/8 +/-0.2V
VFB=0.5V+Vo/8
VREF
SDN5
SDN3.3
PGOOD
Figure 6. Duty-Cycle Clamp
–
EA
+
P CODE EXECUTION
FAN5235
2 Cycles
Counter
0.4V
SDWN
V RAMP =0.5V+Vin/8
5V
3.3V
5V-Always
3.3V-Always
Figure 7. System Block Diagram
–
+
PGOOD
EN
8051
C
C
Vin=5.6 to 24V
Input UVLO
If the input voltage falls below the UVLO threshold, the
FAN5235 turns itself off and stays off as long as Input
voltage is below threshold.
IC Protections Table
* Only the converter in Over-Voltage goes in SOFT CROW-
BAR mode.
OC/UV
(Bucks)
OC/UV
(LDO)
OV (Buck)*
OV (Boost)
SDWN=0
OT
UV (Boost)
OC (Boost)
SDWN
RC5231
OFF-LATCH OFF-LATCH
OFF-LATCH OFF-LATCH
HSD
Buck
Vcpu
1.5V
2.5V
OFF
OFF
OFF
ON
ON
"
RESET
LOGIC
Clock
CROWBAR
LSD
Buck
P
SOFT
OFF
OFF
ON
ON
"
PGOOD
CPU
CPU
OFF-LATCH
LDO
OFF
OFF
REV. 1.3.3 1/3/02
ON
ON
ON
ON
ON
OFF-LATCH
OFF-LATCH
LSD
Boost
33% DC
OFF
OFF
OFF
ON
"