FAN5234QSCX_NL Fairchild Semiconductor, FAN5234QSCX_NL Datasheet - Page 5

• Manufacturer Part Number: FAN5234QSCX_NL
• Manufacturer: Fairchild Semiconductor

Specifications of FAN5234QSCX_NL

• Dc To Dc Converter Type: Synchronous Buck Controller/PWM DC to DC Controller
• Number Of Outputs: 1
• Pin Count: 16
• Input Voltage: 5 to 24V
• Output Voltage: 0.9 to 5.5V
• Package Type: QSOP
• Mounting: Surface Mount
• Operating Temperature Classification: Commercial
• Operating Temperature (min): -10C
• Operating Temperature (max): 85C
• Lead Free Status / Rohs Status: Compliant

Circuit Description
Overview
The FAN5234 is a PWM controller intended for low voltage
power applications in modern notebook, desktop, and
sub-notebook PCs. The output voltage of the controller can
be set in the range of 0.9V to 5.5V by an external resistor
divider.
The synchronous buck converter can operate from either an
unregulated DC source (such as a notebook battery) with
voltage ranging from 2V to 24V, or from a regulated system
rail. In either mode of operation the IC is biased from a +5V
source. The PWM modulator uses an average current mode
control with input voltage feed-forward for simplified feed-
back loop compensation and improved line regulation. The
controller includes integrated feedback loop compensation
that dramatically reduces the number of external compo-
nents.
Depending on the load level, the converter can operate either
in fixed frequency PWM mode or in a hysteretic mode.
Switch-over from PWM to hysteretic mode improves the
converters' efficiency at light loads and prolongs battery run
time. In hysteretic mode, a comparator is synchronized to the
main clock that allows seamless transition between the oper-
ational modes and reduced channel-to-channel interaction.
FAN5234
REV. 1.0.10 5/3/04
VIN
EN
FPWM
SS
VSEN
PGOOD
REF2
SS
Reference and
HYST
Soft Start
OSC
CLK
EA
OVP
RAMP
VREF
S
POR/UVLO
Q
R
CLAMP
CYCLE
DUTY
PWM
PWM/HYST
Figure 2. IC Block Diagram
RAMP
Σ
FPWM
HYST
PWM
CONTROL LOGIC
ILIM det.
CURRENT PROCESSING
I
OU T
VDD
The hysteretic mode of operation can be inhibited indepen-
dently using the FPWM pin if variable frequency operation is
not desired.
Oscillator
Table 1. Converter Operating modes
When VIN is from the battery, the oscillator's ramp ampli-
tude is proportional to VIN, providing voltage feed-forward
control for improved loop response. When in either of the
Fixed modes, oscillator's ramp amplitude is fixed. The oper-
ating frequency is then determined according to the connec-
tion on the VIN pin (Table 1).
Initialization and Soft Start
Assuming EN is high, FAN5234 is initialized when VCC
exceeds the rising UVLO threshold. Should VCC drop below
the UVLO threshold, an internal Power-On Reset function
disables the chip.
ADAPTIVE
Battery
Fixed
300
Fixed
600
PWM/HYST
Mode
GATE
5V
MODE
S/H
(Khz)
F
300
300
600
SW
VDD
ILIM
< 5.5V Fixed
< 5.5V Fixed
Converter
2 to 24V
Power
BOOT
HDRV
SW
LDRV
PGND
ISNS
PRODUCT SPECIFICATION
Q1
Q2
R
SENSE
VIN
C
BOOT
100K Ω to GND
Battery (>5V)
L
OU T
VIN Pin
GND
VOUT
C
OUT
5