FAN5236QSC Fairchild Semiconductor, FAN5236QSC Datasheet - Page 11

• Manufacturer Part Number: FAN5236QSC
• Description: IC CTRLR DDR/PWM DUAL HE 28QSOP
• Manufacturer: Fairchild Semiconductor

Specifications of FAN5236QSC

• Applications: Controller, Mobile-Friendly DDR
• Voltage - Input: 5 ~ 24 V
• Number Of Outputs: 2
• Voltage - Output: 0.9 ~ 5 V
• Operating Temperature: -10°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 28-QSOP
• Operating Temperature Range: - 10 C to + 85 C
• Mounting Style: SMD/SMT
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: FAN5236QSC_NL; FAN5236QSC_NL

FAN5236
Hysteretic Mode
Conversely, the transition from Hysteretic mode to PWM
mode occurs when the SW node is negative for 8 consecutive
cycles.
A sudden increase in the output current will also cause a
change from hysteretic to PWM mode. This load increase
causes an instantaneous decrease in the output voltage due to
the voltage drop on the output capacitor ESR. If the load
causes the output voltage (as presented at VSNS) to drop
below the hysteretic regulation level (20mV below VREF),
the mode is changed to PWM on the next clock cycle.
In hysteretic mode, the PWM comparator and the error
amplifier that provide control in PWM mode are inhibited
and the hysteretic comparator is activated. In hysteretic
mode the low side MOSFET is operated as a synchronous
rectifier, where the voltage across ( V
and it is switched off when V
flowing back from the load) allowing the diode to block
reverse conduction.
The hysteretic comparator initiates a PFM signal to turn on
HDRV at the rising edge of the next oscillator clock, when
the output voltage (at VSNS) falls below the lower threshold
(10mV below VREF) and terminates the PFM signal when
VSNS rises over the higher threshold (5mV above VREF).
REV. 1.1.9 7/12/04
C
SS
VSEN
SS
300K
Reference and
Soft Start
DS(ON)
ILIM det.
1.5M
TO PWM COMP
goes positive (current
DS(ON)
0.17pf
17pf
Figure 11. Current Limit / Summing Circuits
) it is monitored,
4.14K
2.5V
ILIM*11.2
I2 =
The switching frequency is primarily a function of:
1.
2.
3.
A transition back to PWM (Continuous Conduction Mode or
CCM) mode occurs when the inductor current rises suffi-
ciently to stay positive for 8 consecutive cycles. This occurs
when:
where V
series resistance of C
Because of the different control mechanisms, the value of the
load current where transition into CCM operation takes place
is typically higher compared to the load level at which transi-
tion into hysteretic mode occurs. Hysteretic mode can be
disabled by setting the FPWM pin low.
Spread between the two hysteretic thresholds
I
Output Inductor and Capacitor ESR
ISNS
LOAD
I
LOAD CCM
HYSTERESIS
V to I
0.9V
ILIM
S/H
ISNS
=
OUT
-------------------------------------- -
= 15mV and ESR is the equivalent
V
HYSTERESIS
.
2 ESR
in +
in –
PRODUCT SPECIFICATION
LDRV
PGND
ISNS
ILIM
R
R
SENSE
ILIM
(3)
11