FAN5308MPX Fairchild Semiconductor, FAN5308MPX Datasheet - Page 8

• Manufacturer Part Number: FAN5308MPX
• Description: IC CONV DC-DC 800MA HI 3X3 6MLP
• Manufacturer: Fairchild Semiconductor
• Type: Step-Down (Buck), PWM - Current Moder

Specifications of FAN5308MPX

• Internal Switch(s): Yes
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 0.8 ~ 5.5 V
• Current - Output: 800mA
• Frequency - Switching: 1.3kHz
• Voltage - Input: 2.5 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: *
• Package / Case: 6-MLP
• Voltage - Supply: 2.5 V ~ 5.5 V
• Frequency-max: 1.3MHz
• Duty Cycle: 100%
• Pwm Type: Current Mode
• Buck: Yes
• Boost: No
• Flyback: No
• Inverting: No
• Doubler: No
• Divider: No
• Cuk: No
• Isolated: No
• Output Voltage: 0.8 V
• Mounting Style: SMD/SMT
• Operating Temperature Range: - 40 C to + 85 C
• Primary Input Voltage: 5.5V
• No. Of Outputs: 1
• Output Current: 800mA
• No. Of Pins: 6
• Peak Reflow Compatible (260 C): Yes
• Rohs Compliant: Yes
• Leaded Process Compatible: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

©2005 Fairchild Semiconductor Corporation
FAN5308 Rev. 1.0.2
The N-channel transistor is turned off before the inductor
current becomes negative. At this time, the P-channel is
switched on again, starting the next pulse. The converter
continues these pulses until the high threshold (typical
1.6% above nominal value) is reached. A higher output
voltage in PFM mode gives additional headroom for the
voltage drop during a load transient from light to full load.
The voltage overshoot during this load transient is also
minimized due to active regulation during turn on of the
N-channel rectifier switch. The device stays in sleep
mode until the output voltage falls below the low thresh-
old. The FAN5308 enters the PWM mode as soon as the
output voltage can no longer be regulated in PFM with
constant peak current.
100% Duty Cycle Operation
As the input voltage approaches the output voltage and
the duty cycle exceeds the typical 95%, the converter
turns the P-channel transistor continuously on. In this
mode, the output voltage is equal to the input voltage,
minus the voltage drop across the P-channel transistor:
where:
R
I
R
V
LOAD
dsON
L
OUT
= Inductor DC resistance
= Output current
= V
= P-channel switch on resistance
IN
– I
LOAD
(R
dsON
+ R
L
)
EQ. 2
8
UVLO and Soft Start
The reference and the circuit remain reset until the V
crosses its UVLO threshold.
The FAN5308 has an internal soft-start circuit that limits
the inrush current during start-up. This prevents possible
voltage drops of the input voltage and eliminates the out-
put voltage overshoot. The soft-start is implemented as a
digital circuit, increasing the switch current in four steps
to the P-channel current limit (1500mA). Typical start-up
time for a 20µF output capacitor and a load current of
800mA is 800µs.
Short-Circuit Protection
The switch peak current is limited cycle-by-cycle to a typ-
ical value of 1500mA. In the event of an output voltage
short circuit, the device operates with a frequency of
400kHz and minimum duty cycle; therefore, the average
input current is typically 200mA.
Thermal Shutdown
When the die temperature exceeds 150°C, a reset
occurs and remains in effect until the die cools to 130°C.
At that time, the circuit is allowed to restart.
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IN