LM5116MH/NOPB National Semiconductor, LM5116MH/NOPB Datasheet - Page 15

• Manufacturer Part Number: LM5116MH/NOPB
• Description: IC CTRLR SYNCH BUCK 20-TSSOP
• Manufacturer: National Semiconductor
• Series: PowerWise®r
• Type: Step-Down (Buck)r

Specifications of LM5116MH/NOPB

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 1.22 ~ 80 V
• Current - Output: 20A
• Frequency - Switching: 50kHz ~ 1MHz
• Voltage - Input: 6 ~ 100 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 20-TSSOP Exposed Pad, 20-eTSSOP, 20-HTSSOP
• Dc To Dc Converter Type: Synchronous Buck Controller
• Pin Count: 20
• Input Voltage: 6 to 100V
• Output Voltage: 1.215 to 80V
• Output Current: 3.5A
• Package Type: TSSOP EP
• Mounting: Surface Mount
• Operating Temperature Classification: Automotive
• Operating Temperature (min): -40C
• Operating Temperature (max): 125C
• For Use With: LM5116-12EVAL - BOARD EVALUATION FOR LM5116-12LM5116EVAL - BOARD EVALUATION LM5116
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -
• Lead Free Status / Rohs Status: Compliant
• Other names: LM5116MH

is an immediate reduction in duty cycle. To further protect the
external switches during prolonged current limit conditions,
an internal counter counts clock pulses when in current limit.
When the counter detects 256 consecutive clock cycles, the
regulator enters a low power dissipation hiccup mode of cur-
rent limit. The regulator is shut down by momentarily pulling
UVLO low, and the soft-start capacitor discharged. The reg-
ulator is restarted with a full soft-start cycle once UVLO
charges back to 1.215V. This process is repeated until the
fault is removed. The hiccup off-time can be controlled by a
capacitor to ground on the UVLO pin. In applications with low
Using a current sense resistor in the source of the low-side
MOSFET provides superior current limit accuracy compared
to R
to the large variation of MOSFET R
and part-to-part variation. The CS and CSG pins should be
Kelvin connected to the current sense resistor or MOSFET
drain and source.
The peak current which triggers the current limit comparator
is:
Where t
threshold is the difference between the 1.6V reference at the
current limit comparator and the 0.5V offset at the current
sense amplifier. This offset at the current sense amplifier al-
lows the inductor ripple current to go negative by 0.5V / (A x
R
Current limit hysteresis prevents chatter around the threshold
when VCCX is powered from VOUT. When 4.5V < VCC <
5.8V, the 1.6V reference is increased to 1.72V. The peak cur-
rent which triggers the current limit comparator becomes:
S
) when running full synchronous operation.
DS(ON)
ON
sensing. R
is the on-time of the high-side MOSFET. The 1.1V
DS(ON)
sensing is far less accurate due
DS(ON)
FIGURE 8. Current Limit and Ramp Circuit
with temperature
15
output inductance and high input voltage, the switch current
may overshoot due to the propagation delay of the current
limit comparator. If an overshoot should occur, the sample-
and-hold circuit will detect the excess recirculating current. If
the sample-and-hold DC level exceeds the internal current
limit threshold, the buck switch will be disabled and skip puls-
es until the current has decayed below the current limit thresh-
old. This approach prevents current runaway conditions due
to propagation delays or inductor saturation since the inductor
current is forced to decay following any current overshoot.
This has the effect of a 10% fold-back of the peak current
during a short circuit when VCCX is powered from a 5V out-
put.
Soft-Start and Diode Emulation
The soft-start feature allows the regulator to gradually reach
the initial steady state operating point, thus reducing start-up
stresses and surges. The LM5116 will regulate the FB pin to
the SS pin voltage or the internal 1.215V reference, whichever
is lower. At the beginning of the soft-start sequence when SS
= 0V, the internal 10µA soft-start current source gradually in-
creases the voltage of an external soft-start capacitor (C
connected to the SS pin resulting in a gradual rise of FB and
the output voltage.
FIGURE 9. Diode Emulation Control
30007543
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30007544
SS
)