LM5010MH/NOPB National Semiconductor, LM5010MH/NOPB Datasheet - Page 12

• Manufacturer Part Number: LM5010MH/NOPB
• Description: IC BUCK ADJ 1A 14TSSOP
• Manufacturer: National Semiconductor
• Type: Step-Down (Buck)r

Specifications of LM5010MH/NOPB

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 2.5 ~ 70 V
• Current - Output: 1A
• Frequency - Switching: 1MHz
• Voltage - Input: 8 ~ 75 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 14-TSSOP Exposed Pad, 14-eTSSOP 14-HTSSOP
• Primary Input Voltage: 75V
• No. Of Outputs: 1
• Output Voltage: 70V
• Output Current: 1A
• Voltage Regulator Case Style: TSSOP
• No. Of Pins: 14
• Operating Temperature Range: -40°C To +125°C
• Svhc: No SVHC (15-Dec-2010)
• Rohs Compliant: Yes
• Dc: 1030
• For Use With: LM5010 EVAL - BOARD EVALUATION LM5010
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -
• Other names: *LM5010MH; *LM5010MH/NOPB; LM5010MH

www.national.com
Current Limit
Current limit detection occurs during the off-time by monitor-
ing the recirculating current through the free-wheeling diode
(D1). The detection threshold is 1.25A,
Figure 1, when the buck switch is off the inductor current
flows through the load, into S
out of I
threshold the current limit comparator output switches to
delay the start of the next on-time period. The next on-time
starts when the current out of I
the voltage at FB is below 2.5V. If the overload condition
persists causing the inductor current to exceed the threshold
during each on-time, that is detected at the beginning of
each off-time. The operating frequency is lower due to
longer-than-normal off-times.
Figure 12 illustrates the inductor current waveform. During
normal operation the load current is I
ripple waveform. When the load resistance decreases the
The current limit threshold can be increased by connecting
an external resistor (R
external resistor typically is less than 1Ω, and its calculation
is explained in the Applications Information section.
The peak current out of SW and I
The average current out of SW must be less than 3A, and
the average current out of I
N - Channel Buck Switch and
Driver
The LM5010 integrates an N-Channel buck switch and as-
sociated floating high voltage gate driver. The peak current
through the buck switch must not be allowed to exceed 3.5A,
and the average current must be less than 3A. The gate
driver circuit is powered by the external bootstrap capacitor
between BST and SW (C4). During each off-time, the SW pin
is at approximately -1V, and C4 is re-charged from V
through the internal high voltage diode. The minimum off-
time of 265 ns ensures a minimum time each cycle to
recharge the bootstrap capacitor. A 0.022 µF ceramic ca-
pacitor is recommended for C4.
SEN
and through D1. If that current exceeds the
CL
) between S
SEN
GND
SEN
must be less than 2A.
, through the sense resistor,
SEN
is below the threshold and
FIGURE 12. Inductor Current - Current Limit Operation
must not exceed 3.5A.
O
±
, the average of the
GND
0.25A. Referring to
and I
SEN
. The
CC
12
current ratchets up until the lower peak attempts to exceed
the threshold. During the Current Limited portion of Figure
12, the current ramps down to the threshold during each
off-time, initiating the next on-time (assuming the voltage at
FB is
amount equal to:
During this time the LM5010 is in a constant current mode,
with an average load current (I
∆I/2.
The “valley current limit” technique allows the load current to
exceed the current limit threshold as long as the lower peak
of the inductor current is less than the threshold.
Softstart
The softstart feature allows the converter to gradually reach
a steady state operating point, thereby reducing startup
stresses and current surges. Upon turn-on, after V
reaches the under-voltage threshold (t1 in Figure 8), an
internal 11.5 µA current source charges the external capaci-
tor at the Softstart pin to 2.5V (t2 in Figure 8). The ramping
voltage at SS (and at the non-inverting input of the regulation
comparator) ramps up the output voltage in a controlled
manner. This feature keeps the load current from going to
current limit during startup, thereby reducing inrush currents.
An internal switch grounds the Softstart pin if V
the under-voltage lockout threshold, if a thermal shutdown
occurs, or if the circuit is shutdown using the R
Thermal Shutdown
The LM5010 should be operated so the junction temperature
does not exceed 125˚C. If the junction temperature in-
creases above that, an internal Thermal Shutdown circuit
activates (typically) at 175˚C, taking the controller to a low
power reset state by disabling the buck switch and the
on-timer, and grounding the Softstart pin. This feature helps
prevent catastrophic failures from accidental device over-
<
2.5V). During each on-time the current ramps up an
OCL
) equal to the threshold +
20119920
ON
CC
/SD pin.
is below
(6)
CC