LM5007
Pin Description
PIN
1
2
NAME
SW
BST
Switching Node
Boost Boot–strap capacitor input
DESCRIPTION
APPLICATION INFORMATION
Power switching node. Connect to the LC output
filter.
An external capacitor is required between the BST
and the SW pins. A 0.01uF ceramic capacitor is
recommended. An internal diode between Vcc and
BST completes the Buck gate drive bias network.
A resistor between this pin and RTN determines the
variation of off time, along with the FB pin voltage,
per cycle while in current limit. The off time is preset
to 17uS if FB =0V and decreases as the FB pin
voltage increases.
This pin is connected to the inverting input of the
internal regulation comparator. The regulation
threshold is 2.5V.
A resistor between this pin and Vin sets the switch
on time as a function of Vin. The minimum
recommended on time is 300ns at the maximum
input voltage.
If an auxiliary voltage is available to raise the
voltage on this pin, above the regulation setpoint
(7V), the internal series pass regulator will
shutdown, reducing the IC power dissipation. Do not
exceed 14V. This output provides gate drive power
for the internal Buck switch. An internal diode is
provided between this pin and the BST pin. A local
0.1uF decoupling capacitor is recommended. Series
pass regulator is current limited to 10mA.
Recommended operating range: 9V to 75V
3
R
CL
Current Limit OFF time programming pin
Toff = 10
-5
/ (0.59 + (FB / 7.22 x 10
− 6
x R
CL
))
4
5
RTN
FB
Circuit Ground
Feedback Signal from Regulated Output
6
R
ON
On time set pin
Ton = 1.42 x 10
-10
R
ON
/ Vin
7
Vcc
Output from the internal high voltage bias
regulator. V
CC
is nominally regulated to 7 Volts.
8
Vin
Input supply voltage
3
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