Datasheet

FB
SW
RT
V
IN
BST
SD
5V
S
R
Q
Q
AGND
IS
CLK
+
SS
PRE
3, 4
2
11
7
6
5 8
9
12
10
13, 14
1
SD
Ir
LM5576
SHUTDOWN
STANDBY
7V
REGULATOR
SYNC
SYNC
OSCILLATOR
RAMP OUT
PGND
CLK
CLK
COMP
ERROR
AMP
R3
21k
C3
330p
C11
330p
R7
10
C9
22
C10
150
R6
1.65k
R5
5.11k
L1
33 PH
C7
0.022
C8
0.47
D1
CSHD6-100C
15, 16
19
17, 18
20
THERMAL
SHUTDOWN
UVLO
UVLO
CLK
DIS
VCC
LEVEL
SHIFT
DRIVER
1.225V
1.225V
0.7V
0.7V
R4
49.9k
C5
0.01
C6
open
R2
OPEN
C12
OPEN
C4
0.01
C2
2.2
C1
2.2
R1
OPEN
7V ± 75V
VIN
V
IN
2.1V
PWM
C_LIMIT
10 PA
5 PA
V
IN
TRACK
SAMPLE
and
HOLD
0.5V/A
RAMP GENERATOR
Ir = (5 PA x (V
IN
± V
OUT
))
+ 25 PA
LM5576, LM5576-Q1
SNVS447I –JANUARY 2007–REVISED APRIL 2013 www.ti.com
Typical Application Circuit and Block Diagram
Figure 9.
Detailed Operating Description
The LM5576 switching regulator features all of the functions necessary to implement an efficient high voltage
buck regulator using a minimum of external components. This easy to use regulator integrates a 75V N-Channel
buck switch with an output current capability of 3 Amps. The regulator control method is based on current mode
control utilizing an emulated current ramp. Peak current mode control provides inherent line voltage feed-forward,
cycle-by-cycle current limiting, and ease of loop compensation. The use of an emulated control ramp reduces
noise sensitivity of the pulse-width modulation circuit, allowing reliable processing of very small duty cycles
necessary in high input voltage applications. The operating frequency is user programmable from 50kHz to
500kHz. An oscillator synchronization pin allows multiple LM5576 regulators to self synchronize or be
synchronized to an external clock. The output voltage can be set as low as 1.225V. Fault protection features
include, current limiting, thermal shutdown and remote shutdown capability. The device is available in the
HTSSOP-20 package featuring an exposed pad to aid thermal dissipation.
The functional block diagram and typical application of the LM5576 are shown in Figure 9. The LM5576 can be
applied in numerous applications to efficiently step-down a high, unregulated input voltage. The device is well
suited for telecom, industrial and automotive power bus voltage ranges.
High Voltage Start-Up Regulator
The LM5576 contains a dual-mode internal high voltage startup regulator that provides the Vcc bias supply for
the PWM controller and boot-strap MOSFET gate driver. The input pin (VIN) can be connected directly to the
input voltage, as high as 75 Volts. For input voltages below 9V, a low dropout switch connects Vcc directly to
Vin. In this supply range, Vcc is approximately equal to Vin. For Vin voltage greater than 9V, the low dropout
switch is disabled and the Vcc regulator is enabled to maintain Vcc at approximately 7V. The wide operating
range of 6V to 75V is achieved through the use of this dual mode regulator.
The output of the Vcc regulator is current limited to 25mA. Upon power up, the regulator sources current into the
capacitor connected to the VCC pin. When the voltage at the VCC pin exceeds the Vcc UVLO threshold of 5.35V
and the SD pin is greater than 1.225V, the output switch is enabled and a soft-start sequence begins. The output
switch remains enabled until Vcc falls below 5.0V or the SD pin falls below 1.125V.
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Product Folder Links: LM5576 LM5576-Q1