DN501 - 60V Buck-Boost Controller Drives High Power LEDs, Charges Batteries and Regulates Voltage with Up to 98.5% Efficiency at 100W and Higher

60V Buck-Boost Controller Drives High Power LEDs, Charges
Batteries and Regulates Voltage with Up to 98.5% Efficiency at
100W and Higher – Design Note 501
Keith Szolusha
Buck-Boost Controller Drives 100W LED String for
Airplane and Truck Lights
Airplanes and big trucks with 24V batteries need powerful, efficient and robust headlights and spotlights.
Figure 1 shows a 33.3V, 3A (nine Luminus SSR-90 LEDs)
VIN
15V TO 58V
RIN
0.003Ω
VIN
CVIN
1μF
TG1
INTVCC
BG1
LT3791
SHORTLED
OPENLED
OPENLED
PWM DIM
PWM
IVINMON
ISMON
CLKOUT
VREF
0.1μF
DIM
D2
4.7μF
10V
M2
0.1μF
L1 10μH
M4
1M
M3
34.2k
98
RLED
0.033Ω
SNSN
PGND
BG2
33.3VLED
3A
100W
FB
ISN
RT
SYNC VC
2.2k
10nF
86.6k
300kHz
D1: BAT46WJ
L1: COOPER HC9-100-R
M1, M2: RENESAS RJK0651DPB
M3-M5: RENESAS RJK0451DPB
LUMINUS
SST-90
w9
M5
DN501 F01
Figure 1. 15–58VIN to 33.3V 3A LED Driver with Up to 98.5% Efficiency
04/12/501
BUCK
96
BUCK-BOOST
95
94
92
TG2
PWMOUT
10nF
BOOST
97
93
SW2
ISP
CTRL
SGND
100
99
RSW
0.004Ω
10k
SS
COUT
4.7μF
50V
w5
SNSP
200k
SHORTLED
M1
SWI
EN/UVLO
OVLO
CIN
2.2μF
100V
w4
0.1μF
BST1
IVINP
499k
200k
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks
of Linear Technology Corporation. All other trademarks are the property of their
respective owners.
D1
470nF
43.2k
The solution in Figure 1 features up to 100:1 PWM dimming at 100Hz for accurate brightness adjustment without color shift and analog LED dimming when a PWM
oscillator is not present.
BST2
IVINN
27.4k
The 4-switch synchronous topology drives high power
LEDs with minimal switch power loss (and minimal
temperature rise). Unlike other topologies, the LT3791
buck-boost can be shorted from LED+ to both LED– and
GND and, as a feature, can be programmed to latch off
or keep trying to turn back on if the short is removed.
Diagnostic output flags report both short-circuit and
open-LED conditions.
INTVCC
INTVCC
50Ω
499k
buck-boost LED driver that runs from 15V to 58V input
with up to 98.5% efficiency.
EFFICIENCY (%)
Introduction
The LT®3791 is a 4-switch synchronous buck-boost
DC/DC converter that regulates both constant-current
and constant-voltage at up to 98.5% efficiency with a
single inductor. It can deliver hundreds of watts and
features a 60V input and output rating, making it ideal
for driving high power LED strings and charging high
voltage batteries when both step-up and step-down
conversion is needed. It can also be used as a constantvoltage buck-boost regulator with current limiting and
monitoring for both input and output.
91
90
33.3V
3A LEDs
10 15 20 25 30 35 40 45 50 55 60
DN501 F02
INPUT VOLTAGE (V)
Figure 2. Efficiency of
Figure 1
36V, 2.5A SLA Battery Charger
The buck-boost converter shown in Figure 3 charges a
36V 12Ah SLA battery at 44V with 2.5A DC from a 9V to
58V input.
Figure 1 can be easily turned into a 100W voltage regulator with VOUT between 6V and 55V by placing a 100k
resistor between the SS and VREF pins to defeat soft-start
reset during a fault.
Specially integrated C/10 current sensing and battery
voltage detection drops the battery voltage from its
charging voltage (44V) to its float voltage (41V) when
the battery is near full charge. The OPENLED flag is used
to change the state of the charger from charge to float.
When the battery voltage drops far enough, voltage feedback returns the charger to its charge state.
The voltage regulator is short-circuit proof. The
SHORTLED flag reports when there is a short circuit on
the output. The input current monitor can still be used in
constant-voltage regulation to protect any system that
is input-current limited. RLED sets the output current
limit for short circuit, but can be removed to provide
a PGOOD flag using OPENLED by shorting ISP to ISN.
The LT3791 can be tailored to charge a range of battery chemistries and capacities from a variety of input
sources regardless of the voltage relationship between
them. An external microcontroller can be programmed
and used to create a maximum power point tracking device to charge the battery from a solar panel. The output
diagnostics and dimming input pins make this a simple
interface for high power solar panel applications design.
Conclusion
The LT3791 synchronous buck-boost controller delivers 100W and higher power at up to 98.5% efficiency to
a number of different loads. The wide, 4.7V to 60V input
and 0V to 60V output voltage range make it both powerful and versatile, and its short-circuit capability makes
this a robust choice for many applications in potentially
hazardous environments. This seemingly limitless IC
can be used in applications where a typical buck or boost
converter cannot because of the crossover of input and
output voltage ranges.
120W, 6V to 55V Voltage Regulator
The LT3791 can also be used in high power constantvoltage buck-boost applications. The FB pin doubles
as both the main voltage feedback for the buck-boost,
and the overvoltage protection detection and regulation
when used as an LED driver.
PVIN
9V TO 58V
RIN
0.003Ω
VIN
1μF
INTVCC
D1
4.7μF
D2
BST2
50Ω
IVINN
TG1
IVINP
499k
BG1
OVLO
INTVCC
200k
30.9k
M1
LT3791
M4
0.1μF
SWI
EN/UVLO
COUT
4.7μF
50V
w2
0.1μF
BST1
470nF
57.6k
CIN
2.2μF
100V
w4
L1 10μH
M2
M3
SNSP
RS1
0.04Ω
RSW
0.004Ω
SHORTLED
PWMOUT
SNSN
+
PGND
IVINMON
ISMON
CLKOUT
CTRL
SGND
CHARGE CURRENT
CONTROL
BG2
SW2
TG2
FB
ISP
1μF
C8
0.1μF
SS
RT
SYNC VC
10nF
D1, D2: BAT46WJ
L1: WÜRTH 74435571100 10μH
M1-M5: RENESAS RJK0651DPB
1k
36V
SLA BATTERY
AGM TYPE
41V FLOAT
44V CHARGE
AT 25°C
50Ω
ISN
OPENLED
VREF
PWM
2.5A
CHARGE
1.00M
INTVCC
86.6k
300kHz
10k
402k
30.1k
M5
4.7nF
DN501 F03
Figure 3. 36V, 2.5A SLA Battery Charger with C/10 Charge Termination
Data Sheet Download
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For applications help,
call (408) 432-1900, Ext. 3801
Linear Technology Corporation
dn501f LT/AP 0412 196K • PRINTED IN THE USA
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