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Linear Technology LTC3703-5 Manual

60v synchronous switching regulator controller
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FEATURES
■
High Voltage Operation: Up to 60V
Ω
■
Large 1
Gate Drivers (with 5V Supply)
■
No Current Sense Resistor Required
■
Step-Up or Step-Down DC/DC Converter
■
Dual N-Channel MOSFET Synchronous Drive
■
Excellent Line and Load Transient Response
■
Programmable Constant Frequency: 100kHz to
600kHz
±1% Reference Accuracy
■
■
Synchronizable up to 600kHz
■
Selectable Pulse Skip Mode Operation
■
Low Shutdown Current: 25µA Typ
■
Programmable Current Limit
■
Undervoltage Lockout
■
Programmable Soft-Start
■
16-Pin Narrow SSOP and 28-Pin SSOP Packages
U
APPLICATIO S
■
48V Telecom and Base Station Power Supplies
■
Networking Equipment, Servers
■
Automotive and Industrial Control
, LTC and LT are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
*U.S. Patent Numbers: 5408150, 5055767, 6677210, 5847554, 5481178, 6304066, 6580258;
Others Pending.
TYPICAL APPLICATIO
High Efficiency High Voltage Step-Down Converter
30k
10k
1000pF
470pF
12k
21.5k
1%
0.1µF
100Ω
113k
1%
2200pF
V
CC
5V
+
22µF
MMDL770T1
MODE/SYNC
V
IN
FSET
BOOST
COMP
TG
0.1µF
LTC3703-5
FB
SW
I
V CC
MAX
10Ω
INV
DRV
CC
RUN/SS
BG
10µF
GND
BGRTN
1µF
Switching Regulator Controller
DESCRIPTIO
®
The LTC
3703-5 is a synchronous step-down switching
regulator controller that can directly step-down voltages
from up to 60V input, making it ideal for telecom and au-
tomotive applications. The LTC3703-5 drives external logic
level N-channel MOSFETs using a constant frequency (up
to 600kHz), voltage mode architecture.
A precise internal reference provides 1% DC accuracy. A
high bandwidth error amplifier and patented* line feed
forward compensation provide very fast line and load
transient response. Strong 1Ω gate drivers allow the
LTC3703-5 to drive multiple MOSFETs for higher current
applications. The operating frequency is user program-
mable from 100kHz to 600kHz and can also be synchro-
nized to an external clock for noise-sensitive applications.
Current limit is programmable with an external resistor
and utilizes the voltage drop across the synchronous
MOSFET to eliminate the need for a current sense resistor.
For applications requiring up to 100V operation, refer to
the LTC3703 data sheet.
PARAMETER
Maximum V
IN
MOSFET Gate Drive
+
V
UV
CC
–
V
UV
CC
V
IN
6V TO 60V
+
22µF
×2
Si7850DP
8µH
V
OUT
5V
5A
+
270µF
16V
Si7850DP
D1
MBR1100
37035 TA04
LTC3703-5
60V Synchronous
LTC3703-5
LTC3703
60V
100V
4.5V to 15V
9.3V to 15V
3.7V
8.7V
3.1V
6.2V
Efficiency vs Load Current
100
V
= 12V
IN
V
IN
95
V
= 42V
IN
90
85
80
1
3
0
2
4
LOAD CURRENT (A)
= 24V
5
37053 TA04b
37035fa
1

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Summary of Contents for Linear Technology LTC3703-5

  • Page 1 100V MOSFET Gate Drive 4.5V to 15V 9.3V to 15V , LTC and LT are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. 3.7V 8.7V *U.S. Patent Numbers: 5408150, 5055767, 6677210, 5847554, 5481178, 6304066, 6580258;...

  • Page 2: Electrical Characteristics

    LTC3703-5 ABSOLUTE AXI U RATI GS (Note 1) Supply Voltages MODE/SYNC, INV Voltages ....... –0.3V to 15V , DRV .......... –0.3V to 15V , FB, I , COMP Voltages ....–0.3V to 3V (DRV – BGRTN), (BOOST – SW) ..–0.3V to 15V Driver Outputs BOOST (Continuous) ......
  • Page 3 • 100 °C/W) G Package LTC3703-5: T + (P temperature may impair device reliability. Note 4: The LTC3703-5 is tested in a feedback loop that servos V to the Note 8: R guaranteed by correlation to wafer level measurement. DS(ON)
  • Page 4 LTC3703-5 TYPICAL PERFOR A CE CHARACTERISTICS = 25°C (unless otherwise noted). Load Transient Response Efficiency vs Input Voltage Efficiency vs Load Current = 24V 50mV/DIV = 42V = 1A AC COUPLED = 5A 2A/DIV = 5V = 12V 50µs/DIV = 50V...
  • Page 5 LTC3703-5 TYPICAL PERFOR A CE CHARACTERISTICS Driver Pull-Down R Driver Peak Source Current Driver Peak Source Current DS(ON) vs Temperature vs Temperature vs Supply Voltage = 5V = 5V 12.5 –60 –40 –20 0 20 40 60 80 100 120 140 –60 –40 –20 0...
  • Page 6 LTC3703-5 TYPICAL PERFOR A CE CHARACTERISTICS Max % DC vs Frequency and Current vs Temperature Temperature % Duty Cycle vs COMP Voltage = 10V = 50V –45°C = 25V 25°C 90°C 125°C 0.75 1.00 1.25 1.50 1.75 2.00 –60 –40 –20 0...
  • Page 7 RUN/SS (Pin 7/Pin 13): Run/Soft-Start. Pulling RUN/SS be- tky diode from DRV to BOOST will create a complete float- low 0.9V will shut down the LTC3703-5, turn off both of the ing charge-pumped supply at BOOST. external MOSFET switches and reduce the quiescent sup- (Pin 16/Pin 1): Input Voltage Sense Pin.
  • Page 8 Diagram of the IC and the circuit on the first page of this controller for DC/DC step-down converters. It is designed data sheet. The LTC3703-5 uses voltage mode control in to be used in a synchronous switching architecture with which the duty ratio is controlled directly by the error two external N-channel MOSFETs.
  • Page 9 DRV pin. The LTC3703-5 uses a fast 25MHz op amp as an error am- The top MOSFET drivers are biased from floating boot- plifier. This allows the compensation network to be opti-...
  • Page 10 4V clamp. Then the MIN feedback comparator gate up 2V before the V of the bottom MOSFET has more is enabled and the LTC3703-5 is in full operation. When the than 0V across it. RUN/SS is low, the supply current is reduced to 25µA.
  • Page 11 = 42V Pulse Skip Mode The LTC3703-5 can operate in one of two modes select- able with the MODE/SYNC pin—Pulse Skip Mode or = 12V forced continuous mode. Pulse Skip Mode is selected = 42V when increased efficiency at light loads is desired.
  • Page 12 BG driving the synchronous (bottom side) MOSFET. In boost mode, however, the peak MOSFET switch. If the INV pin is pulled above 2V, the LTC3703-5 operates in boost mode with BG driving the main (bottom current does not equal the load current but instead /(1 –...
  • Page 13 MOSFET should be used for the top MOSFET in Inductor applications that have an output voltage that is less than The inductor in a typical LTC3703-5 circuit is chosen for 1/3 of the input voltage. In applications where V >> V a specific ripple current and saturation current.
  • Page 14 APPLICATIO S I FOR ATIO appropriate breakdown specification. Since most MOSFETs MainSwitchDutyCycle in the 30V to 60V range have logic level thresholds ≥ 4.5V), the LTC3703-5 is designed to be used GS(MIN) – with a 4.5V to 15V gate drive supply (DRV pin).
  • Page 15 ESR of C until the feedback loop in the LTC3703-5 can Because tantalum and OS-CON capacitors are not avail- change the inductor current to match the new load current...
  • Page 16 An external bootstrap capacitor, C , connected to the BOOST pin supplies the gate drive voltage for the topside The LTC3703-5 output voltage is set by a resistor divider MOSFETs. Capacitor C is charged through external according to the following formula:...
  • Page 17 Figure 9d. Capacitive Charge Pump for V < 40V) current to flow at full reverse voltage. If the reverse below the UVLO threshold, the LTC3703-5 shuts down current times reverse voltage exceeds the maximum and the gate drive outputs remain low.
  • Page 18 The is the same as the output current. The LTC3703-5 current modulator consists of the internal PWM generator, the limit circuit inverts the negative voltage across the MOSFET...
  • Page 19 LC roll-off. As with a Type 2 circuit, the loop should cross through 0dB in the middle of the GAIN phase bump to maximize phase margin. Many LTC3703-5 circuits using low ESR tantalum or OS-CON output capaci- –...
  • Page 20 *this file written to run with PSpice 8.0 to give a working system. To measure the modulator gain *may require modifications for other and phase directly, wire up a breadboard with an LTC3703-5 SPICE simulators and the actual MOSFETs, inductor and input and output *MOSFETs capacitors that the final design will use.
  • Page 21 (this converts GAIN in dB to G in shown in the Typical Applications section. To operate the absolute gain) LTC3703-5 in boost mode, the INV pin should be tied to TYPE 2 Loop: the V voltage (or a voltage above 2V). Note that in boost mode, pulse-skip operation and the line feedforward com- ⎛...
  • Page 22 IN MIN ≈ • RMS COUT O MAX The LTC3703-5 provides current limiting in boost mode by IN MIN monitoring the V of the main switch during its on-time and comparing it to the voltage at I . To set the current...
  • Page 23 The RUN/SS pin is a multipurpose pin that provide a soft- Compensating a voltage mode boost converter is unfortu- start function and a means to shut down the LTC3703-5. nately more difficult than for a buck converter. This is due Soft-start reduces the input supply’s surge current by...
  • Page 24 ⎝ ⎠ The start delay can be reduced by using diode D1 in Figure 18. where R1 and R2 are shown in Figure 9c. If the LTC3703-5 is operating in Pulse Skip Mode and the 3.3V OR 5V RUN/SS RUN/SS...
  • Page 25 ON(MIN) losses, four main sources usually account for most of the that the LTC3703-5 is capable of turning the top MOSFET losses in LTC3703-5 circuits: 1) LTC3703-5 V current, on and off again. It is determined by internal timing delays...
  • Page 26 Loop compensation has a fundamental impact on tran- subjected to a 1A to 5A load transient. Initially, the loop is sient recovery time, the time it takes the LTC3703-5 to in regulation and the DC current in the output capacitor is recover after the output voltage has dropped due to a load zero.

  • Page 27: Measurement Techniques

    Solder the MOSFET and the resistor(s) as close to ating a suitable transient to test the circuit. Output mea- the output of the LTC3703-5 circuit as possible and set up surements should be taken with a scope probe directly the signal generator to pulse at a 100Hz rate with a 5% duty across the output capacitor.
  • Page 28 1. Keep the signal and power grounds separate. The signal twice as long each period (almost 100% of the period in ground consists of the LTC3703-5 GND pin, the ground short circuit) as the top MOSFET, use two Si7850DP return of C , and the (–) terminal of V...
  • Page 29 This Place the divider resistors near the LTC3703-5 in order to also helps keep the signal ground and power ground keep the high impedance FB node short.
  • Page 30 LTC3703-5 TYPICAL APPLICATIO S 15V-60V Input Voltage to 12V/10A Step-Down Converter with Pulse Skip Mode Enabled 5V TO 15V 22µF 15V TO 60V MMDL770T1 MODE/SYNC 22µF 100V FSET BOOST ×2 Si7850DP COMP 0.1µF 470pF 1000pF 8µH LTC3703-5 220µF 10Ω ×2 8.06k...
  • Page 31 Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen- tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.

  • Page 32: Related Parts

    ≤ 60V, Current Mode, 1.23V ≤ V ≤ 36V LT3800 60V Synchronous DC/DC Controller 37035fa LT/LT 0505 REV A • PRINTED IN USA Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 © LINEAR TECHNOLOGY CORPORATION 2004 (408) 432-1900 FAX: (408) 434-0507 www.linear.com ● ●...

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