LM5088
June 8, 2009 Wide Input Range Non-Synchronous Buck Controller
General Description
The LM5088 high voltage non-synchronous buck controller features all the necessary functions to implement an efficient high voltage buck converter using a minimum number of ex-ternal components. The LM5088 can be configured to operate over an ultra-wide input voltage range of 4.5V to 75V. This easy to u controller includes a level shifted gate driver ca-pable of controlling an external N-channel buck switch. The control method is bad upon peak current mode control uti-lizing an emulated current ramp. The u of an emulated control ramp reduces noi nsitivity of the pul-width mod-ulation circuit, allowing reliable control of very small duty cycles necessary in high input voltage/low output voltage ap-plications. The LM5088 switching frequency is programmable from 50 kHz to 1 MHz.
The LM5088 is available in two versions: The LM5088-1 pro-vides a +/-5% frequency dithering function to reduce the conducted and radiated EMI, while the LM5088-2 provides a versatile restart timer for overload protection. Additional fea-tures include a low dropout bias regulator, tri-level enable input to control shutdown and standby modes, soft-start and oscillator synchronization capability. The device is
available in a thermally enhanced TSSOP-16EP pin package.Features
■Emulated current mode control
■Drives external high-side N-channel MOSFET
■Ultra-wide input voltage range from 4.5V to 75V
■Low I Q Shutdown and Standby modes
■High duty cycle ratio feature for reduced dropout voltage ■Spread spectrum EMI reduction (LM5088-1)
■Hiccup timer for overload protection (LM5088-2)
■Adjustable output voltage from 1.205V with 1.5% feedback reference accuracy
■Wide bandwidth error amplifier
■Single resistor oscillator frequency tting
■Oscillator synchronization capability
■Programmable soft-start
msi是什么
■High voltage, low dropout bias regulator
浙江理工大学分数线■Thermal shutdown protection
Package
■TSSOP-16EP
Simplified Application Schematic
30083901
© 2009 National Semiconductor LM5088 Wide Input Range Non-Synchronous Buck Controller
Connection Diagrams
30083902
Top View (Dither version)
LM5088-1
30083903
Top View (Restart version)
LM5088-2
Ordering Information
Order Number Description NSC Package Drawing
Supplied As LM5088MH-1TSSOP-16EP, Dithering MXA16A 73 Units in a Rail LM5088MHX-1TSSOP-16EP, Dithering MXA16A 2500 Units on Tape and Reel
LM5088MH-2TSSOP-16EP, Restart MXA16A 73 Units in a Rail LM5088MHX-2
TSSOP-16EP, Restart
MXA16A
2500 Units on Tape and Reel
Pin Descriptions
Pin(S)Name Description Application Information
1VIN Input supply voltage
IC supply voltage. The operating range is 4.5V to 75V
2
EN
Enable input
If the EN pin voltage is below 0.4V the regulator will be in a low power state. If the EN pin voltage is between 0.4V and 1.2V the controller will be in standby mode. If the EN pin voltage is above 1.2V the controller will be operational. An external voltage divider can be ud to t a line under voltage
shutdown threshold. If the EN pin is left open, a 5µA pull-up current forces the pin to the high state and enables the controller.
3SS Soft-start
When SS is below the internal 1.2V reference, the SS voltage will control the error amplifier. An internal 11 µA current source charges an external capacitor to t the start-up rate of the controller. The SS pin is held low in the standby,VCC UV and thermal shutdown states. The SS pin can be ud for voltage tracking by connecting this pin to a master voltage supply less than 1.2V. The applied voltage will act as the reference for the error amplifier.
4RAMP Ramp control signal
An external capacitor connected between this pin and the GND pin ts the ramp slope ud for emulated current mode control. Recommended capacitor range 100 pF to 2000 pF. See the Applications ction for lection of capacitor value.
2
L M 5088
Pin(S)Name Description Application Information
5RT/SYNC Internal oscillator frequency
t input and
synchronization input The internal oscillator is programmed with a single resistor between this pin and the GND pin. The recommended frequency range is 50 kHz to 1 MHz. An external synchronization signal, which is higher in frequency than the programmed frequency, can be applied to this pin through a small coupling capacitor. The RT resistor to ground is required even when using external synchronization.
6GND Ground Ground return.
7COMP Output of the internal error
amplifier The loop compensation network should be connected between this pin and the FB pin.
hurry8FB Feedback signal from the
regulated output This pin is connected to the inverting input of the internal error amplifier. The regulation threshold is 1.205V.
9OUT Output voltage connection Connect directly to the regulated output voltage.
10DITH Frequency Dithering
( LM5088-1 Only)A capacitor connected between DITH pin and GND is charged and discharged by 27 µA current sources. As the voltage on the DITH pin ramps up and down, the oscillator frequency is modulated between -5% to +5% of the nominal frequency t by the RT resistor. Grounding the DITH pin will disable the frequency dithering mode.
10RES Hiccup Mode Restart
( LM5088-2 Only)The RES pin is normally connected to an external capacitor that ts the timing for hiccup mode current limiting. In normal operation, a 25µA current source discharges the RES pin capacitor to ground. If cycle-by-cycle current limit threshold is exceeded during any PWM cycle, the current sink is disabled and RES capacitor is charged by an internal 50 µA current. If the RES voltage reaches 1.2V, the HG pin gate drive signal will be disabled and the RES pin capacitor will be discharged by a 1 µA current sink. Normal operation will resume when the RES pin falls below 0.2V.
11CSG Current Sen Ground Low side reference for the current n resistor.
12CS Current n Current measurement connection for the re-circulating diode. An external
n resistor and an internal sample/hold circuit n the diode current at
the conclusion of the buck switch off-time. This current measurement providesothers是什么意思
the DC offt level for the emulated current ramp.
13SW Switching node Connect to the source terminal of the external MOSFET switch.
14HG High Gate Connect to the gate terminal of the external MOSFET switch.
15BOOT Input for bootstrap capacitor An external capacitor is required between the BOOT and the SW pins to provide
bias to the MOSFET gate driver. The capacitor is charged from VCC via an
internal diode during the off-time of the buck switch.
when you belive16VCC Output of the bias regulator VCC tracks VIN up to the regulation level (7.8V Typ). A 0.1 µF to 10 µF ceramic
decoupling capacitor is required. An external voltage between 8.3V and 13V
can be applied to this pin to reduce internal power dissipation.
LM5088
Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required,plea contact the National Semiconductor Sales Office/Distributors for availability and specifications.VIN, VOUT to GND 76V BOOT to GND 90V SW to GND -2V to 76V VCC to GND -0.3V to 16V HG to SW -0.3V to BOOT
+0.3V EN to GND 14V
BOOT to SW
-
0.3V to 16V
CS, CSG to GND
-0.3V to 0.3V All other inputs to GND -0.3V to 7V
ESD Rating
Human Body Model
2 kV
Storage Temperature Range −65°C to + 150°C
Junction Temperature + 150°C
Operating Ratings
(Note 1)
VIN Voltage
4.5V to 75V VCC Voltage (externally supplied)8.3V to 13V Operation Junction Temperature
−40°C to + 125°C
Electrical Characteristics
Limits in standard type are for T J = 25°C only; limits in boldface type apply over the
junction temperature (T J ) range of -40°C to +125°C . Minimum and Maximum limits are guaranteed through test, design, or statistical correlation. Typical values reprent at T J = 25°C, and are provided for reference purpos only. Unless otherwi stated the following conditions apply: V VIN = 48V, V VCC = 8V, V EN = 5V R RT = 31.6 k Ω, No load on HG. See Note 4.Symbol Parameter
Conditions
Min
Typ
Max
Units
VIN SUPPLY
I BIAS VIN Operating Current V FB = 1.3V 3.8 5.5mA I STANDBY VIN Standby Current V EN = 1V 2.9 3.6mA I SHUTDOWN VIN Shutdown Current V EN = 0V 1526µA VCC REGULATOR
V VCC(Reg)VCC Regulation V VCC = open
7.47.88.2V V VCC(Reg)
VCC Regulation
V VIN = 4.5V,VVCC=open 4.3 4.5V VCC Sourcing Current Limit V VCC = 03035 mA V VCC(UV)
VCC Under-Voltage Lockout Threshold Positive going VVCC
3.74
4.2V VCC Under-Voltage Hysteresis
200 mV ENABLE THRESHOLDS
EN Shutdown Threshold V EN Rising 320400480mV EN Shutdown Hysteresis V EN Falling 100 mV EN Standby Threshold V EN Rising 1.1 1.2 1.3V EN Standby Hysteresis V EN Falling 120 mV
EN Pull-up Current Source
V EN = 0V
5
µA
SOFT- STAR T
SS Pull-up Current Source V SS = 0V 81113µA FB to SS Offt V FB = 1.3V
150 mV ERROR AMPLIFIER
V REF FB Reference Voltage Measured at FB Pin FB = COMP 1.187 1.205 1.223V FB Input Bia
s Current V FB = 1.2V 18100nA COMP Sink/Source Current 3 mA AOL DC Gain
60 dB FBW Unity gain bandwidth 3 MHz PWM COMPARATORS
T HG(OFF)Forced HG Off-time
185280365ns T ON(MIN)
Minimum HG On-time
V VIN = 60V 55 ns
COMP to PWM comparator offt
930
mV
4
L M 5088
Symbol Parameter Conditions Min Typ Max Units OSCILLATOR (RT Pin)
LM5088-2 (Non-Dithering)
F
nom1Nominal Oscillator Frequency R
RT
= 31.6 kΩ180200220kHz
F
nom2R
RT
= 11.3 kΩ430500565kHz LM5088-1 (Dithering)
F min Dithering Range Minimum Dither Frequency F
nom
-5%kHz
F max Maximum Dither Frequency F
nom
+5%kHz
SYNC
SYNC positive threshold 2.3V
SYNC Pul Width15150ns CURRENT LIMIT
V
CS(TH)Cycle by cycle n voltage threshold V
RAMP
= 0V112120136mV
Cycle by Cycle Current Limit Delay V
RAMP
= 2.5V280ns Buck Switch VDS protection VIN to SW 1.5V
CURRENT LIMIT RESTART (RES Pin)
V resup RES Threshold Upper (rising)V
CS
= 0.125 1.1 1.2 1.3V
V
resdown
RES Threshold Lower (falling)0.10.20.3V
I charge Charge source current V
CS
>= 0.125405065µA
I discharge Discharge sink current V
CS
< 0.125202734µA
东安格利亚大学
I
rampdown
Discharge sink current -(post fault)0.8 1.2 1.6µA RAMP GENERATOR日堙月塞
I
RAMP1RAMP Current 1V
VIN
= 60V, V
OUT
= 10V235295345µA
I
RAMP2RAMP Current 2V
VIN
= 10V, V
OUT
= 10V182530µA
VOUT Bias Current V
OUT
= 48V250µA
RAMP Output Low Voltage V
micheVIN
= 60V, V
OUT
= 10V200mV
HIGH SIDE (HG) GATE DRIVER
V OLH HG Low-state Output Voltage I
HG
= 100 mA115215mV
V OHH HG High-state Output Voltage I
HG
= -100 mA, V
OHH
= V
BOOT
- V
HG
240mV
HG Ri Time C
load
= 1000 pF12ns
HG Fall Time C
loadopacity
= 1000 pF6ns
I OHH Peak HG Source Current V
HG
= 0V 1.5A
I OLH Peak HG Sink Current V
HG
= V
VCC
中间
2A BOOT UVLO BOOT to SW3V
Pre R
DS(ON)Pre-Charge Switch ON- resistance I
VCC
= 1 mA72ΩPre-Charge switch ON time300ns
THERMAL
T
SD
Thermal Shutdown Temperature Junction Temperature Rising165°C
Thermal Shutdown Hysterisis Junction Temperature Falling25°C θJC Thermal Resistance Junction to Ca6°C /W θJA Thermal Resistance Junction to Ambient40°C /W
Note 1:Absolute Maximum Ratings are limits beyond which damage to the device may occur. Operating Ratings are conditions under which operation of the device is intended to be functional. For guaranteed specifications and test conditions, e the Electrical Characteristics.
Note 2:The human body model is a 100 pF capacitor discharged through a 1.5 kΩ resistor into each pin.
Note 3:RAMP and COMP are output pins. As such they are not specified to have an external voltage applied.
Note 4:Typical specifications reprent the most likely parametric norm at 25°C operation.
Note 5:For detailed information on soldering plastic MSOP packages refer to the Packaging Data Book available from National Semiconductor Corporation.
LM5088
