LM51551

Nonsynchronous Boost/SEPIC/Flyback Controller

The LM51551 is a nonsynchronous boost/sepic/flyback controller from Texas Instruments. View the full LM51551 datasheet below including key specifications, electrical characteristics, absolute maximum ratings.

LM51551 shares its datasheet with LM5155, whose page lists every part number it covers.

Official LM51551 datasheet (PDF) — the source this page was extracted from.

Manufacturer

Texas Instruments

LM51551 Key Specifications

Parameter	Value
Hiccup Mode	Enabled (64 cycles enable, 8 cycles reset)
Minimum On-Time	50 ns
Maximum Duty Cycle	85% typ at 2.2 MHz; 93% typ at 100 kHz
Package Dimensions	3.00 mm × 2.00 mm
Switching Frequency	100 kHz to 2.2 MHz (programmable)
Shutdown Current (IQ)	≤ 2.6 µA
Operating Current (IQ)	≤ 480 µA
Current Limit Threshold	100 mV ±7%
Feedback Reference Voltage	1V ±1%
Input Transient Protection	up to 50V
MOSFET Driver Peak Current	1.5A
Thermal Shutdown Threshold	175°C (15°C hysteresis)
Minimum Boost Supply Voltage	1.5V when BIAS ≥ 3.5V
Input Operating Voltage Range	3.5V to 45V (2.97V to 16V when BIAS = VCC)
Error Amplifier Transconductance	2 mA/V

LM51551 Overview

Part: LM5155 / LM51551 (LM5155x), Texas Instruments

Type: Nonsynchronous Boost, SEPIC and Flyback Controller (peak current mode)

Description: 3.5–45 V operating input (2.97–16 V when BIAS = VCC) nonsynchronous boost/SEPIC/flyback controller with up to 2.2 MHz switching frequency, 1.5 A peak gate driver and ±1% feedback reference.

Operating Conditions:

BIAS supply voltage: 2.97–45 V
VCC voltage: 2.97–16 V
Operating junction temperature: -40 to 125 °C
Switching frequency: 100 kHz to 2200 kHz

Absolute Maximum Ratings:

BIAS to AGND: -0.3 to 50 V
VCC to AGND: -0.3 to 18 V (or VBIAS + 0.3 V, whichever is lower)
PGOOD to AGND: -0.3 to 18 V
Junction temperature: -40 to 150 °C
Storage temperature: -55 to 150 °C

Key Specs:

Shutdown current (VBIAS = 12 V, VUVLO = 0 V): 2.6 μA typ, 5 μA max
Operating current (VBIAS = 12 V, VUVLO = 2 V, RT = 220 kΩ): 480 μA typ, 540 μA max
VCC regulation (VBIAS = 8 V, no load): 6.5–7 V (6.85 V typ)
VCC UVLO rising threshold: 2.75–2.95 V (2.85 V typ)
VCC sourcing current limit (VBIAS = 10 V, VCC = 0 V): 35 mA min, 105 mA typ
UVLO rising threshold: 1.425–1.575 V (1.5 V typ); hysteresis current 5 μA typ
Enable rising threshold: 0.4–0.7 V (0.52 V typ)
Soft-start current: 9–11 μA (10 μA typ)
Thermal resistance RθJA: 63.7 °C/W (40.8 °C/W on LM5155EVM-BST)

Features:

Input transient protection up to 50 V
Minimum boost supply voltage of 1.5 V when BIAS ≥ 3.5 V
Integrated error amplifier allows primary-side regulation without an optocoupler (flyback)
100 mV ±7% low current limit threshold, constant peak current limiting over input voltage
1.5 A peak MOSFET driver; supports external VCC supply
Dynamically programmable switching frequency, optional clock synchronization
Optional hiccup mode short-circuit protection (LM51551 enabled, LM5155 disabled)
Programmable line UVLO, OVP, thermal shutdown
±1% feedback reference (1 V)
Programmable slope compensation, adjustable soft start, PGOOD indicator
Functional Safety-Capable

Applications:

Multiple-output flyback without optocoupler
LED bias supply
Wide input boost, SEPIC, flyback power module
Portable speaker
Battery-powered boost, SEPIC, flyback

Package:

WSON-12 (DSS), 3.00 mm × 2.00 mm

LM51551 Features

Functional Safety-Capable
-Documentation available to aid functional safety system design
Wide input operating range for battery applications
-3.5-V to 45-V operating range
-2.97-V to 16-V when BIAS = VCC
-Minimum boost supply voltage 1.5 V when BIAS ≥ 3.5 V
-Input transient protection up to 50 V
Minimized battery drain
-Low shutdown current (IQ ≤ 2.6 μA)
-Low operating current (I Q ≤ 480 μA)
Small solution size and low cost
-Maximum switching frequency of 2.2 MHz
-12-Pin WSON package (3 mm × 2 mm)
-Integrated error amplifier allows primary-side regulation without optocoupler (flyback)
-Minimized undershoot during cranking (startstop application)
Higher efficiency with low-power dissipation
-100-mV ±7% Low current limit threshold
-Strong 1.5-A peak standard MOSFET driver
-Supports external VCC supply
Avoid AM band interference and crosstalk
-Optional clock synchronization
-Dynamically programmable switching frequency from 100 kHz to 2.2 MHz
Integrated protection features
-Constant peak current limiting over input voltage
-Optional hiccup mode short-circuit protection (see the Device Comparison Table )

Typical Boost Application

Product Folder Links:

LM5155

LM51551

-Programmable line UVLO
-OVP protection
-Thermal shutdown
Accurate ±1% accuracy feedback reference
Programmable extra slope compensation
Adjustable soft start
PGOOD indicator
Create a custom design using the LM5155x with the WEBENCH ® power designer

LM51551 Applications

LM51551 Pin Configuration

Figure 7-1. 12-Pin WSON DSS Package (Top View)

Table 7-1. Pin Functions

PIN - NO.	PIN - NAME	TYPE (1)	DESCRIPTION
1	BIAS	P	Supply voltage input to the VCC regulator. Connect a bypass capacitor from this pin to PGND.
2	VCC	P	Output of the internal VCC regulator and supply voltage input of the MOSFET driver. Connect a ceramic bypass capacitor from this pin to PGND.
3	GATE	O	N-channel MOSFET gate drive output. Connect directly to the gate of the N-channel MOSFET through a short, low inductance path.
4	PGND	G	Power ground pin. Connect directly to the ground connection of the sense resistor through a low inductance wide and short path.
5	CS	I	Current sense input pin. Connect to the positive side of the current sense resistor through a short path.
6	COMP	O	Output of the internal transconductance error amplifier. Connect the loop compensation components between this pin and PGND.
7	AGND	G	Analog ground pin. Connect to the analog ground plane through a wide and short path.
8	FB	I	Inverting input of the error amplifier. Connect a voltage divider from the output to this pin to set output voltage in boost/SEPIC topologies. Connect the low-side feedback resistor to AGND.
9	SS	I	Soft-start time programming pin. An external capacitor and an internal current source set the ramp rate of the internal error amplifier reference during soft start. Connect the ground connection of the capacitor to AGND.
10	RT	I	Switching frequency setting pin. The switching frequency is programmed by a single resistor between RT and AGND.
11	PGOOD	O	Power-good indicator. An open-drain output which goes low if FB is below the under voltage threshold. Connect a pullup resistor to the system voltage rail.
12	UVLO/EN/ SYNC	I	Undervoltage lockout programming pin. The converter start-up and shutdown levels can be programmed by connecting this pin to the supply voltage through a resistor divider. The internal clock can be synchronized to an external clock by applying a negative pulse signal into the UVLO/EN/ SYNC pin. This pin must not be left floating. Connect to BIAS pin if not used. Connect the low-side UVLO resistor to AGND.
-	EP	-	Exposed pad of the package. The exposed pad must be connected to AGND and the large ground copper plane to decrease thermal resistance.

(1) G = Ground, I = Input, O = Output, P = Power

Table 7-1. Pin Functions

LM51551 Electrical Characteristics

Typical values correspond to TJ = 25°C. Minimum and maximum limits apply over TJ = -40°C to 125°C. Unless otherwise stated, V BIAS = 12 V, RT = 9.09 kΩ

PARAMETER	PARAMETER	TEST CONDITIONS	MIN	TYP	MAX	UNIT
SUPPLY CURRENT	SUPPLY CURRENT	SUPPLY CURRENT	SUPPLY CURRENT	SUPPLY CURRENT	SUPPLY CURRENT	SUPPLY CURRENT
I SHUTDOWN(BIAS)	BIAS shutdown current	V BIAS = 12 V, V UVLO = 0 V		2.6	5	μA
I OPERATING(BIAS)	BIAS operating current	V BIAS = 12 V, V UVLO = 2 V, V FB = V REF , R T = 220 kΩ		480	540	μA
VCC REGULATOR	VCC REGULATOR	VCC REGULATOR	VCC REGULATOR	VCC REGULATOR	VCC REGULATOR	VCC REGULATOR
V VCC-REG	VCC regulation	V BIAS = 8 V, No load	6.5	6.85	7	V
	VCC regulation	V BIAS = 8 V, I VCC = 35 mA	6.5			V
V VCC-UVLO(RISING)	VCC UVLO threshold	VCC rising	2.75	2.85	2.95	V
	VCC UVLO hysteresis	VCC falling		0.063		V
I VCC-CL	VCC sourcing current limit	V BIAS = 10 V, V VCC = 0 V	35	105		mA
ENABLE	ENABLE	ENABLE	ENABLE	ENABLE	ENABLE	ENABLE
V EN(RISING)	Enable threshold	EN rising	0.4	0.52	0.7	V

Typical values correspond to TJ = 25°C. Minimum and maximum limits apply over TJ = -40°C to 125°C. Unless otherwise stated, V BIAS = 12 V, RT = 9.09 kΩ

	PARAMETER	TEST CONDITIONS	MIN	TYP	MAX	UNIT
V EN(FALLING)	Enable threshold	EN falling	0.33	0.49	0.63	V
V EN(HYS)	Enable hysteresis	EN falling		0.03		V
UVLO/SYNC
V UVLO(RISING)	UVLO / SYNC threshold	UVLO rising	1.425	1.5	1.575	V
V UVLO(FALLING)	UVLO / SYNC threshold	UVLO falling	1.370	1.45	1.520	V
V UVLO(HYS)	UVLO / SYNC threshold hysteresis	UVLO falling		0.05		V
I UVLO	UVLO hysteresis current	V UVLO = 1.6 V	4	5	6	μA
SS
I SS	Soft-start current SS pull-down switch R DSON		9	10 55	11	μA Ω
PULSE WIDTH	MODULATION
fsw1	Switching frequency	R T = 220 kΩ	85	100	115	kHz
fsw2	Switching frequency	R T = 9.09 kΩ	1980	2200	2420	kHz
t ON(MIN)	Minimum on-time	R T = 9.09 kΩ		50		ns
D MAX1	Maximum duty cycle limit	R T = 9.09 kΩ	80%	85%	90%
D MAX2	Maximum duty cycle limit	R T = 220 kΩ	90%	93%	96%
CURRENT SENSE
I SLOPE	Peak slope compensation current	R T = 220 kΩ	22.5	30	37.5	μA
V CLTH	Current Limit threshold (CS- PGND)		93	100	107	mV
HICCUP MODE PROTECTION (LM51551)	HICCUP MODE PROTECTION (LM51551) Hiccup enable cycles Hiccup timer reset cycles			64 8		Cycles Cycles
ERROR AMPLIFIER
V REF	FB reference	LM5155, LM51551	0.99	1	1.01	V
Gm	Transconductance			2		mA/V
	COMP sourcing current	V COMP = 1.2 V	180			μA
	COMP clamp voltage	COMP rising (V UVLO = 2.0V)	2.5	2.8		V
	COMP clamp voltage	COMP falling		1	1.1	V
OVP
V OVTH	Over-voltage threshold Over-voltage threshold	FB rising (referece to V REF ) FB falling (referece to V REF )	107%	110% 105%	113%
PGOOD
	PGOOD pull-down switch R DSON	1 mA sinking		90		Ω
V UVTH	Undervoltage threshold Undervoltage threshold	FB falling (referece to V REF ) FB rising (referece to V REF )	87%	90% 95%	93%
MOSFET DRIVER
	High-state voltage drop	100 mA sinking		0.25		V
	Low-state voltage drop	100 mA sourcing		0.15		V
THERMAL SHUTDOWN	THERMAL SHUTDOWN
T TSD	Thermal shutdown threshold Thermal shutdown hysteresis	Temperature rising		175 15		°C °C

LM51551 Absolute Maximum Ratings

Over the recommended operating junction temperature range (1)

		MIN	MAX	UNIT
Input	BIAS to AGND	-0.3	50	V
Input	UVLO to AGND	-0.3	V BIAS +0.3	V
Input	SS to AGND (2)	-0.3	3.8	V
Input	RT to AGND (2)	-0.3	3.8	V
Input	FB to AGND	-0.3	3.8	V
Input	CS to AGND(DC)	-0.3	0.3	V
Input	CS to AGND(100ns transient)	-1		V
Input	CS to AGND(20ns transient)	-2		V
Input	PGND to AGND	-0.3	0.3	V
	VCC to AGND	-0.3	18 (3)	V
	GATE to AGND (100ns transient)	-1		V
	GATE to AGND (50ns transient)	-2		V
	PGOOD to AGND (4)	-0.3	18	V
	COMP to AGND (5)	-0.3		V
Junction temperature, T J (6)	Junction temperature, T J (6)	-40	150	°C
Storage temperature, T stg	Storage temperature, T stg	-55	150	°C

(2) This pin is not specified to have an external voltage applied.
(3) 18 V or VBIAS + 0.3 V whichever is lower
(4) The maximum current sink is limited to 1 mA when VPGOOD>VBIAS.
(5) This pin has an internal max voltage clamp which can handle up to 1.6 mA.
(6) High junction temperatures degrade operating lifetimes. Operating lifetime is de-rated for junction temperatures greater than 125°C.

LM51551 Recommended Operating Conditions

Over the recommended operating junction temperature range of -40°C to 125°C (unless otherwise specified) (1)

		MIN	MAX	UNIT
V BIAS	Bias input (2)	2.97	45	V
V VCC	VCC voltage (3)	2.97	16	V
V UVLO	UVLO input	0	45	V
V FB	FB input	0	3.7	V
f SW	Typical switching frequency	100	2200	kHz
f SYNC	Synchronization pulse frequency	100	2200	kHz
T J	Operating junction temperature	-40	125	°C

LM51551 Thermal Information

	THERMAL METRIC (1)	LM5155x DSS(WSON) 12 PINS	UNIT
R θJA	Junction-to-ambient thermal resistance (LM5155EVM-BST)	40.8	°C/W
R θJA	Junction-to-ambient thermal resistance	63.7	°C/W
R θJC(top)	Junction-to-case (top) thermal resistance	61.0	°C/W
R θJB	Junction-to-board thermal resistance	32.1	°C/W
ψ JT	Junction-to-top characterization parameter (LM5155EVM-BST)	1.5	°C/W
ψ JT	Junction-to-top characterization parameter	2.3	°C/W
ψ JB	Junction-to-board characterization parameter (LM5155EVM-BST)	22.5	°C/W
ψ JB	Junction-to-board characterization parameter	31.9	°C/W
R θJC(bot)	Junction-to-case (bottom) thermal resistance	11.2	°C/W

LM51551 Typical Application

See the How to Design a Boost Converter Using LM5155-Q1 application note for information on loop response and component selections for the boost converter.

Variants on the same datasheet

These parts have exact links to the same datasheet. They are candidates to compare, not verified drop-in replacements; check package, pinout and electrical limits.

Part Number	Manufacturer	Package
LM5155	Texas Instruments	WSON-12 3.0x2.0mm
LM5155-Q1	Texas Instruments	WSON-12 3.0x2.0mm
LM51551-Q1	Texas Instruments	WSON-12 3x2mm
LM51551DSSR	Texas Instruments	WSON-12 3.0x2.0mm
LM51551DSST	Texas Instruments	WSON-12 3.0x2.0mm
LM5155DSSR	Texas Instruments	12-WFDFN Exposed Pad
LM5155DSST	Texas Instruments	WSON-12 3x2mm

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