LINEAR TECHNOLOGY LT1619 Technical data

FEATURES

LT1619

Low Voltage Current Mode

PWM Controller

U

DESCRIPTIO

■

Wide VIN Range: 1.9V to 18V

■

300kHz Fixed Frequency Current Mode Control

■

1A Rail-to-Rail N-Channel MOSFET Driver

■

Low 53mV Current Limit Threshold Voltage
Improves Efficiency

■

Implements Boost, SEPIC and Flyback Converters
Requiring Low Side Power Transistors

■

Internal Current Sense Amplifier
with Leading Edge Blanking

■

Up to 500kHz External Synchronization

■

Burst Mode® Operation for High Efficiency
at Light Load

■

140µA Quiescent Current

■

15µA Shutdown Current

■

8-Lead MSOP and SO Packages

U

APPLICATIO S

■

3.3V to 5V DC/DC Converters

■

Distributed Power Supplies

■

Isolated Power Supplies

The LT®1619 is a fixed frequency PWM controller for
implementing current mode DC/DC converters with mini­mum external parts. The LT1619 operates with input
voltages ranging from 1.9V to 18V and is suitable for a
variety of battery-powered and distributed DC/DC con­verters. The internal rail-to-rail N-channel MOSFET driver
operates either from the input in the nonbootstrapped
mode or from the output in bootstrapped operation. The
driver is designed to drive a low side power transistor in
boost, SEPIC, flyback and other topologies.

Converter efficiency is improved at heavy loads with a
53mV current sense voltage and at light load with Burst
Mode operation. The operating frequency is internally set
at 300kHz. The oscillator can also be synchronized exter­nally up to 500kHz. No load quiescent current is 140µA and
shutdown current is 15µA.

The LT1619 is available in 8-lead MSOP and SO packages.

, LTC and LT are registered trademarks of Linear Technology Corporation.

Burst Mode is a registered trademark of Linear Technology Corporation.

TYPICAL APPLICATIO

37.4k

12.4k

220pF

C1: PANASONIC EEFCDOK220R

: KEMET T495X227K010AS (×2)

C

OUT

D1: MBRD835L
L1: COILCRAFT DO5022P-562

75k

15nF

Figure 1. High Efficiency 3.3V to 5V DC/DC Converter

1

S/S

2

FB

LT1619

3

V

C

4

GND

V

DRV

GATE

SENSE

8

IN

7

6

5

U

0.1µF

V

IN

3.3V

+

C1
22µF

0.1µF

L1

5.6µH
5A

M1
Si9804

R

SENSE

0.01Ω

D1

1619 F01

V

OUT

5V

2.2A

+

C

OUT

440µF

95

90

85

80

EFFICIENCY (%)

75

70

1 100 1000

Efficiency

10
LOAD CURRENT (mA)

1619 F01a

1619fa

1

LT1619

1

2

3

4

8

7

6

5

TOP VIEW

V

IN

DRV
GATE
SENSE

S/S

FB
V

C

GND

S8 PACKAGE

8-LEAD PLASTIC SO

WWWU

ABSOLUTE AXI U RATI GS

(Note 1)

Input Voltage (VIN) ................................... –0.3V to 20V

Gate Drive Supply Voltage (DRV) ............. –0.3V to 20V

Shutdown/Synch Voltage (S/S) ................ –0.3V to 20V

Feedback Voltage (FB) .............................................. V

IN

Compensation Voltage (VC) ...................................... 3V

Gate Drive Output Current (GATE) ........................ ±1.5A

UU

W

PACKAGE/ORDER I FOR ATIO

ORDER PART

NUMBER

TOP VIEW

S/S

1

FB

2

V

3

C

4

GND

MS8 PACKAGE

8-LEAD PLASTIC MSOP

T

= 125°C, θJA = 200°C/W

JMAX

8
7
6
5

V

IN

DRV
GATE
SENSE

LT1619EMS8

MS8 PART MARKING

LTHC

Current Sense Voltage (SENSE) .................– 0.5V to V

IN

Operating Temperature Range (Note 2) .. –40°C to 85°C

Junction Temperature (Note 3)............................. 125°C

Storage Temperature Range ................. –65°C to 150°C

Lead Temperature (Soldering, 10 sec)..................300°C

ORDER PART

NUMBER

LT1619ES8

S8 PART MARKING

1619

= 125°C, θJA = 120°C/W

T

JMAX

Consult LTC Marketing for parts specified with wider operating temperature ranges.

ELECTRICAL CHARACTERISTICS

The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C.
V

= V

IN

PARAMETER CONDITIONS MIN TYP MAX UNITS

Reference Voltage Measured at the FB Pin ● 1.22 1.24 1.26 V
Reference Line Regulation 1.9V ≤ VIN ≤ 18V 0.004 0.05 %/V
FB Input Bias Current VFB = V
Error Amplifier Transconductance 80 170 260 µΩ
Error Amplifier Output Source Current VFB = 1V, V
Error Amplifier Output Sink Current VFB = 1.5V, V
Error Amplifier Clamp Voltage VFB = 1V 1.6 2.2 V
Undervoltage Lockout Threshold 1.65 1.85 V
Input Voltage Range ● 1.9 18 V
Switching Frequency 1.9V ≤ VIN ≤ 18V ● 220 300 360 kHz
Synchronization Frequency Range 370 500 kHz
Maximum Duty Cycle ● 88 92 %
Current Limit Threshold ● 40 53 66 mV
Burst Mode Operation Current Limit 10 mV

2

= 2.5V, V

DRV

= VIN, COMP open, V

S/S

= 0V unless otherwise noted.

SENSE

REF

= 1V 4 8.7 14 µA

COMP

= 1V 4 8.7 14 µA

COMP

10 25 nA

–1

1619fa

LT1619

ELECTRICAL CHARACTERISTICS

The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C.
V

= V

IN

= 2.5V, V

DRV

PARAMETER CONDITIONS MIN TYP MAX UNITS

Current Sense Input Current V
Current Limit Delay 150 ns
Driver Output Rise Time CL = 3300pF 30 ns
Driver Output Fall Time CL = 3300pF 35 ns
Driver Output High Level I

Driver Output Low Level I

Shutdown Driver Output Level V
Idle Mode Driver Output Level V
S/S Pin Current V

Operating Supply Current VFB = 1V 9 mA
Quiescent Supply Current V
Shutdown Supply Current V

Shutdown Threshold 0.45 1.2 V
Shutdown Delay 12 17 33 µs

= VIN, COMP open, V

S/S

= 0V unless otherwise noted.

SENSE

= 0V ● –90 –120 –150 µA

SENSE

= –20mA V

OUT

I

= –200mA V

OUT

= 20mA 100 200 mV

OUT

= 200mA 0.5 0.7 V

I

OUT

= 0V, I

S/S

= VIN, VFB = 1.5V, I

S/S

= V

S/S

= 0V –2 µA

V

S/S

= VIN, VFB = 1.5V ● 140 220 µA

S/S

= 0V 15 19 µA

S/S

= 0V, VIN = 18V, TA = 85°C40µA

V

S/S

= 20mA 100 200 mV

OUT

= 20mA 100 200 mV

OUT

IN

– 0.6 V

DRV

– 1.6 V

DRV

– 0.35 V

DRV

– 1.2 V

DRV

4 µA

Note 1: Absolute Maximum Ratings are those values beyond which the life
of the device may be impaired.

Note 2: The LT1619E is guaranteed to meet performance specifications
from 0°C to 70°C. Specifications over the –40°C to 85°C operating

Note 3: T
dissipation P
the formula:

is calculated from the ambient temperature TA, the power

J

T

= TA + PD • θ

J

temperature range are assured by design, characterization and correlation
with statistical process controls.

UW

TYPICAL PERFOR A CE CHARACTERISTICS

Bandgap Voltage vs Temperature I

1.245
VIN = 2.5V

1.243

1.241

1.239

1.237

1.235

1.233

1.231

BANDGAP VOLTAGE (V)

1.229

1.227

1.225

–20 0 20 40 60 120

–40

TEMPERATURE (°C)

80 100

1619 G01

(µA)
I

S/S

vs V

S/S

S/S

5

4

3

2

1

0

–1

–2

–3

1.0 2.0 3.0 5.03.50.5 1.5 2.5 4.5

0

TA = –40°C

TA = 25°C

TA = 85°C

V

(V)

S/S

4.0

and the thermal resistance θJA of the package according to

D

JA

S/S Pin Current vs Temperature

5

1619 G02

4

3

2

1

0

S/S PIN CURRENT (µA)

–1

–2

–3

–20

–40

V

= 2.5V

S/S

V

= 0V

S/S

0

40

20

TEMPERATURE (°C)

60

80

100

1619 G03

120

1619fa

3

LT1619

TEMPERATURE (°C)

–40

CURRENT LIMIT THRESHOLD (mV)

57

20

1619 G09

54

52

–20 0 40

51

50

58

56

55

53

60 80 100

VIN = 2.5V

UW

TYPICAL PERFOR A CE CHARACTERISTICS

Shutdown Supply Current
vs Input Voltage

45

40

35

30

25

20

SUPPLY CURRENT (µA)

15

10

5

0

TA = –40°C

TA = 25°C

4 8 12 20142 6 10 18

INPUT VOLTAGE (V)

Maximum Duty Ratio
vs Temperature

95

VIN = 2.5V

94

93

92

DUTY RATIO (%)

91

TA = 85°C

Idle Mode Supply Current
vs Temperature

200

VIN = 2.5V

190

180

170

160

150

IDLE MODE SUPPLY CURRENT (µA)

140

–40

–20 20

16

1619 G04

040

TEMPERATURE (°C)

60

80

100

120

1619 G05

Deviation from Nominal
Frequency vs Input Voltage

8

TA = 25°C
NOMINAL FREQUENCY = 300kHZ

6

4

2

0

FREQUENCY DEVIATION (%)

–2

Frequency Deviation from
Nominal vs Temperature

10

VIN = 2.5V

8

NOMINAL FREQUENCY = 300kHz
6
4
2

0

–2

–4
–6

–8

DEVIATION FROM NOMINAL FREQUENCY (%)

–10

–20 0 40

–40

20

TEMPERATURE (°C)

60 80 100

Current Limit Threshold
vs Temperature

1619 G06

90

–40 –20

Burst Mode Operation Current
Limit Threshold vs Temperature

14

VIN = 2.5V
DUTY CYCLE = 0

12

10

8

6

4

2

CURRENT LIMIT THRESHOLD (mV)

0

–40

–20 0

4

40

20

0

TEMPERATURE (°C)

40 80 100

20 60

TEMPERATURE (°C)

80

100

1619 G07

1619 G10

60

–4

4

2

0

10

8

6

INPUT VOLTAGE (V)

SENSE Pin Input Bias Current
vs Temperature

–115

V

= 0V

SENSE

–117
–119
–121
–123
–125
–127
–129

SENSE PIN CURRENT (µA)

–131
–133
–135

–40

–20

0

20

TEMPERATURE (°C)

16

12

14

18

1619 G08

20

SENSE Pin Input Bias Current
vs Sense Voltage

–90

TA = 25°C

–95

–100

–105

–110

–115

–120

SENSE PIN CURRENT (µA)

–125

40

60

80

100

1619 G11

–130

–10

010

20 30

V

SENSE

(mV)

40 50

60

1619 G12

1619fa

LT1619

U

UU

PI FU CTIO S

S/S (Pin 1): Shutdown and Synchronization. Shutdown is
active low with a typical threshold voltage of 0.9V. For
normal operation, the S/S pin is tied to VIN. To externally
synchronize the controller, drive the S/S pin with pulses.

FB (Pin 2): The inverting Input of the Error Amplifier.
Connect the resistor divider tap here. Set V
to V

= 1.24(1 + R1/R2). See Figure 1.

OUT

according

OUT

VC (Pin 3): Compensation Pin for the Error Amplifier. VC is
the output of the transconductance amplifier. Overall loop
is compensated with an RC network from this pin to the
ground.

GND (Pin 4): Ground. Connect to local ground plane.

W

BLOCK DIAGRA

V

CVIN

1.24V

FB

3 8

ERROR

AMPLIFIER

1.8V

+

g

m

2

–

–

A2

UVLO

+

–

A1

V

+

B

–

SENSE (Pin 5): The Input of the Current Sense Amplifier.
The SENSE pin is connected to the source of the N-channel
MOSFET and to a sense resistor to the ground. The current
limit threshold is internally set at 53mV, giving a maximum
switch current of 53mV/R

SENSE

.

GATE (Pin 6): The Output of the MOSFET Driver.
DRV (Pin 7): The Pull-Up Supply of the MOSFET Driver. Tie

this pin to VIN (Pin 8) for nonbootstrapped operation or to
the converter output for bootstrapped operation.

VIN (Pin 8): Supply or Battery Input. Must be closely
bypassed to the ground plane.

IDLE

V

IN

DRV

7

S/S

C1

+

++

Σ

RAMP COMP

DELAY

300kHz

OSCILLATOR

REF/BIAS

1

SYNC

SHUTDOWN

CLK

COMPARATOR

CURRENT

LIMIT

S

Q

R

DRIVER

–

CURRENT

SENSE

+

AMP

+

I

–

LIM

280ns

LEADING

EDGE

BLANKING

6

5

4

GATE

SENSE

GND

1619 F02

R

LOAD

SENSE

Figure 2. LT1619 Block Diagram

1619fa

5

LT1619

OPERATIO

U

The LT1619 is a fixed frequency current mode switching
regulator PWM controller that can be used in boost, SEPIC
or flyback modes. The device operates from an input
supply range of 1.9V to 18V, and has a separate supply pin
(DRV) for the gate driver. The DRV pin can be bootstrapped
to V

for additional gate enhancement in low voltage

OUT

applications like 3.3V to 5V boost converters, or con­nected to the input supply for higher voltage inputs.

To best understand operation of the LT1619, please refer
to Figure 2, the Block Diagram. The gate drive circuit turns
on the external MOSFET at the trailing edge of oscillator
output signal CLK. MOSFET current is sensed with an
external resistor (R

of Figure 1). A leading edge

SENSE

blanking circuit disables the current sense amplifier for
280ns immediately following switch turn-on, preventing
gate charging current from prematurely tripping the PWM
comparator. A slope compensating ramp, derived from
the oscillator, is added to the current sense output. The
driver turns off the MOSFET when this sum exceeds the
error amplifier output VC. The switch current is limited
with a separate comparator. The compensating ramp is a
progressive nonlinear function of the operating duty ratio
whereas the current limit does not vary with the duty ratio.

Error amplifier output VC determines the peak switch cur­rent required to regulate the output voltage. VC can be
considered a measure of output current. At heavy loads,
VC is in its upper range. Average and peak inductor cur­rents are high. In this range, the inductor tends to run in
continuous conduction mode (CCM), where current is al­ways flowing in the inductor. As load current decreases,
average and peak inductor current decreases. When the
average inductor current falls below 1/2 of the peak-to-peak
inductor current ripple, the converter enters discontinu­ous conduction mode (DCM), where current in the induc­tor reaches zero sometime during the discharge phase.

Further reduction in output current moves VC towards its
lower operating range, decreasing inductor current. Hys­teretic comparator A1 determines if VC is too low for the
LT1619 to operate efficiently. As VC falls below the trip
voltage VB, A1’s output goes high, turning off all blocks
except the error amplifier, A1 and A2. The LT1619 enters
the idle state and switching stops. The device draws just
140µA from the input in the idle state. Output load current

discharges the output capacitor, causing the output volt­age to decrease. As V

decreases, VC increases. As V

OUT

C

increases above VB, switching action begins, delivering
power to the output. The switch current sense threshold is
about 10mV in this VC region. If the output load remains
light, the output voltage will rise and VC will fall, causing
the converter to idle again. This is known as Burst Mode
operation. The burst frequency depends on input voltage,
output voltage, inductance and output capacitance. Out­put voltage ripple during Burst Mode operation is usually
higher than when the converter is switching continuously.
Burst Mode operation increases light load efficiency be­cause it delivers more energy per clock cycle than possible
with discontinuous mode operation and extremely low
peak switch current, allowing fewer switching cycles to
maintain a given output. IC supply current therefore be­comes a small fraction of the total input current.

Setting Output Voltage

The output voltage of the LT1619 is set with resistive
divider R1 and R2 connected from the output to ground as
detailed in Figure 3. The divider tap is tied to the device FB
pin. Current through R2 should be significantly higher
than the FB pin bias current of 25nA. With R2 = 10k, the
input bias current of the error amplifier is 0.02% of the
current in R2.

V

O

R1

= 1.24V 1 +

LT1619

FB

Figure 3. Feedback Resistive Divider

V

O

R1 = R2

R2

R1

()

R2

V

O

– 1

()

1.24

1619 F03

Synchronization and Shutdown

The S/S pin (Pin 1) can be used to synchronize the
oscillator to an external source. The S/S pin is tied to the
input (VIN > 1.9V) for normal operation. The oscillator in
the LT1619 can be externally synchronized by driving the
S/S pin with a pulse train with an amplitude of at least 1V.
The maximum allowable rise time is a function of the
pulse amplitude, as shown in Table 1. Rise times equal to

6

1619fa