VIN

SW

DRIVER

PWM

RT

CLK

VCC

HV-LDO

EN

FB

GND

5k

COMP

MAX DUTY

SHUTDOWN

STANDBY

UVLO

CLK

(Leading Edge Blanking)

RAMP

S

R

Q

VCC

ENABLE

ENABLE

Disable

VCC

ENABLE

CS

CS

RAMP

CS

SLOPE COMP RAMP

450 mV

0

+

Disable

ENABLE

CLK

×

CURRENT

LIMIT

1.5V

1.3V

+5V

1.26V

CURRENT

SENSE

50 m:

1.26V

+5V

+6.9V

2.8V

0.45V

6 PA

REFERENCE

GENERATOR

Av = 30

0.7

THERMAL

STANDBY

(165

OSCILLATOR

WITH

SYNC

CAPABILITY

1.26V

+

-

+

-

+

-

+

-

+

-

-

+

+

-

LM5001, LM5001-Q1

SNVS484H – JANUARY 2007 – REVISED JULY 2015

www.ti.com

7 Detailed Description

7.1 Overview

The LM5001 high voltage switching regulator features all the functions necessary to implement an efficient boost,

flyback, SEPIC or forward current mode power converter. The operation can be best understood by referring to

the block diagram. At the start of each cycle, the oscillator sets the driver logic and turns on the power MOSFET

to conduct current through the inductor or transformer. The peak current in the MOSFET is controlled by the

voltage at the COMP pin. The COMP voltage increases with larger loads and decrease with smaller loads. This

voltage is compared with the sum of a voltage proportional to the power MOSFET current and an internally

generated Slope Compensation ramp. Slope Compensation is used in current mode PWM architectures to

eliminate sub-harmonic current oscillation that occurs with static duty cycles greater than 50%. When the

summed signal exceeds the COMP voltage, the PWM comparator resets the driver logic, turning off the power

MOSFET. The driver logic is then set by the oscillator at the end of the switching cycle to initiate the next power

period.

The LM5001 has dedicated protection circuitry to protect the IC from abnormal operating conditions. Cycle-by-

cycle current limiting prevents the power MOSFET current from exceeding 1 A. This feature can also be used to

soft-start the regulator. Thermal Shutdown circuitry holds the driver logic in reset when the die temperature

reaches 165°C, and returns to normal operation when the die temperature drops by approximately 20°C. The EN

pin can be used as an input voltage undervoltage lockout (UVLO) during start-up to prevent operation with less

than the minimum desired input voltage.

7.2 Functional Block Diagram

8

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