5

HV7100

The HV7100 requires a single +16V to +75V supply to bias its

internal circuitry. It internally generates 3.3V for V

relative to V

an external V

5.5V), the internal regulator will shut off. The HV7100 drives

an external P-channel FET to drive the 24V/48V DC fan.

An external diode, connected across the fan terminals, is

required to clamp the voltage across the fan to a diode drop

during the off period.

Pulse Width Modulator

The PWM circuit compares the internal triangle wave

oscillator (0.5V – 2.5V pk-pk) with the linear control voltage

or the DAC output. Its output is a square-wave PWM signal

with duty cycle ranging from 0% to 100%.

When an external PWM signal is applied to the Enable input

and the internal PWM generator is not needed, R

should be connected to V

Oscillator

A capacitor connected between the C

frequency of the internal triangular frequency oscillator in

conjunction with the timing resistor R

discharge current into and out of C

The frequency is determined by the following equation:

P-Channel Gate Driver

The PWM output of the comparator circuit is level translated

and is the input to the gate drive circuit. The gate drive circuit

turns an external P-channel FET on and off by applying -12V

and 0V (reference to V

source. The -12V supply to the gate drive circuit is generated

internally from V

Enable

The EN pin directly controls the gate drive circuit. Pulling

this pin to logic ground applies 0V to the external P-channel

gate to turn it off. Applying a logic HIGH signal or pulling

the voltage to V

signal.

Speed Control

The fan speed can be controlled in three ways:

Linear Control - Applying a DC voltage between 0.5V to

2.5V to the LIN pin varies the duty cycle of the voltage driving

the fans from 0% to 100% according to:

Linear control voltage below 0.5V will turn off the fan

completely (0% duty cycle), while voltage greater than 2.5V

will fully turn the fan on (100% duty cycle).

When using linear control mode, DIN0 – DIN3 should be set

to logic 0. If desired, DIN may be used to set a lower limit on

the fan speed. This input is immune to moderate noise on

the control signal.

Digital Control - Applying logic signals to the DIN0 – DIN3

pins sets the duty cycle of the output. 0000 = 0% and 1111

= 100%. See Table 1 for details. In digital control mode, LIN

should be set to 0V. DIN0 – DIN3 pins have internal pull

downs so that the DAC output will default to 0V when it is

not used.

External PWM - An external PWM signal can be applied

to the Enable pin to directly control the duty cycle. A logic 0

turns the transistor off, and a logic 1 turns it on. When using

this control method, connect DIN0 – DIN3, LIN, and R

V

The DAC output and the Linear Control signals are OR’d

together. Whichever has the higher value dominates. This

allows an analog temperature sensing circuit to override the

digital inputs (DIN0 – DIN3) for added system protection.

The following table illustrates the correlation between the

digital inputs and LIN voltage to the PWM duty cycle.

Table 1. DAC signal and LIN voltage to

Duty Cycle Programming.

Functional Description

f

RC

TT

=

0 258

.

DIN3

DIN2

DIN1

DIN0

LIN

Gate Drive Duty Cycle

0000

0.500V

0%*

0001

0.633V

6.7%

0010

0.766V

13.3%

0011

0.900V

20.0%

0100

1.033V

26.7%

0101

1.167V

33.3%

0110

1.300V

40.0%

0111

1.433V

46.7%

1000

1.567V

53.3%

1001

1.700V

60.0%

1010

1.833V

66.7%

1011

1.967V

73.3%

1100

2.100V

80.0%

1101

2.233V

86.7%

1110

2.367V

93.3%

1111

2.500V

100%*

* Guaranteed 0% @ 0000 and 100% @ 1111

25

.

0

2

LI N

V

D