6

+

–

Reference

V

1

V

2

0.1V swept 10Hz – 1MHz

0.1

µF

10.0V

4.00V

100K1%

100K1%

PSRR

Test Circuits

Detailed Description

Preregulator

The preregulator/startup circuit for the HV911X consists of a high-

voltage n-channel depletion-mode DMOS transistor driven by an

error amplifier to form a variable current path between the V

IN

terminal and the V

occurs when V

shuts off altogether when V

and 9.4V, so that if V

(generally the supply the chip is controlling). No current other than

leakage is drawn through the high voltage transistor. This mini-

mizes dissipation.

An external capacitor between V

to store energy used by the chip in the time between shutoff of the

take over powering the chip. This capacitor should have a value

of 100X or more the

effective gate capacitance of the MOSFET

being driven, i.e.,

C

as well as very good high frequency characteristics. Stacked

polyester or ceramic caps work well. Electrolytic capacitors are

generally not suitable.

A common resistor divider string is used to monitor V

the undervoltage lockout circuit and the shutoff circuit of the high

voltage FET. Setting the undervoltage sense point about 0.6V

lower on the string than the FET shutoff point guarantees that the

undervoltage lockout always releases before the FET shuts off.

Bias Circuit

is required by the HV911X to set currents in a series of current

mirrors used by the analog sections of the chip. Nominal external

bias current requirement is 15 to 20

µA, which can be set by a

390K

Ω to 510KΩ resistor if a 10V V

680K

Ω resistor if V

required;

± 5% is fine.

Clock Oscillator

The clock oscillator of the HV911X consists of a ring of CMOS

inverters, timing capacitors, a capacitor discharge FET, and, in

the 50% maximum duty cycle versions, a frequency dividing flip-

flop. A single external resistor between the OSC In and OSC Out

pins is required to set oscillator frequency (see graph). For the

50% maximum duty cycle versions the Discharge pin is internally

connected to GND. For the 99% duty cycle version, the discharge

pin can either be connected to V

through a resistor used to set a deadtime.

One difference exists between the Supertex HV911X and com-

petitive 911X’s: On the Supertex part the oscillator is shut off

when a shutoff command is received. This saves about 150

µA of

quiescent current, which aids in the construction of power sup-

plies to meet CCITT specification I-430, and in other situations

where an absolute minimum of quiescent power dissipation is

required.

Reference

The Reference of the HV911X consists of a stable bandgap

reference followed by a buffer amplifier which scales the voltage

up to approximately 4.0V. The scaling resistors of the reference

buffer amplifier are trimmed during manufacture so that the output

of the error amplifier when connected in a gain of –1 configuration

is as close to 4.000V as possible. This nulls out any input offset

of the error amplifier. As a consequence, even though the ob-

served reference voltage of a specific part may not be exactly

4.0V, the feedback voltage required for proper regulation will be.

A

≈50KΩ resistor is placed internally between the output of the

reference buffer amplifier and the circuitry it feeds (reference

output pin and non-inverting input to the error amplifier). This

allows overriding the internal reference with a low-impedance

voltage source

≤6.0V. Using an external reference reinstates the

input offset voltage of the error amplifier, and its effect of the exact

value of feedback voltage required.

Because the reference of the 911X is a high impedance node, and

usually there will be significant electrical noise near it, a bypass

capacitor between the reference pin and V

mended. The reference buffer amplifier is intentionally compen-

sated to be stable with a capacitive load of 0.01 to 0.1

µF.

+

–

Reference

V

1

V

2

60.4K

40.2K

1.0V swept 100Hz – 2.2MHz

Tektronix

P6021

(1 turn

secondary)

0.1

µF

+10V

(V

GND

(–V

(FB)

NOTE: Set Feedback Voltage so that

V

Error Amp Z

OUT

HV9110/HV9112/HV9113