HV300/HV310
Typical Application Circuit
GND
Long
Pin
Jumper
GND
Short
Pin
R1
487kΩ
R2
6.81kΩ
R3
9.76kΩ
8
V
DD
PWRGD
1
ENABLE
+5V
Cload
3
2
UV
OV
HV300LG or
HV310LG
DC/DC
PWM
CONVERTER
COM
RAMP
V
EE
SENSE
GATE
7
C1
10nF
Long
Pin
4
5
6
NOTES: 1. Undervoltage Lockout (UV) set to 35V
2. Overvoltage Lockout (OV) set to 65V
3. Remove Jumper if Short Pin is used
-48V
R4
50mΩ
Q1
IRF530
Application Information
Under Voltage and Over Voltage Detection
The UV and OV pins are connected to comparators with nominal
1.21V thresholds and 100mV of hysteresis (1.21V
±
50mV).
They are used to detect under voltage and over voltage
conditions at the input to the circuit. Whenever the OV pin rises
above its threshold or the UV pin falls below its threshold the
GATE voltage is immediately pulled low, the PWRGD signal is
deactivated and the external capacitor connected to the RAMP
pin is discharged.
The under voltage and over voltage trip points can be
programmed by means of the three resistor divider formed by
R1, R2 and R3. Since the input currents on the UV and OV pins
are negligible the resistor values may be calculated as follows:
UV
off
= V
UVH
= 1.16 =
|
V
EEUV
|
* (R2+R3) / (R1+R2+R3)
OV
off
= V
OVL
= 1.26 =
|
V
EEOV
|
* R3 / (R1+R2+R3)
Where
points.
V
IN
UV
off
= 1.16 = 35 * (R2 + R3) / 500K
R2 = (1.16 * 500K) / 35 – 9.76kΩ = 6.81kΩ.
The closest 1% value is 6.81kΩ.
Then R1 = 500K – (R2 +R3) = 483kΩ
The closest 1% value is 487kΩ.
Undervoltage/Overvoltage Operation
GND
UV
OFF
UV
ON
OV
ON
OV
OFF
|
V
EEUV
|
and
|
V
EEOV
|
are Under & Over Voltage Set
Pass
Transistor
ON
OFF
If we select a divider current of 100µA at a nominal operating
input voltage of 50 Volts then
(R1+R2+R3) = 50V / 100µA = 500kΩ
From the second equation for an Over voltage set point of 65
Volts the value of R3 may be calculated.
OV
off
= 1.26 = 65 * R3 / 500kΩ
R3 = (1.26 * 500K) / 65 = 9.69 kΩ
The closest 1% value is 9.76kΩ.
From the first equation for an Under Voltage set point of 35
Volts the value R2 can be calculated.
Current Limit
The current limit magnitude above which the current will not be
allowed to rise during startup is programmed using a sense
resistor connected from the SENSE pin to V
EE
pin. For example
to program a current limit of 1A, one would choose a resistor as
follows:
Rsense = 50mV / Isense
Rsense = 50mV / 1A
Rsense = 50mΩ
08/26/02rev.10b
©2002 Supertex Inc. All rights reserved. Unauthorized use or reproduction prohibited.
6
1235 Bordeaux Drive, Sunnyvale, CA 94089
TEL: (408) 744-0100 • FAX: (408) 222-4895
www.supertex.com
SUPERTEX [ Supertex, Inc ]
