LM2591HVT-5.0/NOPB National Semiconductor, LM2591HVT-5.0/NOPB Datasheet - Page 16

• Manufacturer Part Number: LM2591HVT-5.0/NOPB
• Description: IC REG SIMPLE SWITCHER TO220-5
• Manufacturer: National Semiconductor
• Series: SIMPLE SWITCHER®r
• Type: Step-Down (Buck)r

Specifications of LM2591HVT-5.0/NOPB

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 5V
• Current - Output: 1A
• Frequency - Switching: 150kHz
• Voltage - Input: 4.5 ~ 60 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Through Hole
• Package / Case: TO-220-5 (Bent and Staggered Leads)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -
• Other names: *LM2591HVT-5.0; *LM2591HVT-5.0/NOPB; LM2591HVT-5.0

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Application Information
This circuit has an ON/OFF threshold of approximately 13V.
lNVERTING REGULATOR
The circuit in Figure 11 converts a positive input voltage to a
negative output voltage with a common ground. The circuit
operates by bootstrapping the regulator’s ground pin to the
negative output voltage, then grounding the feedback pin,
the regulator senses the inverted output voltage and regu-
lates it.
This example uses the LM2591HV-5.0 to generate a −5V
output, but other output voltages are possible by selecting
other output voltage versions, including the adjustable ver-
sion. Since this regulator topology can produce an output
voltage that is either greater than or less than the input
voltage, the maximum output current greatly depends on
both the input and output voltage.
To determine how much load current is possible before the
internal device current limit is reached (and power limiting
occurs), the system must be evaluated as a buck-boost
configuration rather than as a buck. The peak switch current
in Amperes, for such a configuration is given as:
where L is in µH and f is in Hz. The maximum possible load
current I
While checking for this, take I
current limit value (min across tolerance and temperature is
1.2A for the LM2591HV). Also to account for inductor toler-
LOAD
is limited by the requirement that I
CLIM
FIGURE 9. Undervoltage Lockout for Inverting Regulator
to be the lowest possible
(Continued)
PEAK
≤ I
CLIM
.
16
ances, we should take the min value of Inductance for L in
the equation above (typically 20% less than the nominal
value). Further, the above equation disregards the drop
across the Switch and the diode. This is equivalent to as-
suming 100% efficiency, which is never so. Therefore expect
I
the above equation.
The reader is also referred to Application Note AN-1157 for
examples based on positive to negative configuration.
The maximum voltage appearing across the regulator is the
absolute sum of the input and output voltage, and this must
be limited to a maximum of 60V. For example, when convert-
ing +20V to −12V, the regulator would see 32V between the
input pin and ground pin. The LM2591HV has a maximum
input voltage spec of 60V.
Additional diodes are required in this regulator configuration.
Diode D1 is used to isolate input voltage ripple or noise from
coupling through the C
or no load conditions. Also, this diode isolation changes the
topology to closley resemble a buck configuration thus pro-
viding good closed loop stability. A Schottky diode is recom-
mended for low input voltages, (because of its lower voltage
drop) but for higher input voltages, a fast recovery diode
could be used.
Without diode D3, when the input voltage is first applied, the
charging current of C
eral volts for a short period of time. Adding D3 prevents the
output from going positive by more than a diode voltage.
PEAK
to be an additional 10-20% higher than calculated from
IN
IN
can pull the output positive by sev-
capacitor to the output, under light
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