Datasheet

R =
EXT
K
V
REF
LIM
I
- R
INT
V = V
BOOST FB
1 +
R
R
1
2
FB
DRV8662
VBST
R1
R2
DRV8662
www.ti.com SLOS709A –JUNE 2011–REVISED NOVEMBER 2012
APPLICATION INFORMATION
PROGRAMMING THE BOOST VOLTAGE
The boost output voltage (VBST) is programmed via two external resistors as shown in the diagram below.
The boost output voltage is given by Equation 1
(1)
where V
FB
= 1.32 V.
VBST should be programmed to a value 5.0 V greater than the largest peak voltage expected in the system to
allow adequate amplifier headroom. Since the programming range for the boost voltage extends to 105 V, the
leakage current through the resistor divider can become significant. It is recommended that the sum of the
resistance of R1 and R2 be greater than 500 kΩ. Note that when resistor values greater than 1 MΩ are used,
PCB contamination may cause boost voltage inaccuracy. Exercise caution when soldering large resistances, and
clean the area when finished for best results.
PROGRAMING THE BOOST CURRENT LIMIT
The peak current drawn from the supply through the inductor is set solely by the R
EXT
resistor. Note that this
peak current limit is independent of the inductance value chosen, but the inductor should be capable of handling
this programmed limit. The relationship of R
EXT
to I
LIM
is approximated by Equation 2.
(2)
where K = 10500, V
REF
= 1.35 V, R
INT
= 60 Ω, and I
LIM
is the desired peak current limit through the inductor.
INDUCTOR SELECTION
Inductor selection plays a critical role in the performance of the DRV8662. The range of recommended
inductances is from 3.3 µH to 22 µH. In general, higher inductances within a given manufacturer’s inductor series
have lower saturation current limits, and vice-versa. When a larger inductance is chosen, the DRV8662 boost
converter will automatically run at a lower switching frequency and incur less switching losses; however, larger
values of inductance may have higher equivalent series resistance (ESR), which will increase the parasitic
inductor losses. Since lower values of inductance generally have higher saturation currents, they are a better
choice when attempting to maximize the output current of the boost converter. The following table has sample
inductors that provide adequate performance.
For inductor recommendations, see DRV8662EVM User's Guide (SLOU302)
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