Texas Instruments DRV2700EVM, Руководство пользователя

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REF
EXT INT
LIM
V
R K R
I
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Boost Converter
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14 SLOU403C – March 2015 – Revised June 2018
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DRV2700EVM High Voltage Piezo Driver Evaluation Kit
4.2 Disconnecting BST/PVDD
The DRV2700 has two essential blocks: the boost converter and the amplifier. If only using the
DRV2700’s boost converter, JP_VBST allows the user to disconnect PVDD from BST to shut down the
amplifier to save power.
WARNING
Be sure not to hot switch the BST and PVDD connection. This can
only be accomplished by removing or connecting the JP_VBST
jumper while the board is unpowered.
4.3 Programming the Boost Current Limit
The peak inductor current is set with resistor R3 (REXT). The current limit is not a safety mechanism, but
the highest value current the inductor will see each cycle. The inductor must be capable of handling this
programmed limit during normal operation. The relationship of REXT to ILIM is approximated with
Equation 2 where I
LIM
is the current limit set by R
EXT
, K = 10500, V
REF
= 1.35 V and R
INT
= 60 Ω .
(2)
4.4 Boost Inductor Selection
Inductor selection plays a critical role in the performance of the DRV2700. The range of recommended
inductor values is 3.3 µH to 22 µH. When a larger inductance is chosen, the DRV2700 boost converter
automatically runs at a lower switching frequency and incurs less switching losses; however, the larger
inductors may also have a higher equivalent series resistance (ESR), which will increase the parasitic
inductor losses. Smaller inductances generally have higher saturation currents; therefore, they are better
suited for maximizing the output current of the boost converter.
Table 5 lists several sample inductors that
provide adequate performance.
Table 5. Sample Inductors
Manufacturer Part Number DCR ( Ω ) Inductance (µH) I
SAT
(A) R
EXT
( Ω ) I
LIM
(A)
Coilcraft LPS4018-332MLB 0.080 3.3 1.9 7.32k 1.9
Coilcraft LPS4018-472MLB 0.125 4.7 1.8 7.5k 1.8
TDK VLS3012T-3R3M1R3 0.100 3.3 1.5 9.31k 1.5
4.5 Boost Capacitor Selection
The boost output voltage may be programmed as high as 105 V. A capacitor must have a voltage rating
equivalent to the boost output voltage or higher. A 250-V rated 100-nF capacitor of X5R or X7R type is
recommended for a boost converter voltage of 105 V. The selected capacitor should have a minimum
derated capacitance of 50 nF.
See Figure 13 for a diagram of the input configuration.