MAX1385 Datasheet, PDF (47/52 Pages) Maxim Integrated Products – Dual RF LDMOS Bias Controllers with I2C/SPI Interface

Dual RF LDMOS Bias Controllers
with I²C/SPI Interface
Table 27. Basic Software Initialization
COMMAND
BYTE
0x64
0x64
0x20
0x22
0x24
0x26
0x28
0x2A
0x2C
0x2E
0x30
0x32
0x60
0x74
0x76
0x7A
0x7C
0x52
0x56
DATA
WORD
0x0008
0x0008
0x02A8
0x0EC0
0x02C1
0x0106
0x02A8
0x0EC0
0x02C1
0x0106
0x000F
0x0000
0x0000
0x00CC
0x0066
0x00CC
0x0066
0x01FF
0x01FF
DESCRIPTION
Bring the device out of shutdown mode.
Set internal reference and both DAC channels on.
Set the channel 1 high-temperature threshold to +85°C.
Set the channel 1 low-temperature threshold to -40°C.
Set the channel 1 high-current threshold to 4.3A for 50mΩ R_SENSE, Av_PGA = 2, and V_REFADC = 2.5V.
Set the channel 1 low-current threshold to 1.6A for 50mΩ R_SENSE, Av_PGA = 2, and V_REFADC = 2.5V.
Set the channel 2 high-temperature threshold to +85°C.
Set the channel 2 low-temperature threshold to -40°C.
Set the channel 2 high-current threshold to 4.3A for 50mΩ R_SENSE, Av_PGA = 2, and V_REFADC = 2.5V.
Set the channel 2 low-current threshold to 1.6A for 50mΩ R_SENSE, Av_PGA = 2, and V_REFADC = 2.5V.
Set Av_PGA1 and Av_PGA2 to 2, clock mode to 00 and ADC/DAC references to internal.
Set ALARM, SAFE1, and SAFE2 to depend on nothing (POR).
Set ALARM, SAFE1, and SAFE2 for push-pull/active-high (POR).
Set coarse DAC1 high wiper to 204.
Set coarse DAC1 low wiper to 102 (V_GATE = 1.99V for MAX1385, V_GATE = 3.98V for MAX1386).
Set coarse DAC2 high wiper to 204.
Set coarse DAC2 low wiper to 102 (V_GATE = 1.99V for MAX1385, V_GATE = 3.98V for MAX1386).
Set fine DAC1 to midscale.
Set fine DAC2 to midscale.
Table 26. Temperature-Threshold
Settings Examples
TEMPERATURE SETTING
-40°C
-1.625°C
0°C
+27.125°C
+105°C
TWO’S COMPLEMENT
1110 1100 0000
1111 1111 0011
0000 0000 0000
0000 1101 1001
0011 0100 1000
written to the Coarse DAC1/DAC2 Input Low Wiper reg-
ister. The resulting output when the low wiper is higher
than the high wiper is:
−
V_DACREF
2¹⁸
× FINECODE +
V_DACREF
2⁸
× LOWCODE
Basic Software Initialization
The MAX1385/MAX1386 do not power on all internal
blocks when full power is first applied. Software must
write to register 0x64 twice with bit D7 set to 0 during
initialization to enable full operation. A basic initializa-
tion sequence is shown in Table 27.
Regulating VGS vs. Temperature
The MAX1385/MAX1386 can be used along with a
microcontroller to perform closed-loop regulation of the
LDMOS FET bias current. For example, software can
read the temperature and use a calibrated look-up
table to determine a new value for the gate drive.
As an example, in noncontinuous conversion mode,
read temperature from remote diode 1 by writing to the
ADCCON register (0x62) with bit D1 set to 1. Wait for
BUSY to go high and then low. Read the ADC result
from the FIFO (0x80). The result bits D15–D12 = 0001
indicate the measurement source is the external tem-
perature sensor DXP1/DXN1, and bits D11–D3 indicate
two’s-complement temperature in degrees Celsius. Bits
D2, D1, and D0 are temperature subLSBs.
Gate voltage drive range must be previously deter-
mined during initialization by setting the coarse DAC1
high and low limits. Write a new value to FINETHRU1 to
immediately change the output GATE1 between the
high and low wiper limits based on the previous tem-
perature measurement.
The regulation software may also use the alarm thresh-
old limits to determine whether temperature and current
______________________________________________________________________________________ 47