Datasheet MAX5527, MAX5528, MAX5529 (Maxim) - 9

One-Time Programmable, Linear-Taper Digital Potentiometers MAX5527/MAX5528/MAX5529
U/D +11V PV 0V tCH tCL tCP tPH CS tPC 6 PULSES RECORD WIPER POSITION OPTIONAL 7TH LOCKOUT BIT Figure 5. One-Time Program Mode, Serial-Interface Timing Diagram
Table 1. One-Time Programming Options
TRACE PARASITICS
POWER-ON RESET ADJUSTABLE MODE WIPER POSITION WIPER
11V PV L Factory Default 22µF PARASITIC RPARASITIC Tap 31 Yes < 250µH < 40Ω (Unprogrammed) MAX5527 MAX5528 Programmed by Programmed position Yes MAX5529 Six CS Pulses Programmed by Programmed position No Seven CS Pulses Figure 6. PV Power-Supply Decoupling Change the wiper’s power-up position using the PV Pulse CS high for six cycles to change the wiper power- one-time programming sequence after power-up (see up position. The wiper position returns to this pro- Figure 5). After setting the wiper to the desired power- grammed position on power-up, but remains adjustable. up position, perform the following six-step sequence: Pulse CS high for seven cycles to lock the MAX5527/ 1) Set U/D and CS high. MAX5528/MAX5529 to a specific wiper position with no 2) Connect an external voltage source at PV in the further adjustments allowed. This effectively converts range of +11V to +11.55V. the potentiometer to a fixed resistor-divider. The sev- enth pulse locks the wiper position and disables the 3) Pull CS low. up/down interface. Once locked, connect U/D and CS 4a) Pulse CS high for six cycles, consisting of CS high, low, or leave them floating without increasing the starting low and going high for at least tCH, and supply current (see Table 1). then low for at least tCL, to change the wiper If six clock pulses are used, the interface is enabled power-up position. The wiper remains adjustable. and the device can be put into program mode again. 4b) Pulse CS high for seven cycles, consisting of CS However, the part uses one-time programmable (OTP) starting low and going high for at least tCH and then memory and should be programmed only once. If the low for at least tCL, to change the wiper power-up part is programmed more than once, all applied values position and lock the wiper in that same position. are ORed together. Thus, if 010101 is programmed the The seventh CS pulse is labeled the optional lock- first time and 101010 is programmed the second time, out bit in Figure 5. the result will be 111111. 5) Connect PV to GND or release the voltage source, The external PV power supply must source at least 5mA leaving PV floating. and have a good transient response. Decouple the PV 6) Pull CS high. power supply with a 22µF capacitor to GND. Ensure that no more than 250µH of inductance and/or 40Ω of para- sitic resistance exists between the capacitor and the device (see Figure 6).
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