All 32 sample and hold circuits share a common analog input, V SIG. The individual … over operating conditions, unless otherwise specified) High Voltage Amplifier.. 1235 Bordeaux Drive, Sunnyvale, CA 94089 ? Tel: 408-222-8888 ? www.supertex.com HV257 Features 32 independent high voltage amplifiers 300V operating voltage 295V output voltage 2.2V/µs typical output slew rate Adjustable output current source limit Adjustable output current sink limit Internal closed loop gain of 72V/V 12M? feedback …

General Description The Supertex HV257 is a 32-channel, high voltage, sample and hold amplifier array integrated circuit. It operates on a single high voltage supply, up to 300V, and two low voltage supplies, V DD and V NN . All 32 sample and hold circuits share a common analog input, V SIG . The individual sample and hold circuits are selected by a 5 to 32 logic decoder. The sampled voltage on the holding capacitor is buffered by a low voltage amplifier and amplified by a high voltage amplifier with a closed loop gain of 72V/V. The internal closed loop gain is set for an input voltage range of 0 to 4.096V. The input voltage can be up to 5.0V, but the output will saturate. The maximum output voltage swing is 5.0V below the V PP high voltage supply. The outputs can drive capacitive loads of up to 3000pF. The maximum output source and sink current can be adjusted by using two external resistors. An external R SOURCE resistor controls the maximum sourcing current, and an external R SINK resistor controls the maximum sinking current. The current limit is approximately 12.5V divided by the external resistor value. The setting is common for all 32 outputs. A low voltage silicon junction diode is made available to help monitor the die temperature….. Power Up/Down Issues External Diode Protection The device can be damaged due to improper power up / down sequence. To prevent damage, please follow the acceptable power up / down sequences, and add two external diodes as shown in the diagram on the right. The first diode is a high voltage diode across VPP and VDD, where the anode of the diode is connected to VDD and the cathode of the diode is connected to VPP. Any low current, high voltage diode, such as a 1N4004, will be adequate. The second diode is a Schottky diode across VNN and DGND, where the anode of the Schottky diode is connected to VNN, and the cathode is connected to DGND. Any low current Schottky diode such as a 1N5817 will be adequate. Acceptable Power Up Sequences The HV257 can be powered up with any of the following sequences listed below. 1) VPP 2) VNN 3) VDD 4) Inputs and Anode 1) VNN 2) VDD 3) VPP 4) Inputs and Anode 1) VDD & VNN 2) Inputs 3) VPP 4) Anode Acceptable Power Down Sequences The HV257 can be powered down with any of the following sequences listed below. 1) Inputs and Anode 2) VDD 3) VNN 4) VPP 1) Inputs and Anode 2) VPP 3) VDD 4) VNN 1) Anode 2) VPP 3) Inputs 4) VNN & VDD External Diode Protection Connection Suggested Power Up/Down Sequence The HV257 needs all power supplies to be fully up and all channels refreshed with V SIG = 0V to force all high voltage outputs to 0V. Before that time, the high voltage outputs may have temporary voltage excursions above or below GND level depending on selected power up sequence. To minimize the excursions: 1. The VDD and VNN power supplies should be applied at the same time (or within a few nanoseconds). 2. All channels should be continuously refreshed with V SIG = 0V, just before, and while the VPP is ramping up. Suggested VPP ramp up speed should be 10msec or longer and ramp down to be 1msec or longer….

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