Texas Instruments SN77203


The TI Programmable 88 calculator is powered by the BP88 battery pack containing one AA-size rechargeable NiCd cell. The electronics of the TI-88 is centered around the TP0485 Microcontroller family manufactured in a polysilicon gate CMOS process powered with 3 Volts while the drivers for the alphanumeric LC-Display with sixteen characters require an additional negative -4 Volts supply.

The SN77203 Display Interface Voltage Controller Chip integrates the following functional blocks:

1-cell to 3 Volts step-up DC/DC converter with internal reference voltage generation
1-cell to -4 Volts inverting DC/DC converter with digital On/Off control input
Low Battery Indicator with digital status output
Driver circuit for bidirectional serial calculator-to-calculator or calculator-to-peripheral communication

The SN77203 is highly integrated and requires only 4 external components for its application in the TI-88:

20 uH inductor for step-up DC/DC converter
300 uH inductor inverting DC/DC converter
1N4148 catch diode for inverting DC/DC converter
330 nF filter capacitor for internal voltage reference

Family Members and Applications

TI Programmable 88 Calculator, CA-800 Cassette Interface, PC-800 Printer

Technical Specifications

Item Min Typ Max Unit Comments
VBAT1   1.2   V  1-cell NiCd
VBAT2   1.2   V  1-cell NiCd
GND   0   V   
VCC   3.0   V  Always active
VDISP   -4.0   V  Activated with CONTROL Input 
LBI   0.9   V  Active 0.9 V, Hysteresis 0.2 V


The SN77203 was manufactured in a 8 um metal gate Bipolar process (metal width = 0.3 mil / 8.0 um, metal spacing = 0.3 mil / 8.0 um, diffusion width = 0.3 mil / 8.0 um, diffusion spacing = 0.5 mil / 13.0 um).

The die size of the SN77203 is approximately 120 mils * 65 mils / 3.0 mm * 1.7 mm.


The SN77203 uses a 0.3 wide 14-pin DIP (Dual In-line Package with a 0.1 / 2.54 mm lead pitch).

Pin Configuration

Pin IO Function Pin IO Function
1 V VBAT1 (1.5 V In) 14 I CONTROL (VDISP on/off)
2 V VBAT2 (1.5 V In) 13 V L2 (to GND)
3 V L1 (to VBAT1) 12 V VREF (C to GND)
4 V GND 11 O LBI (Low Battery Ind.)
5 V VCC (+3.0 V Out) 10 V VDISP (-4.0 V Out)
6 V VBUFF (+3.0 V Out) 9 I R (SI/O from TP0485)
7 IO SI/O (Peripheral Bus) 8 O K (SI/O to TP0485)

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If you have additions to the above datasheet please email:

Sean Riddle and oerg Woerner, January 22, 2021. No reprints without written permission.