SC1628

HIGH-EFFICIENCY STEP-UP DC-DC CONVERTER January 30, 1998 SC1628 TEL:805-498-2111 FAX:805-498-3804 WEB:http://www.semtech.com DESCRIPTION The SC1628 is a high performance step-up DC-DC converter, designed to drive an external power switch to generate programmable positive voltages. In the particularly suitable LCD contrast bias and flash memory programming power supply applications, typical full load efficiencies are 85% to 95%. The 4V to 24V input operation range allows the SC1628 to be powered directly by the battery pack in most batterypowered applications for greater efficiency. The output voltage can be scaled to 40V or greater by two external resistors. A pulse-frequency modulation scheme is employed to maintain high efficiency conversion under wide input voltage ranges. Quiescent current is about 100µA and can be reduced down to 8µA in shutdown mode. With a switching frequency range of 90kHz to 250kHz, small size switching components may be used, which is ideal for battery powered portable equipment such as notebook and palmtop computers. FEATURES • 4V to 24V input voltage operation • Adjustable output voltage • Low quiescent current at 100µA • Pulse-skipping and pulse-frequency modulation • • • maintain high efficiency (max. 95%) 90kHz to 250kHz oscillator frequency Power-saving shutdown mode (8µA typical) Push-pull driver output BLOCK DIAGRAM APPLICATIONS • Flash memory programming power supply • Positive LCD contrast bias for notebook and palm• • top computers Step-up DC-DC converter module Telecom power supply ORDERING INFORMATION DEVICE (1) PACKAGE SO-8 ABSOLUTE MAXIMUM RATINGS Parameter Supply Voltage SHDN Voltage Symbol VIN VSHDN TA TSTG Maximum 24 15 0 to 70 Units V V °C SC1628CS Note: (1) Add suffix ‘TR’ for tape and reel. PIN CONFIGURATION Operating Temperature Range Storage Temperature Range -65 to 125 °C © 1997 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320 HIGH-EFFICIENCY STEP-UP DC-DC CONVERTER January 30, 1998 SC1628 ELECTRICAL CHARACTERISTICS Unless otherwise specified, TA = 25°C, VIN = 13V Parameter Input Voltage Quiescent Current Shutdown Mode Current VREF Voltage VREF Source Current DLOW “ON Resistance” DHI “ON Resistance” CL Threshold Shutdown Threshold Shutdown Input Leakage Current VSHDN < 15V VIN - VCL 45 0.8 VFB = 1.5V VSHDN = 0V ISOURCE = 250µA 1.16 250 15 10 60 1.5 75 2.4 1 Conditions Min 4 100 8 1.22 Typ Max 24 200 20 1.28 Units V µA µA V µA Ω Ω mV V µA TYPICAL APPLICATIONS Color LCD Contrast Bias Supply , Flash Memory Programming Supply , © 1997 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320 HIGH-EFFICIENCY STEP-UP DC-DC CONVERTER January 30, 1998 SC1628 TYPICAL APPLICATIONS (cont.) 2-Cells to +12V Flash Memory Programmer , 4-Cells to +30V Low Power Supply Telecom +5V Supply © 1997 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320 HIGH-EFFICIENCY STEP-UP DC-DC CONVERTER January 30, 1998 SC1628 DEVICE OUTLINE - SO-8 PIN DESCRIPTIONS PIN 1: PIN 2: VIN VREF 4V to 24V input supply voltage. 1.22V reference output. Bypass with a 0.047µF capacitor to GND. Sourcing capability is guaranteed to be greater than 250µA. PIN 5: GND Power ground. PIN 6: DLOW Driver sinking output. Connected to the gate of the external N-channel MOSFET or the base of the NPN bipolar transistor. PIN 7: DHI Driver sourcing output. Connected to DLOW when using an external Nchannel MOSFET. When using an external NPN bipolar transistor, connect a base resistance RB from this pin to DLOW. RB value depends upon VIN, the inductor value and the NPN current gain. Current-limit input. The threshold voltage is 60mV from VIN. This pin clamps the switch peak current under abnormal conditions. PIN 3: SHDN Logical input to shutdown the chip: >1.5V = normal operation, GND = shutdown. Cannot be floating or forced greater than 15V. In shutdown mode DLOW and DHI pins are low. PIN 4: FB Feedback signal input to comparator. Connecting a resistance R1 to VOUT and a resistance R2 to GND yields the output voltage: PIN 8: CL VOUT = R1+ R 2 × VREF R2 (refer to typical application circuit). PIN CONFIGURATION © 1997 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320