Abstract
Powerful graphic chips are prevalent in personal computers and gaming consoles. Power supply requirements for the graphic processors and supporting circuitry are extremely critical from a cost-performance point of view. In this article we present graphic card power supply solutions using MAX1953 1MHz pulse-width modulator (PWM) step-down controller.
Powerful graphic chips are prevalent in personal computers and gaming consoles. In games, presentations, and web surfing, 3D graphics now take center stage and a host of third-generation 3D-chips are arriving to deliver another quantum leap in 3D-performance and video quality over anything seen to date. Fill rates of greater than 500-600 Mpixel/s, triangle rates of 20 million/s, as well as the support of other enhancements will ask a lot more from game developers, CPUs, memory, RAMDACs and even display technologies. Additionally, the power supply requirements for graphic processors and the supporting circuitry have also increased dramatically.
Power supply requirements for the graphic processors and supporting circuitry are extremely critical from a cost-performance point of view. In this article we present graphic card power supply solutions.
- AGP terminations for input power:
- -3.3V @ 6A
=18.9W
- - 5.0V @ 2A =10.0W
- - 12.0V @ 1A =12.0W
- -3.3V @ 6A
- Typical Power Supply Requirements:
| Voltage | Current | Solution | |
| GPU (Graphic Processing Unit) | 1.2V or 1.5V | 5A | MAX1953 |
| DDR Memory (VDDQ) | 2.5V | 3A | MAX1953 |
- Typically inexpensive solutions are required with need for some generic failure features such controlled soft start, UVLO and current limiting.
- Single SO-8 package dual N channel MOSFET
- No current sense resistor
- Low input voltage operation (3.3V and 5V rails)
- 1 MHz switching for small size, low cost
- Efficiency >90%
Figure 1. The MAX1953: 1MHz switching, 1.5V/5A GPU supply, 3.3V In, 1.5V/5A out.
Table 2. Component List for 3.3V in, 1.5V/5A Output at MHz.
| Component ID | Quantity | Description |
| C1, 2, 3, 4 | 4 | Cap. 10µF/6.3V Cer 0805 Taiyo Yuden:JMK212F106ZG |
| C5 | 1 | Cap. 180µF/4V. Panasonic: EEFUE0G181R |
| C6 | 1 | Cap. 680pF/10V Cer 0402 Kemet: C0402C681M8RAC |
| C7 | 1 | Cap. 39pF/10V Cer 0402 Kemet: C0402C390K8GAC |
| D1 | 1 | Diode, Schottky, 40V, 1A, SOT-23F, Central: CMPSH1-4 |
| IC | 1 | IC, Synch. Buck controller: MAX1953 |
| L1 | 1 | Inductor, 0.68µH, 12A, 5mΩ. Coilcraft: DO3316P-681HC |
| R1 | 1 | Resistor, 7.15K, 1%, 0603 case |
| R2 | 1 | Resistor, 8.06K, 1%, 0603 case |
| R3 | 1 | Resistor, 82K, 5%, 0603 case |
| Q1/2 | 1 | Transistor, Dual MOSFET, Fairchild: FDS6898A, 20V, 0.013Ω |
Note: For 1.2V output, change R1 to 4.12K, 1%, and R3 to 68K, 5%.
Figure 2 shows the plot of efficiency versus output current of the 1.5V, 5A circuit.
Figure 2.
Figure 3. The MAX1953: 1MHz switching, 2.5V/3A memory VDDQ supply.
Table 3. Component List for 5V in, 2.5V/3A Output at 1MHz.
| Component ID | Quantity | Description |
| C1, 2, 3 | 3 | Cap. 10µF/6.3V Cer 0805 Taiyo Yuden:JMK212F106ZG |
| C4, 5 | 2 | Cap. 10µF/4V Cer 0805 Taiyo Yuden:AMK212BJ106MG |
| C6 | 1 | Cap. 560pF/10V Cer 0402 Kemet: C0402C561M8RAC |
| D1 | 1 | Diode, Schottky, 40V, 1A, SOT-23F, Central: CMPSH1-4 |
| IC | 1 | IC, Synch. Buck controller: MAX1953 |
| L1 | 1 | Inductor, 1.5µH, 3.4A, 30mΩ: Toko# 817FY-1R5M |
| R1 | 1 | Resistor, 17.4K, 1%, 0603 case |
| R2 | 1 | Resistor, 8.06K, 1%, 0603 case |
| R3 | 1 | Resistor, 33K, 5%, 0603 case |
| Q1/2 | 1 | Transistor, Dual MOSFET, Fairchild: FDS6898A, 20V, 0.013Ω |
Figure 4 shows the plot of efficiency vs. output current for the 2.5V, 3A circuit.
Figure 4.
The above circuits show that the MAX1953 can be used to generate both the GPU and the memory supply rails for graphic cards. The capability of operating down to 3V input of the MAX1953 allows the total output power to be drawn from both input supplies, 3.3V and 5V, so that neither of these rails is overloaded. The 1MHz switching frequency helps reduce filter inductor and capacitors size and cost.